The kidnaped administrator of the America University of Beirut, David Dodge, is almost certainly being held by Iranian Embassy officials hoping to exchange him for an Iranian envoy who may have been abducted earlier this month, a well-informed Lebanese Moslem leader said today.

The source, who did not want to be identified, said the Iranians evidently were holding Dodge in hope of trading him for Iranian Charge d'Affaires Mohsen Mousavi, who disappeared with three aides July 4 after entering an area controlled by the Christian Phalangist militia. Iran has accused the Phalangists of abducting Mousavi and his aides, but the rightist militia has denied any involvement.

Although the kidnapers' strategy is still unclear, it appears to be aimed at getting the United States to exert pressure to help recover the Iranian envoy.

Dodge, the acting president of the university located in besieged West Beirut, was kidnaped Monday by several gunmen as he was walking to his residence.

The kidnaping was widely denounced by Lebanese and Palestinian leaders of various factions, and the Palestine Liberation Organization said its police were joining Lebanese authorities in searching for Dodge.

According to the Lebanese Moslem leader, Dodge is being held "somewhere in Beirut" and bargaining is taking place to obtain his release. "I have good reason to believe he is alive," the source added.

The source said the Phalangists did not appear to be involved in the abduction of the Iranians, but he declined to suggest who was. According to the Phalangists, the Iranian charge's car was found in Tripoli.

The Iranian Embassy has been severely damaged and abandoned in Israeli air strikes and shelling from gunboats following the invasion of Lebanon. It is believed to be operating from the ambassador's residence in the suburb of Shiyah.

U.S. officials working at the ambassador's residence in an Israeli-controlled Christian suburb acknowledge making contacts with various groups in an effort to obtain Dodge's release.