INTERNATIONAL LAW. As the US shifts position on key legal issues, critics say the administration is eroding support for international law. Others argue change is needed in a time of global turmoil.

International law seems to have fallen on hard times. Few would claim that the United States can always make international law its overriding concern in the conduct of foreign policy. The system of law is imperfect and the tools of enforcement limited.

But there is concern among many legal and diplomatic experts that the Reagan administration has retreated from the traditionally strong emphasis placed on international law throughout US history.

The erosion is seen in a number of developments over the past five years. Under the Reagan administration the US has:

Ended its adherence to the general compulsory jurisdiction of the World Court.

Refused to sign the 1982 Law of the Sea treaty negotiated on a bipartisan basis and signed by 156 nations, or to join with others to revise the six out of 400 articles to which it objects.

Reinterpreted the 1972 Antiballistic Missile (ABM) treaty to make possible development of the President's antimissile defense plan known as ``star wars.''

Departed from the position of previous administrations that Israeli settlements in the West Bank are illegal.

Held back from ratifying two 1977 protocols to the 1949 Geneva Conventions on combatants and war victims. A new unilateralism

These and other actions come against the background of a general move away from the internationalism of the post-World War II decades toward a more unilateralist approach in world affairs and a skeptical view of global institutions.

The United States has withdrawn from UNESCO, for example, on grounds the organization has become overpoliticized. It has stood alone in the World Health Organization against efforts to improve the use of instant milk formula. It has gone back on its pledge to increase funding for the International Development Association, an affiliate of the World Bank, and threatened to withdraw from the United Nations Conference on Trade and Development and some other UN bodies. It is also seeking to reduce its financial contribution to the UN budget.

``This administration has adopted a policy of unilateralism greater than that of any previous administration,'' says David Newsom, director of Georgetown University's Institute for the Study of Diplomacy. ``If we can claim some action is in our interest, we do it -- regardless of international law.''

The Independent Commission on Respect for International Law, a recently formed group of legal specialists, describes the Reagan years as ``a period during which the United States has moved decisively from being a champion of law and internationalism to being an abettor of old-fashioned unilateralism that refuses to be tied down by legal restraints, that treats laws like fences, made to be climbed.''

The one acknowledged exception to the trend is the administration's approach to international trade and economics. President Reagan, strongly resisting protectionist sentiments in Congress, is committed to open and fairer trade practices and to strengthening procedures for settling trade disputes.

Conservative scholars dispute the contention that US regard for international law has diminished. The President is pursuing more ``realistic'' policies, they say, which in the end will strengthen international law and improve world institutions.

Even critics of the administration hold differing opinions on a number of issues.

Many experts acknowledge, for instance, that provisions of the Law of the Sea treaty governing deep-sea mining are flawed and should be reworked. And some committed supporters of the UN did not object to the US walking out of UNESCO, which they feel has violated its own charter. Molding the law to fit policy?

Many international lawyers, however, are troubled by what they see as a fundamental shift in the US attitude and approach. They note that there is a difference between choosing not to pursue international law in a given foreign policy decision and eroding the law by molding it to fit the policy.

``There are times when I think that the [State Department] legal adviser has been put in the position of a client who says to the lawyer: `This is what I'm going to do, and you do your best with the law of the matter,' '' says former US Secretary of State Dean Rusk.

Recently, Abraham D. Sofaer, legal adviser to the State Department, startled the diplomatic community when he suggested in an interview in an Israeli newspaper that Israel's invasion of Lebanon in 1982, which led ultimately to the collapse of the Lebanese government, was justified on grounds of self-defense. At the time it was widely perceived that Israel had violated international law. But the Sofaer comment accords with the administration's increasingly close ties with the state of Israel.

In an effort to combat terrorism, the State Department has also interpreted international law to permit such actions as the seizure of the Egyptian airliner carrying the hijackers of the Achille Lauro cruise ship.

``A nation attacked by terrorists is permitted to use force to prevent or preempt future attacks, to seize terrorists, or to rescue its citizens when no other means is available,'' US Secretary of State George P. Shultz told a Pentagon-sponsored conference in January.

