Several times last week, police convoys bringing recently arrested Moslem militants to a Cairo court stopped in traffic near the U.S. Embassy.

Through the bars of the paddywagon, American diplomats could hear the old familiar cry, "Allahu akbar, allahu akbar" -- God is great -- coming from the inmates, whose detention had not been announced by the government.

Militant Moslem fundamentalists are on the march again in Egypt, and the first signs of a revival of sectarian discord are surfacing.

Arousing little notice or comment here, fundamentalists met on Jan. 18 in one of their old gathering places, Cairo's Mesgid Ennur Mosque, to hear a sheik recently released from prison.

To anyone here who lived through the events leading up to the assassination of president Anwar Sadat, the theme was like an echo from the past -- an attack on the recently reinstated Christian Coptic pope, Shenouda III.

Sheik Omar Abdul Rahman, a blind spiritual leader of Jihad, a Moslem extremist group, was speaking passionately to a crowd of 1,500 followers after Friday prayers. Soldiers who were members of Jihad or one of its offshoots shot and killed Sadat during a military parade on Oct. 6, 1981, and then a few days later staged a day-long uprising in Assyut, in which 87 persons were killed.

Why, demanded Rahman, was the Christian pope allowed back in the pulpit to preach when Rahman and other sheiks accused of extremism but cleared by the courts were not? Why had the pope received so much publicity upon his release when Rahman and other sheiks were ignored, along with their demands for the application of the sharia, the Moslem law, in Egypt?

Another sheik, Hafez Salama, told the crowd that freeing the pope without a court passing judgment on the charges Sadat had leveled against him was "illegal."

A leaflet handed out at the prayer service decried the release of the pope, calling him "the head of sectarian strife" and decrying that the fact he was "hailed by the state and returned to his papal seat."

The thrust of their speeches and the site -- the half-finished mosque, just a half-mile from the main Coptic cathedral -- were disturbing signposts out of recent Egyptian history. It was there that western reporters went to test the mood of the rising Moslem extremist anger in the summer and fall of 1981 and to watch demonstrations begin.

Since the end of the trial of 302 Jihad members last September, Moslem militants have again been coming out into the open, and in numbers.

They are active and well organized on the university campuses, old strongpoints, and they made a strong showing in December elections, capturing the majority of student council seats at the engineering faculty of Cairo University. Often they appear clean-shaven and dressed in European-style clothes, instead of their usual beards and white robes, to avoid the watchful eye of university plainclothesmen.

At street corners in downtown Cairo and at busy traffic stops, bearded men dressed in white are again appealing through bullhorns to passersby for donations to build new mosques.

On rear windows of cars, the shahada, the basic Islamic religious declaration -- "There is no deity but God and Mohammed is his prophet" -- is more and more in evidence. The Copts, for their part, are displaying stickers of Pope Shenouda and Christian religious verses.

Shenouda, recently released from banishment to a desert monastery, already has given interviews that even some Christians say they regard as verging on the political and as unnecessarily provocative.

So far, there have been no reports of any incidents between Moslem and Coptic militants. But the release of Shenouda and the revival of Moslem militant activities seem to be setting the stage for sectarian trouble.

It already has started again between Moslem militants and security forces, however. In mid-November, students at the Islamic Al Azhar University rioted and clashed with thousands of Central Security Force police -- a special urban antiriot force -- after a student was killed in a hit-and-run accident by one of the unit's officers. Several hundred students were detained during four days of demonstrations.

The students initially demanded only that the officer be arrested and put on trial. But by the time the demonstrations were over, the university had to be closed for two weeks and students were demanding that women be obliged to wear Islamic dress and that the sharia become the law of the land.

Moslem militants are not the only group becoming active again. On Jan. 10, a court sentenced six alleged Communists to prison terms of up to five years for illegal possession of arms and explosives. Ten others were acquitted because the government failed to prove they were part of an underground Communist cell.

Nine days later, in an interview with a local newspaper, Interior Minister Ahmed Rushdi disclosed that police had arrested 25 leftists found in possession of antigovernment leaflets urging Egyptians to join demonstrations and strikes.

On Jan. 21, police arrested 22 alleged Trotskyites and Communists in towns and cities throughout Egypt and charged them with inciting riots and distributing leaflets exhorting Egyptians to "armed struggle." The same night, security forces in Zamalak, an upper class suburb on a Nile River island in the middle of Cairo, exchanged shots with someone fleeing in a car -- the first gunfire heard there in years.

The government, in the view of observers, seems to be girding itself for the revival of political activities on both the right and left. Security forces have been beefed up and both westerners and Egyptians note increasing evidence of heightened vigilance -- although some of it may be directed at possible subversion from neighboring Libya. There are more police checkpoints on the streets of the capital at night, and Egyptians out after midnight are sometimes stopped and asked for identification.

On the outskirts of Cairo, on the road to Ismailia, the large barracks of the Central Security Force are steadily being expanded to make room for more recruits.