In an effort to limit reporting on the Americans being held as prisoners by Islamic extremists inside the U.S. Embassy in Tehran, the Iranian government has expelled all American reporters, including correspondents of The Washington Post. Using reports from those news organizations that are permitted to continue to function in Iran and from information available outside that country, The Post will continue to report the siege of the embassy, which today entered its 81st day .

The Islamic militants holding Americans in the U.S. Embassy in Tehran last night branded the embassy press attache as a spy and renewed threats to stage espionage trials for the estimated 50 hostages.

In the latest of their televised disclosures of what they claim are captured embassy documents, the captors described the attache, Barry Rosen, as "a famous spy and plotter" who tried to subvert the Iranian press.

"When we put him on trial, the plots of the United States will become more clear," said a spokesman for the radical embassy occupiers, who describe themselves as Islamic theology students.

Since they seized the 24-acre embassy compound 80 days ago, the young militants have threatened to try the American hostages as spies unless deposed Shah, Mohammad Reza Pahlvi, now in Panama, is returned to Iran.

They have not raised the threat of trial, however, since Ayatollah Ruhollah Khomeini rejected their demand two weeks ago to hand over U.S. Charge d'Affairs L. Bruce Laingen for questioning on alleged espionage documents.

While constantly referring to the embassy as "the nest of spies," the revolutionary captors have only named two Americans as espionage agents until last night. In early December, they produced purported State Department documents that they said showed that three other hostages are Central Intelligence Agency officers serving under diplomatic cover.

In last night's broadcast, a spokesman unveiled alleged documents from Rosen to the State Department that he said proved the press attache had been in contact with the editors of Iranian publications opposed to the revolutionary government.

The documents, according to the spokesman, sought the editors' cooperation to improve the image of the United States in Iran. But none of the papers showed that the editors had done more than hold general discussions about editorial policy or the financial backgrounds of their papers with Rosen, according to news reports from Tehran.

Meanwhile; recent efforts by Iranian officials to appease the nation's rebellious Kurdish minority faltered yesterday when Kurdish leaders urged supporters in their western province to boycott Friday's presidential election.

Government officials had hoped to use the nation's first political contest as a way of easing widespread regional tension in Iran and unifying the country against the perceived threat of Soviet military invasion.

But Kurdish leaders seeking local autonomy for their 4 million people remained unmoved yesterday be recent government concessions, including the withdrawal of unpopular paramilitary forces from two Kurdish cities.

Sheik Ezzedin Hosseini, a Kurdish spiritual leader of the Sunni sect of Islam, called for an election-day boycott at a mass meeting in Mahabad commemorating the short-lived Kurdistan Autonomous Republic of 1946.