The invasion of Grenada by US and Caribbean troops has triggered debate among experts on international law. But the legal question is not just a technical issue for experts. The legal basis for the invasion is questioned by several nations allied with the United States as well as by a number of congressmen.
If the weight of opinion on this issue shifts against the US, then it will obviously have an impact on America's image throughout the world. Some US experts argue that legal grounds for the invasion were flimsy, and that the US has now lost the propaganda advantage it held over the Soviet Union because of the Soviet invasion of Afghanistan. Others argue that the US can make a case for the invasion based on certain provisions in the United Nations Charter and a 1981 treaty establishing the Organization of Eastern Caribbean States (OECS).
So far, the reaction from nations outside the Caribbean region has been far from encouraging to the US. Britain expressed doubts about the invasion plan. France called the invasion ''surprising'' in relation to international law. The Soviet Union, through the official Tass news agency, accused the US of seeking to intimidate ''freedom loving'' people in Latin America through a ''criminal'' action.
The White House announced that a US military aircraft carrying 61 people left Grenada Wednesday in the first evacuation of American citizens from the island. A spokesman said that other flights would follow. There are some 1,000 Americans on the island, more than half of them medical students.
In justifying the invasion, Secretary of State George P. Shultz noted on Tuesday that the OECS treaty provides for collective security. Mr. Shultz said that President Reagan decided to respond to an OECS request to intervene in Grenada, in order to protect American citizens on the island and help OECS states establish order and popularly supported governmental institutions.
Some congressmen, as well as some Europeans and Latin Americans, note the OECS is a little-known organization, whereas the better known Organization of American States (OAS) has a charter that provides that no state has the right to intervene in the affairs of another state. The US belongs to the OAS, but it does not belong to the OECS. Officials at the OAS from key Latin American nations have criticized the action in Grenada.
Rep. Michael Barnes (D) of Maryland, who chairs the House subcommittee on Western Hemisphere Affairs, has argued that the invasion raises ''some serious international legal questions.''
Congressional critics like Representative Barnes note that the article in the OECS treaty that Mr. Shultz cites calls for collective security against ''external aggression'' and further states that decisions by member states ''shall be unanimous.'' Although several of the eastern Caribbean countries apparently felt threatened by Grenada, it is not clear that any external aggression against them was under way. And since Grenada, a member of the OECS, did not agree to the action taken, the action was not based on unanimity.
Prof. Louis Sohn at the University of Georgia said that based on existing treaties, a good legal case could be made both for and against the American intervention. Professor Sohn said that in the end, much might depend on whether the US can help restore order in Grenada and bring about elections, preferably under international supervision.
Leo Gross at Tufts University's Fletcher School of Law and Diplomacy said that traditionally a government has the right to protect its citizens, but that a question arises as to whether American citizens on Grenada were threatened with violence. He said that it was not at all certain the violence in Grenada that preceded the invasion resembled anything like the violence that prevailed in the Dominican Republic when the US intervened in that island nation in 1965.
Article 51 of the UN Charter permits acts of self-defense, but Professor Gross said that in the case of the invasion of Grenada, ''It would require more imagination than I have to invoke Article 51.''
But John Moore at the University of Virginia, a former counselor on international law to the Department of State and ambassador to the Law of the Sea negotiations under the Ford administration, contends that a strong case can be made for the Grenada intervention under the UN Charter.
Professor Moore cites the the combined effect of the Charter's Chapter VIII, which permits regional arrangements to deal with international security, and Article 51, dealing with the right to self-defense. He said that Grenada's military buildup, a threat from Grenada perceived by nations in the region, and a serious breakdown of law and order on the island that might have led to the taking of American citizens as hostages, helped justify the invasion.
Moore added that the presence of Cuban troops and Soviet advisers on the island had effectively removed the small nation's ability to exercise self-determination, a fundamental underlying principle of both the UN and OAS Charters.