A powerful car bomb exploded inside the French Embassy compound here today, killing at least 11 persons in the bloodiest attack so far in a series of terrorist strikes against French interests in Lebanon.

The blast, which Lebanese security officers said was detonated by remote control, sent a gush of white flame out the compound gates into a line of visa applicants waiting on the sidewalk and a street full of cars and pedestrians on their way to work, witnesses said.

It killed five embassy employes, including a security guard and the driver of the car, a secretary who apparently was unaware it contained a bomb, and it left the area strewn with detached limbs lying among the rubble.

The other victims were Lebanese passers-by or people who had come to the embassy on business. The French ambassador, Paul Marc Henri, is in Paris for consultations.

The bombing, which police said also injured more than 25, pointed up the dangers facing foreign diplomats in this city where normal standards of law and order have vanished in a maze of competing Lebanese militias, Palestinian guerrillas and Syrian truce-keeping forces.

At least 30 diplomats have been killed since civil war broke out in 1975, but French interests have been a particular target in the past nine months.

In Paris, a Foreign Ministry spokesman said France would keep its Beirut embassy open despite the attacks, Reuter reported. "We shall increase security measures for the personnel at the embassy," the spokesman added.

French officials have linked the attacks against their countrymen to a dispute between France and Syria that broke out in public after charges by high French officials that Syrian agents played a role in the assassination here last September of French ambassador Louis Delamare.

The charges, which have been attributed to French Foreign Minister Claude Cheysson, come against a background of increased French friendship with Israel since President Francois Mitterrand took office a year ago. But, French officials have said, they stem mostly from a French investigation that showed Syrian truce-keeping troops were manning a checkpoint near the spot where Delamare was killed.

Syria has denied the charges, and in the shadowy world of Beirut's frequent bombings concrete evidence rarely surfaces. Some Lebanese security sources have suggested France's role in trying to solve the Lebanese conflict led Syria to order Delamare's killing. But others have said Syria had nothing to do with it, blaming instead Iranian radicals with unofficial Lebanese or Syrian connections who are eager to punish France for offering refuge to Iranian exiles.

Whatever the motives, French citizens have been repeated targets of violence and French officials have directly and indirectly pointed fingers at Syria.

On April 15, a French Embassy employe, Guy Cavallo, was killed along with his wife in their Beirut apartment. At the time, Henri publicly speculated that the international terrorist known as "Carlos" could have been linked to the killing.

Carlos had threatened to attack French interests unless two of his associates were released from a French jail. At the same time, radical Palestinian officials said Carlos was working with Syrian intelligence agencies. There has been no substantiation of any of the speculation about Carlos, however.

Syrian officials, including President Hafez Assad, denied any connection to the anti-French violence. A French television film nevertheless strongly suggested that Syria participated in the Delamare slaying. It was aired April 21. The next day a bomb exploded in front of the Paris offices of Al Watan al Arabi, an anti-Syrian magazine, and France expelled two Syrian diplomats.

Last month a French officer in the U.N. Truce Supervisory Organization was killed on a Beirut street in what French diplomats said was a car theft. In addition, the offices of Agence France-Presse, the French news agency, have been bombed.

Most Arab ambassadors have fled, leaving only emergency staffs. European embassies also have reduced their personnel. The British Embassy decided this month to leave only a skeleton crew here after a British diplomat's wife was raped by three gunmen.

U.S. Ambassador Robert Dillon directs a shrunken staff under tight security. A U.S. military attache, Col. Fred Hof, was shot in the shoulder last month, but an embassy spokesman said today there are no plans for Americans to leave.

Today's explosion killed a French paratrooper, part of a beefed-up guard brought to the embassy recently, and Anna Cosmides, the French employe whose car was rigged with the bomb, apparently without her knowledge, embassy spokesman Rene Janier said. In addition, it killed three Lebanese employes of the embassy--a plumber and two messengers, he said.

Janier said embassy officials had no idea who was behind today's bombing. Callers to news agencies claimed responsibility on behalf of two groups--the Moslem Holy Warriors and the Free Nasserite Revolutionaries. The groups had never been heard of before and authorities did not take the calls seriously.

Cosmides was a French citizen of Greek origin who has worked at the French Embassy here for many years. Lebanese security officials said the bomb was under the rear seat and was detonated by remote control just after she was waved inside the high-walled compound by gatekeepers who knew her well.

The explosion propelled her car 30 yards toward the stone embassy, reducing it to a compact tangle that came to rest in a flower garden under the flagpole. The embassy building was only slightly damaged, but offices and shops on the other side of the street were shattered by the force of the blast.

Lebanese security officers speculated that the bomb was placed in the car during the night, when it was parked outside Cosmides' apartment about half a mile from the embassy in mostly Moslem West Beirut.