AFTER TWO MONTHS of being for the most part remarkably accommodating while trying to manipulate the world's news media, the Iranian government -- or what passes for it -- has now embarked on a different course. It is threatening to expel reporters -- particularly Americans, Britons and West Germans -- who do not write or speak the "truth." That "truth," of course, is the version of events Ayatollah Khomeini's followers want the world to believe. Their new hard line in presenting it is no more likely to be successful than their earlier approach.

Neither the expulsion of an Associated Press correspondent nor the forced closing of the Time bureau -- the Iranians were furious about the story that accompanied that magazine's selection of the ayatollah as its "man of the year" -- has had much effect on the quality of news reports from Iran. American journalists are not intimidated by such repugnant acts. Throwing out all American or all Western correspondents, however, would hardly help the ayatollah sell over here; it would simply make all the news from Tehran suspect and raise even higher the fears and foreboding Americans share about the fate of the hostages.

The shifting relationship between Iranian authorities and American reporters proceeds from a recognition by the Iranians of one of their king-sized miscalculations. The ayatollah's government had not been tolerant of foreign journalists prior to the seizing of the hostages in November. In fact, it had expelled 18 journalists between July and September for what it was pleased to call "inaccurate news reports." But after the hostages were seized, the foreign press became a weapon the Iranians thought they could use. "We need to convey our message to the world," former foreign minister Abol-Hassan Bani-Sadr said on Thanksgiving Day. "For this, we much use the media."

But "using" the media did not turn out the way the Iranians had thought it would. A message was conveyed to the American people, all right, but it was not exactly one to fulfill the ayatollah's weird fantasies of an uprising against President Carter. Mr. Carter's polls shot upward. And the blatant propaganda that the ayatollah's followers and the kidnappers dished out as the "truth" was labeled for what it was by the news media or, when that was impossible, winnowed out by the American reading and viewing public, which hasn't been looking at TV white-hat/black-hat stuff all these years for nothing and which is more than a little sophiscated at seeing through baloney on the screen and in political outpourings.

The more we think about it, the more remarkable the reporting job done from Tehran -- by newspapers, magazines and television -- appears to be. That statement by "Mary," which the kidnappers insisted American television broadcast, and those chilling Christmas pictures of hostages sitting with heads down and blank stares revealed far more about the true state of affairs than the Iranians intended them to. The American public and the rest of the world have gotten a clear picture from Iran, even if it is not the picture the ayatollah's followers mean to promote.

Despite occasional allegations, here that American journalists have interfered with diplomatic maneuvering or permitted themselves to be manipulated by the Iranians (and allegations in Tehran that they have been manipulated by Washington), the journalists have been the only direct link between the American public and Iran for more than two months. Not the least of the functions they have served has been the prevention of wild rumors about the hostages and conditions in Iran. Given the public mood in the interpreted in the way most hostile to the ayatollah. That is something to which the Iranian authorities should give careful consideration before carrying out their threat to expel all Western journalists.