Impact of Reagan Cabinet switch

Strong direction of foreign policy can be expected from President Reagan for the remainder of his first term in office, administration officials say. The officials say that this is one of the main legacies left by the outgoing national security adviser to the President, William P. Clark: to get Reagan more deeply involved in foreign affairs.

A series of crises around the world, from Central America all the way to the Philippines, would seem to demand ever greater presidential involvement. So would election-year politics. Polls show that a mishandling of foreign affairs could damage the President's reelection chances should he choose to run again, a prospect which now seems assured.

At the same time, the departure of Judge Clark from the top national security post at the White House would appear to strengthen, at least temporarily, the hand of Secretary of State George P. Shultz. Clark had assumed a leading role in the fields of arms control and Central America and some aspects of Middle East policy. Clark's successor will have to go through a period of settling in, during which time the State Department will be expected to provide continuity on a number of issues.

Experts outside the government are predicting, meanwhile, that Clark's departure will also reinforce a trend toward pragmatism in Reagan's foreign policy, a trend which has not always been evident in the President's rhetoric. A recent example of the pragmatic trend was Reagan's handling of the Soviets' shooting down of Korean Airlines Flight 7 on Sept. 1. Reagan spoke harshly of the Soviet Union following the incident, but his actions were measured. The sanctions announced - closing Soviet airline offices in the United States and setting further limits on cultural and other exchanges, for example - were limited.

Pragmatism has also been reflected in the President's approval of a huge new grain agreement with the Soviet Union and in his determination to keep arms reduction talks going with the Soviets. Reagan has overruled subordinates who proposed denying the Soviets new American oil- and gas-drilling equipment. The President has made compromises with moderate Democrats and Republicans in the Congress over arms control proposals. Earlier this month, Reagan overrode objections from the Defense Department and embraced the ''build down'' concept for nuclear arms reductions suggested by two key Senators. He also injected new flexibility into his initially tough proposals for strategic arms reductions.

At this writing, the leading candidate for the post of national security adviser is reported to be Robert C. McFarlane, who is currently serving as deputy assistant to the president for national security and as special envoy to the Middle East. Mr. McFarlane is a low-key professional with long experience in the White House. The former Marine colonel is so self-effacing that until he was appointed to his roving Middle East job a few months ago, few photographs were publicly available.

McFarlane is regarded by many of the Congressmen who have dealt with him as moderate, pragmatic, nonideological and well-informed. A similar view prevails at the State Department. Officials there, who have engaged in many a battle with national security advisers, including Judge Clark, say that they would be happy with the choice of McFarlane for the job.

But objections to McFarlane's selection as national security adviser have come from a number of conservative supporters of President Reagan outside the administration who would like to see United Nations Ambassador Jeane J. Kirkpatrick get the job. Inside the administration, opposition is reported to have come from Defense Secretary Caspar W. Weinberger and CIA Director William J. Casey, who are said to fear that McFarlane will not be forceful enough in presenting their views to the President. A close friend of Reagan's, Clark had easy access to the President. He also shared some of the hardline views for which Weinberger and Casey are noted.

The president's national security adviser is supposed to be an honest broker, presenting the president with all of the foreign policy options proposed by the State Department, Defense Department, and other government agencies. He is then supposed to see to it that the president's decision is implemented.

If the national security adviser is a strong personality, as were Henry A. Kissinger, Zbigniew Brzezinski, or, for that matter, Judge Clark, it almost inevitably seems to bring him into conflict with State Department professionals who view themselves as the top experts on foreign policy. If the national security adviser is less forceful, it sometimes permits bureaucratic warfare between the State and Defense departments to get out of control.

One well-informed administration official predicted, however, that no matter who is appointed to replace Clark, he or she will inevitably meet resistance at the State Department. The department's traditional attitude, the official said, is that ''foreign policy is our business. Don't bother us.''

During William P. Clark's tenure at the White House, State Department officials complained as much as anything else about the tendency toward ideological rhetoric which President Reagan has engaged in. On matters of substance, in contrast with Clark, Secretary of State Shultz doubted the efficacy of proposed trade sanctions against the Soviet Union. Shultz also seemed to be more skeptical about the usefulness of increased American military involvement in Central America than Clark was.

But many of the complaints against Clark from State Department officials related more to style than substance. Officials said Clark, apparently because of his inexperience, sometimes had difficulty recommending the proper mix of military and diplomatic moves by the President.

A series of foreign crises now dictates that President Reagan choose a national security adviser who is more experienced than Clark was when he took the job:

* In the shooting wars in Lebanon and Central America, the administration is playing an active and highly visible diplomatic and military support role.

* In the Philippines and South Korea, where tensions now run high, the administration is using quiet diplomacy to urge restraint on authoritarian leaders, never an easy exercise for any administration.

* At the same time, deteriorating US-Soviet relations demand renewed attention. The Soviets are threatening to walk out of the arms control talks in Geneva.

* And added to all this is the Iran-Iraq war, which again seems to threaten the oil-producing nations friendly to the US. US concern over this latter arena has been dramatized by the revelation that the US has had plans to equip a Jordanian intervention force for the Gulf. This controversial plan is opposed by Israel.