The disappearance of one of Lebanon's most prominent religious leaders has provoked grief and outrage among his followers and ignited an international dispute about what happened to him.

The Imam Musa Sadr, 50, spiritual leader of nearly a million Shiite Moslems in Lebanon, was last seen in Tripoli, Libya, on Aug. 31.

Libyan officials say he took a flight to Rome that night. It has been confirmed that his name was on the passenger list of an Alitalia flight on that date, but authorities in Italy say there is no proof that the Imam actually left Libya. There is no record that any traveler bearing that name entered Italy, but if it was the Imam he could have used Rome airport as a transit point to some other destination.

The Shiites believe he never left Libya. Prominent members of the Shiite community here and in Iran have charged that he was arrested on orders from Col. Muammar Qaddafi, the Libyan leader. They say Qaddafi viewed the Iman as a threat to his own aspirations to a position of religious leadership among the world's Moslems.

The disappearance of the Imam has predictably added to the tensions afflicting Lebanon, a country that seems destined to lurch from one crisis to another. The Higher Shiite General Council organized a general strike Friday to demand the return of the Imam. The strike shut Moslem West Beirut and several other towns, and the council said that would be only the "first step."

Thousands of posters showing the imam's bearded face have been plastered on walls and automobiles around the country, asking where he is. At the Shiite council headquarters, on the coast south of Beirut, groups of men, some of them armed, have been meeting to consider their next move.

An investigating team sent to Tripoli and Rome by the Lebanese government returned last night with no new information.

Dr. Omar Misseikeh, the Cabinet secretary who headed the inquiry, said he had been assured by the second-ranking leader in Libya, Maj. Abdessalem Jalloud, that Sadr left Libya on the flight to Rome, but there is no trace of him in Italy.

The Shiite branch of Islam, which differs from Sunni Islam in its beliefs about the succession to the prophet Mohammed, is centered in Iran.

That has prompted speculative reports in some Arab newspapers that Sadr, who was born and educated in Iran and has a reputation as an opponent of the shah, had traveled secretly to Iran to join Shiite unrest against the imperial rule.

That theory is rejected absolutely by the Shiite leadership here.

The Ayatollah Shraiat Madri, one of the most prominent Shiite figures in Iran and a leading opponent of the shah, sent a telegram to Qaddafi saying, "The whole world knows the imam was invited to your country and that he went there. Since then, there has been no news of him."

He sent copies of his telegrams to Presidents Houari Boumedienne of Augeria, Elias Sarkis of Lebanon and Hafez Assad of Syria, saying the responsibility for Sadr's disappearance lies with the Libyans.

Christian newspaper here have suggested that Qaddafi arrested the imam because of a dispute over what use had been made of money the Libyan leader had given him to finance political activity among the Shiites of southern Lebanon.

That theory is indirectly supported by Shiite officials who confirm that on an earlier trip to Libya, the imam had quarreled with Qaddafi over two issues - the role of Shiites, traditionally the most backward and least influential of Lebanon's religious groups, in the country's Moslem-Christian struggle, and Qaddafis religious views.

It is known that Sadr was invited to attend ceremonies marking the anniversary of the Libyan revolution on Sept. 1. He accepted, and traveled to Tripoli on Aug. 25 with two companions, Sheik Mohammed Yacoub and Abbas Badreddin, a journalist. All three vanished on Aug. 31.

Shiites who believe the imam is still in Libya point out that if he had gone to Rome on Aug. 31, as the Libyans say, that would mean he left before the ceremonies that were the reason for his trip.

But if Qaddafi really wanted to get rid of Sadr, as some Shiites believe, he could have done so under much less embarrassing circumstances.

The imam, who studied theology in the Iranian holy city of Qom and secular law at Teheran University, came to Lebanon in 1960. He gained great popularity by his energetic work for the material and social benefit of the Shiite community, promoting the establishment of clinics, schools and sports centers among the Shiites, who traditionally had been cut off from most of the political and economic power of the country.