Georgi A. Arbatov is the head of Moscow's Institute of U.S. and Canadian Studies. He is considered by most students of the subject to be the Soviet Union's best authority on the United States, and an influential figure in the Kremlin. So when Arbatov talks, people listen--American officials, academics, news commentators.

They listen not so much because they believe what he has to say, but because what he has to say is generally taken to be what the Soviets would have us believe is their official line at any given time. Thus he serves as a sort of rough barometer, well worth checking for significant changes in attitude or atmosphere.

There was, therefore, a large turnout of distinguished figures from the State Department, congressional committee staffs, academia, leading local think tanks, television and the writing press when Arbatov did his familiar number at a dinner discussion hosted by the Carnegie Endowment for International Peace the other night.

But there was one oddity, wryly taken note of by Arbatov: the presence of the "media" came close to contravening a restriction imposed on him, apparently for the first time, by State Department order.

Arbatov's latest American tour is at the invitation of Grinnell College in Iowa and the Dartmouth Conference, a private symposium on U.S.-Soviet affairs. He has lectured to public gatherings of over 1,000 people, and spoken openly at a series of breakfasts and luncheon meetings. Although he cancelled one news conference, he did give interviews to the Des Moines Register and Iowa public television.

But even these strictly "local" media contacts, according to State Department press officer Anita Stockman, were "contrary to the purposes for which his visa had been issued."

How petty and pointless can you get? More precisely, to what lengths--or depths--is the Reagan administration prepared to go to preserve the purity of American public discourse in its crusade against the "evil" of international communism? One would have thought that a nadir had been reached with the denial of an entry visa to the 68-year-old widow of Chilean president Salvador Allende, on the grounds of her membership in the World Peace Council, which, the State Department said, "has a direct political affiliation with the Communist Party of the Soviet Union."

For her to come to the United States on the invitation of the Roman Catholic archdiocese in San Francisco, Stanford University and the Northern California Ecumenical Council, it was judged, would have been "prejudicial to the public interest" in a way that could "endanger the welfare, safety or security of the United States" under the terms of the Immigration and Nationality Act.

As silly as that may sound--if you assume a sturdy resilience on the part of the American public and a measure of confidence in American values and institutions--the Arbatov case strikes me as even sillier. For one thing, thanks to the marvels of modern communications, he can be (and has been) bounced off a satellite from Moscow to American TV screens, for which he needs no visa. For another, his public lectures and private discussions on his recent tour gave him ample opportunity to press the new Soviet line.

So what, exactly, is the rationale for the minor inconvenience, loosely enforced, of a State Department edict against "any contact with the media"? It is an issue of principle, officials insist. The recently enacted Foreign Missions Act is designed to promote "reciprocity" in the treatment of American diplomats on matters having to do with travel restrictions, the location or protection of embassies, communications, immunity. This administration believes its terms should apply, as well, to access to the media. Our ambassador's pronouncements go unreported in the Soviet Union. So, tit-for-tat, we'll muzzle Arbatov.

Now, reciprocity has its uses in some instances having to do not only with our missions abroad but with treatment of U.S. citizens or news representatives-- when there is real leverage on our side. The Soviets care, for example, if we throw out their Izvestia correspondent in retaliation for the expulsion of an American correspondent. It sometimes works if we restrict the movements of their diplomats in reprisal for travel restraints they impose.

But the United States cannot block Soviet access to an American free press. So there is no way to apply leverage, and still less point in trying. For what we are demanding is that the Soviets have a free press--which is to say, an open society. And that, in turn, is to say that the Soviets should stop being communists.