BEIRUT, Lebanon (AP) _ Gunmen killed a pro-PLO politician and a Moslem army officer in separate attacks Thursday, and the wife of a kidnapped 85-year-old Frenchman appealed to his captors to be ''gentle and caring.''

Christian and Moslem militias fought a three-hour battle using mortars, rocket-propelled grenade launchers and machine guns across Beirut's three-mile dividing Green Line. Police said the fighting killed one civilian and wounded seven others.

Camille Sontag, a retired car dealer, was kidnapped Wednesday on a crowded Beirut seaside boulevard. The same day, abductors grabbed 36-year-old Nabil Matar, a Lebanese Christian and associate professor of cultural studies at the kidnap-plagued American University of Beirut.

Police Chief Maj. Gen. Osman Osman told The Associated Press on Thursday his investigators were unable to discover any clue about the fate of either kidnap victim.

Sontag's wife, Blanche Emmanuelle, also 85, appealed to her husband's captors Thursday to be ''gentle and caring because he is so old and half-deaf and needs a hearing aid.''

Earlier Thursday, four or five gunmen in a white station wagon intercepted army Maj. Ibrahim el-Far, a Sunni Moslem, as he drove to work through Moslem west Beirut's Bourj Abu Haidar neighborhood.

Police said el-Far, 44, was forced out of his blue Renault and bundled into the assailants' station wagon. The gunmen sped off firing furiously in the air to cover their escape.

El-Far's body was found an hour later at the seaside Normandi neighborhood near the bomb-ravaged Beirut seaport, police said. They said he had been shot three times in the head and once in the right hand.

Other ambushers sprayed the black Cadillac of Nassib Khatib with automatic rifles as he drove across the town of Mdeirej in the Syrian-controlled central mountains at daybreak Thursday. Police said he was killed along with three bodyguards.

Khatib was a founder of the pro-Syrian Arab Democratic Party and its Arabian Red Knights militia. He quit in 1980 and since has been aligned with Yasser Arafat's Palestine Liberation Organization, an arch foe of Syria.

El-Far was the third Sunni Moslem officer with the army's Intelligence Department to be attacked in Beirut's Moslem sector in a month.

The Army Command said in a communique that el-Far's killing was ''part of a conspiracy hatched to sabotage the army's image as the potential standard- bearer of west Beirut's population.''

Police said the attacks suggest a Moslem militia in west Beirut is hunting down Sunni officers of the 37,000-strong Christian-commanded Lebanese army because the officers favor a return of the regular force to the western sector of the capital.

Druse and Shiite Moslems wrested control of west Beirut from the army in February 1984.

The American University suspended classes at midday Thursday and about 200 professors, staff and students held a silent march on campus to protest Matar's kidnapping.

Most of the university's Western professors have fled west Beirut since the body of a kidnapped American librarian and two kidnapped Britons were found outside Beirut last month. A note said they were killed in retaliation for the U.S. air raid on Libya April 15.