JERUSALEM (AP) _ Israel wants information on its missing servicemen before entering into any negotiations on a possible hostage exchange in Lebanon. But getting this information might prove a lengthy and complicated process.

It involves contacting various organizations - Shiite and Palestinian - and the governments of Syria and Iran. Israel wants a videotape or other solid evidence on the status of the seven Israelis before it releases any Arab detainees.

One military analyst said disagreements between rival factions believed to be holding some of the Israelis could prevent this information from getting out and ''explode the negotiations overnight.''

The most difficult part, however, concerns three soldiers who disappeared in a tank battle with Syrians during the 1982 Lebanon invasion. They are Sgt. Zachary Baumel, Sgt. Zvi Feldman and Cpl. Yehuda Katz.

They disappeared in June 1982 near the Bekaa Valley town of Sultan Yacoub, an area where Syrian, Palestinians and reportedly Libyan troops were facing the Israelis. Nobody has admitted holding them in captivity.

This has not discouraged Yona Baumel, Zachary's father, and as far as he is concerned his son, Feldman and Katz are still alive and being held somewhere.

''We have some pretty solid information that it's one of the pro-Syrain Palestinian groups who is holding them,'' Baumel said in a telephone interview.

He was optimistic that the Syrians had enough influence over the group to encourage them to release some signs of life.

Israel cannot afford to take anything for granted. Following the 1973 Yom Kippur War, Syria took months until it released a list of Israeli POWs it was holding. Some of those included troops who had been previously considered killed in action.

Getting information on the remaining soldiers might be easier since they have been claimed by various groups.

Sgt. Samir Assad was kidnapped in Sidon in 1983 and was held by the Marxist Democratic Front for the Liberation of Palestine. They said he was killed in an Israeli air raid and have repeatedly offered to swap his body for Palestinian guerrillas. Israel wants proof the body is that of Assad.

Two Israeli soldiers, Pvt. Joseph Fink and Pvt. Rahamim Alsheikh, were kidnapped during an ambush in southern Lebanon in 1986 and are believed to be held by pro-Iranian Hezbollah movement.

Even if it turns out some of the soldiers are dead, it is important for Israel that their remains be brought back for a proper Jewish burial on Israeli territory.

It is reasonably certain that air navigator Ron Arad is alive. He was shot down while on a bombing mission in southern Lebanon in 1986 and was claimed captured by the Shiite Amal organization.

His wife, Tami, repeatedly said he is held by ''Iranian soldiers.''

Ron Ben-Yishai, military analyst for the Yedioth Aharonoth newspaper, said there were rival groups within both the Hezbollah and Palestinian camps who were clashing with each other over conditions to release information on the Israeli captives.

''Some want this price, some want another. All these things could explode the negotiations overnight,'' Ben-Yishai told army radio. ''The beginning is very pretty but the continuation is very vulnerable and fragile.''