More than 75 Iranian supporters of Ayatollah Ruhollah Khomeini were arrested in front of the Iranian Embassy here yesterday while another 150 marched or sat in silent protest against the embassy, now controlled by Iranian soldiers loyal to Shah Mohammad Reza Pahlavi.

The peaceful, wordless and strangely slowmotion protest occurred in the late afternoon, clogging rush hour traffic along Massachusetts Avenue, NW as police threw a heavy guard around the ornate embassy building at 3005 Massachusetts Ave., just west of Rock Creek Park.

Those arrested -- 56 men and 20 women -- were charged with blocking the sidewalk in front of the embassy.

The remaining protesters -- mostly young Moslem students -- sat in silence on the sidewalk just east of the embassy, huddling together to stay warm.

Some periodically stood up and bowed or kneeled in prayer, removing their shoes and even their socks.

With nightfall, companions brought food and blankets to the protest group -- now down to about 100. Heavily armed D.C. police and both uniformed Secret Service officers and plainclothes agents watched them warily until they dispersed last night.

The heavy ornamental doors of the embassy remained shut, and there was little traffic in or out of the building.

Military officers took over control of the embassy Wednesday, ousting charge d'affaires Assad Homayoun and restoring the shah's portrait in the embassy lobby -- yet another ripple in the confusing sea of Iranian politics.

In addition, it was learned from reliable sources that Iranian Ambassador Ardeshir Zahedi -- longtime ally of the shah -- returned to Washington yesterday from Morocco where the shah has been officially "vacationing" during the trubulence in Iran. Zahedi's return appeared to strengthen further the shah's control of the embassy here.

The protesters outside the embassy yesterday generally would not talk to reporters or explain why they were protesting. "I don't speak English," said one. "We don't know why we're here," said another.

But police officials said many of the participants had been seen demonstrating earlier in the day at the White House in support of Khomeini and against continued U.S. presence in Iran.

One protester told The Washington Post, "We are here to protest the people inside the embassy because they are illegal."

Their evasiveness may be explained in part by a novel agreement made by police officials and the protesters' lawyers at the scene.

Police originally intended to charge the protesters with violating the so-called "500-foot law" prohibiting demonstrations closer than 500 feet to an embassy. But the protesters were neither chanting nor singing and carried no banners, placards or other outward signs of their protest.

D.C. police legal advisers at the scene recommended that police stop the arrest procedure and change the charge against those already arrested to "incommoding" -- blocking the sidewalk -- since the protesters' action did not appear to meet all the legal criteria of a demonstration.

Police officials then consulted with protest lawyers and agreed to let the rest of the protesters remain on the sidewalk as long as they left a portion of it open for pedestrians.