A year-and-a-half ago, when Norman Mailer assumed the presidency of PEN American Center -- the American branch of an international network of poets, novelists, playwrights, essayists and translators -- there were some misgivings in the ranks. The fear was that Mailer would make this just another advertisement for himself, appearing grandly only on ceremonial occasions.

In admirable fact, Mailer has worked hard and long at the affairs of PEN, proving particularly effective at the fund-raising and orchestrating necessary to bring off the largest gathering of writers ever to appear in this country -- the 48th International PEN Congress, which opened in New York last Sunday. More than 600 literary figures from 40 countries were in attendance.

At one point during the preparations, however, Mailer could not resist slipping back into his familiar stance as emperor of the literati. Without consulting the board of American PEN, he invited a plenipotentiary of his own rank, Secretary of State George Shultz, to join him at the opening session. Sensing a certain disquiet among board members, Mailer apologized for his act of unilateral diplomacy, but the invitation was allowed to stand. "By that point," a board member told me, "we felt we had to support Norman's mistake."

Actually, Mailer disagrees vehemently that he made a mistake, despite the bitter reaction to the invitation among many PEN members from this and other nations. Among the dissidents were E. L. Doctorow, three past presidents of the American PEN Center and Nadine Gordimer, a vice president of International PEN. Gordimer refused to attend the opening session, somehow having lost confidence in the secretary of state as a force for free expression in South Africa. Also, there were 65natures of PEN members on a letter protesting Shultz's presence. During Shultz's speech, several writers walked out and others mockingly counterpointed some of his comments.

Norman Mailer apologized to the secretary of state for this and other displays of "silly bad manners." Mailer, moreover, refused to read aloud the letter of protest. To do so, the aesthete explained later, would have spoiled the "form" of the meeting. Besides, Mailer insisted that Shultz's coming meant "the United States government, no matter how far right, was willing to accept the importance of writers."

And Shultz did acknowledge that importance in a speech composed of burnished boilerplate on the symbiotic relationship between writers and freedom. Shultz ended: "Don't be so surprised by the fact that Ronald Reagan and I are on your side."

Surprise wasn't the word. Disbelief comes closer. After all, one of the better known cases brought on behalf of foreign writers and political figures excluded from this country under the McCarran-Walter Act is Allende v. Shultz. (Hortensia Allende is the widow of the assassinated president of Chile, Salvador Allende.)

At the PEN gathering, Shultz claimed that McCarran-Walter is being administered more sensitively these days, but as Sen. Charles Mathias pointed out in The Post (op-ed, Jan. 12), the provisions of this act that bar people because of their ideas cannot be just fixed up. They have to be abolished. A public word to that effect from the secretary of state would help a great deal. He did not give it at PEN.

In December, Shultz had been in Romania, where he urged more trade between that country and ours. Amnesty International's 1985 report tells of a man sentenced to six years in prison there because he'd written a letter to Romanian radio and television asking for more programs in Hungarian.

And it was George Shultz who, reacting to American press criticism on the invasion of Grenada, snarled: "It seems as though the reporters are always against us . . . always seeking to report something that's going to screw these things up."

Well, as Shultz told PEN, "Freedom is real, and it works."

As for Ronald Reagan's being a fan of free expression, it has been under his administration that the FBI's guidelines on undercover operations have been elasticized to permit full field investigations on the basis of what someone merely advocates, and it was under this president that, for the first time in our history, covert government agents slipped into churches and recorded the services and prayer meetings of sanctuary workers.

Actually, Norman Mailer might better have invited a man who exemplifies the way our system of free expression works in spite of Shultz and Reagan. I mean First Amendment lawyer Floyd Abrams, who has fought many battles against the Reagan administration, and has won some.

Or perhaps Abrams could hav been asked to respond to Shultz's speech -- crumbling the newspeak before the writers of the world.