Mr. Shultz was in part responding to British Prime Minister Margaret Thatcher's view that the use of retaliatory or preemptive strikes violated international law and that terrorism should be fought by legal means. What disturbed some observers of the airline seizure in particular was the go-it-alone air conveyed in the President's remark, ``We did this all by our little selves.'' Trying to regain US supremacy

This trend toward unilateralism is seen to stem from two factors: President Reagan's effort to regain US supremacy in the world and a current American mood of disenchantment with internationalism.

``The nation is past the high point of its power,'' comments Hermann Eilts, a former US diplomat teaching at Boston University. ``It may be the strongest militarily, but it has to share power and we're becoming increasingly defensive attitudinally and psychologically.''

Further, the American climate has changed. The old internationalist spirit appears to be giving way to a resurgent nationalism.

Foreign policy experts suggest that US failures in Vietnam, the Middle East, and Central America, along with the impact of world events on the domestic economy, have affected the idealism of past decades. Americans have become irritated with world institutions and frustrated over the loss of US preeminence abroad. Television, too, is having an impact.

``The unremitting impressions of violence, famine, terrorism, irrationality, and conflict engender deep new feelings of hostility and cultural irreconcilability,'' writes Thomas L. Hughes, president of the Carnegie Endowment for International Peace, in Foreign Policy magazine. ``Iran's Ayatollah Ruhollah Khomeini has chilled the warmth of the global village.''

The US decision not to follow a policy of automatic compliance with decisions of the World Court is viewed as a particularly sharp blow to efforts to strengthen international law.

The decision was made when the court decided it had jurisdiction to hear Nicaragua's suit against the US for participating in the mining of Nicaraguan harbors and supporting Nicaragua's rebel insurgency.

The US, deeming this essentially a political dispute that did not belong in the International Court of Justice, as the World Court is formally known, chose to retire from the compulsory jurisdiction of the court rather than argue its case.

``This placed us in a thoroughly indefensible position,'' says Clark Clifford, a practicing lawyer who has held a number of high posts in Democratic administrations. ``We had been one of the outstanding supporters of the World Court, and we decided we would not take our medicine but would get out.''

A legal adviser in a past Republican administration observes: ``The administration has thrown away 100 years of moving toward compulsory jurisdiction, slim as it is,'' he comments. ``Now it may take another 100 years to get anything resembling compulsory jurisdiction.''

The recent American naval operations against Libya also have drawn fire among some in the legal community. The US has a perfect right to sail into the Gulf of Sidra, which is considered international waters. But the deliberate provocation of Libyan leader Muammar Qaddafi is viewed as a questionable departure from international custom.

Says Mr. Clifford: ``It is unwise, dangerous, and irresponsible to go test that boundary when it does not mean anything practically to us. You don't ordinarily choose to provoke disputes about boundary lines that are in dispute. . . . It is the wrong policy to go about engaging in provocative acts -- whether mining Nicaraguan waters, sailing into Soviet waters, or steaming into Sidra.'' Controversy over the use of force

Undoubtedly the most controversial issue is that of the use of force in relations among states, an area where the US and the Soviet Union are criticized for contributing to a decline in restraint in the use of force.

``There has been a sharp reversal of what has been a 40-year-old commitment to trying to promote the rule of law with regard to use of force,'' says Burns H. Weston of the University of Iowa.

Nicaragua is cited by legal experts as a conspicuous example. Even such a bedrock conservative as US Sen. Barry Goldwater (R) of Arizona fired off a stern letter to CIA Director William Casey deploring the US role in the mining of Nicaragua's harbors as being a violation of international law.

US aid for the rebel ``contras'' is also viewed by many as a violation of the charters of the UN and the Organization of American States, which establish the principle of national sovereignty and noninterference in the affairs of another state. The US maintains diplomatic relations with Nicaragua, and, therefore, funding an insurgency against a recognized government raises legal issues, i.e., infringement of the laws of neutrality and belligerency.

But the issues become blurred when a government is known to be trying to subvert another government -- not by direct armed attack but by clandestine means, as the Sandinistas have been doing in El Salvador and other countries.

``When there is a shift from open invasion to covert attack -- through terrorism, conspiracy, and so on -- there is a tendency for the attack to become politically invisible,'' says John Norton Moore of the University of Virginia. ``The temptation is to have a fuzzy notion that we should not use force in response to such an attack.''

