To former US Ambassador to the UN Donald McHenry, Argentina's invasion of the Falkland Islands leaves the United States only one clear choice.
''The Argentine action sets a terrible precedent and must not be allowed,'' says Mr. McHenry. ''On the basis of principle, the US position is clearly on the side of the British.''
In an interview, McHenry says the administration's handling of the Falkland Islands dispute, pivoting on secretary of state unnecessary and unwise.
''We have ambassadors, telephones, telexes. . . . The secretary of state should be directing foreign policy, not engaged in the details of operation . . . making the whole thing into a flying circus,'' says McHenry, UN ambassador during the Carter administration.
Although troubled by Mr. Haig's role in the dispute, McHenry says the US should have a legitimate role as mediator.
He also suggests:
* That the Reagan administration's ''obsession'' with communism has led it to be overly tolerant of authoritarian regimes, including Argentina, which have ''trampled'' on human rights.
''This administration set out deliberately to improve our relations with Argentina - we stopped paying attention to the disappearance of hundreds of people and to the fascist nature of that government. . . . I believe Argentina may have concluded that it could get away with the Falkland Islands (takeover) with no opposition from the US.''
* That a careful reexamination of US Middle East policy is long overdue.
''We are seen by both adversaries and friends as totally one-sided. . . . My own feeling is that we've gone a great way to see that the legitimate aspirations of the Israelis have been realized. There will not be a resolution of the problems of the Mideast or of Israeli security unless we pay more attention to the legitimate aspirations of the Palestinians. . . . But if you dare to suggest that, you get cut off at the knees and can be the recipient of some of the most vicious mail and rumor. . . . I know from personal experience.''
* That the nuclear freeze movement, brought on in part by US slowing of arms negotiations talks and discussion of limited nuclear war in Europe, is sparking a ''healthy'' debate.
''I think we're going to hear a little less of this nonsense of surviving first and second strikes and having shelters, and we'll get a little more realism about what there is to survive. . . . I support the freeze idea. I think there are a sufficent number of weapons on both sides that we could cook each other any number of times over. . . .''
The former career diplomat, appointed to the UN post after Andrew Young resigned in 1979, is a professor at Georgetown University's School of Foreign Service and has started a consulting firm to advise US businesses about third world investment opportunities.
Mr. McHenry recalls that, despite predictions to the contrary, this country won UN support on such ''issues of principle'' as a demand that Iran release the hostages and a condemnation of the Soviet invasion of Afghanistan. But he says many of the disagreements with the US in the UN forum are the result of deep foreign policy differences among nations and must not be dismissed as simply anti-American or pro-Soviet.
''I don't think a US ambassador has to be passive, but I don't view the role as one of damage limitation,'' he says. ''I see it as more positive than that. The UN is an institution which the US ought to be trying to build. Institutions are built over a very long time with periods of ups and downs.''