A car bomb exploded on a street in Christian east Beirut today, killing at least three persons, and witnesses said four members of a French television crew were kidnaped as the underground Islamic Jihad threatened to kill a French diplomat seized here a year ago.

The blast shattered glass and gutted storefronts in the Jetawi quarter but caused no damage to a Phalangist Party office that apparently was the target.

Officials at the Greek Orthodox hospital said they had received three dead and about 40 wounded from the explosion. Local radio stations said five persons had been killed.

No one took responsibility for the bombing, which observers said appeared to be a continuation of conflicts between Christian groups over a controversial, stalled peace pact brokered by Syria.

The witnesses said the four Frenchmen, with France's Antenne 2 television station, were seized by gunmen in west Beirut. No group asserted responsibility.

The bombing was the sixth in east Beirut this year. It coincided with a Vatican mission aimed at studying Christian grievances, a formula for coexistence with Lebanon's Moslems and possible mediation with Syria.

Earlier today, an anonymous caller claiming to represent the radical Islamic Jihad faction said his group was contemplating killing either Marcel Carton or Marcel Fontaine, two French diplomats seized in Moslem-controlled west Beirut last March 22.

The caller told two western news agencies that the life of one of the Frenchmen was endangered unless France met two new demands: return of two Iraqi opposition members deported to Baghdad after a series of bombings in Paris last month and assignment of Dr. Razah Raad as sole mediator in the dispute.

Raad, a Lebanese Shiite Moslem heart specialist, has been in contact with the kidnapers before and delivered letters from the French captives to their families last fall.

Three days ago Islamic Jihad sent a statement to news agencies saying it had killed French researcher Michel Seurat, kidnaped here last May. No body has been found, however.