``If there is no difference between a covert armed attack and a covert defensive response, there is no difference between aggression and defense and you have in effect destroyed the UN Charter,'' says Professor Moore, who is chairman of the American Bar Association's Standing Committee on Law and National Security. The Reagan administration, he maintains, is in effect strengthening the international system.

To this, many international lawyers respond that the administration has not presented a convincing case of a ``covert armed attack'' by Nicaragua on its neighbors. `It's not 1946'

Administration supporters further argue that previous administrations were trying to live a ``myth'' that has died. The world has gotten rougher, the argument goes, and legal standards are being violated everywhere.

``It's not 1946, when everyone thought the UN would save the world,'' says a former legal adviser in the Reagan administration. ``So what does the US do -- continue to hope and pray that standards will be followed, when they're not, or are there areas that require re-analysis?''

Others see the situation differently. Today US foreign policy is largely shaped by President Reagan's strong anticommunism and his tendency to view international issues in the context of East-West relations. This, diplomatic experts say, affects adherence to international legal norms, making it possible to invoke the principle of ``self-defense'' for actions that are legally questionable.

The administration appears to want as few restraints on its actions as possible. And so it uses international law selectively and conveniently to help carry out policy objectives -- as when it sailed into the Gulf of Sidra.

What troubles many legal and diplomatic experts is the administration's reluctance to use the instruments of collective action, however weak, to try to resolve the Nicaraguan problem. Previous administrations, for instance, turned to the OAS Charter or the Rio Treaty to generate a regional response to aggression, and most significantly an aggression that is not an armed attack.

``The US should be putting the Nicaraguan issue before the OAS with insistence and conviction,'' says Mr. Rusk. ``If the OAS Council were meeting regularly, more facts would come to light about Nicaragua's activities and the US hand might be strengthened.''

``It's a problem for the whole hemisphere, and we're letting it become a unilateral issue,'' says Rusk, a professor at the Georgia University School of Law.

Elliot Richardson, US attorney general in the Nixon administration and a negotiator of the Law of the Sea treaty, echoes this view.

``The United States should first create a regional framework within which countries of the region commit themselves to refrain from subversive acts and reject any foreign military presence,'' he says. ``Then if we acted to control the risk [of a Soviet and Cuban presence] we would be in the position of invoking sanctions and acting on the foundation of law.''

When the US resorts to use of force without first laying the legal basis for it, says Mr. Richardson, the perception of American power is weakened. Thus, the public sees that the US will not invade Nicaragua but will use force to squash Grenada.

``So you have weakened long-term influence by creating an illusion of power,'' Richardson says. ``I would not argue that we should never use force -- policy is hampered if you remove it. But I would pick the places and lay the foundation for its legitimacy.''

Still other specialists point to the possible adverse political consequences of disregarding regional treaties. ``Nicaragua will identify us with right-wing suppression and the Nicaraguan communists with reform,'' says Alfred Rubin, a scholar at the Fletcher School of Law and Diplomacy. ``I do not see where the US gets on the side of determining what governments people want. When we say revolution is illegal, we depart from the Declaration of Independence.''

However imperfect the present system of international law, fostering that system is deemed crucial in today's interdependent world. International law contributes to global stability and peaceful intercourse among nations. It is, in Mr. Clifford's words, the ``lubricant'' that keeps the international community operating smoothly.

The US took the lead in fostering a world order based on the observance of rules and the establishment of world institutions to help uphold them. If the US comes to be be perceived as sometimes indifferent to the rules, concerned observers say, this will undercut its efforts to hold other nations to legal and moral standards.

``From the point of view of the middle and little countries, the current US retreat from internationalism is a bad thing,'' comments a prominent third-world ambassador to the US. ``Our interests are jeopardized when there is a decline in the rule of law and if the greatest power in the world retreats from the system.''

Instead of seeming to go it alone, say experts, the US should seek to build a stronger framework of international law and institutions, look for opportunities to use them, and thereby strengthen them.

In Richardson's words, ``The better respected these institutions are, the better served long-term US interests will be.''