The explosion today went off under a seat in the second car of an inbound commuter train on Line C of the R.E.R. commuter regional express network at 7:06 A.M., just after the train had pulled out of the stop under the museum at Orsay, a former railroad station on the Seine that is now one of the most popular tourist sites in Paris.

Before the train reached the nearby St.-Michel station, passengers said they felt a powerful blast, and the tunnel filled with smoke as the train ground to a halt. "There was nothing but smoke and the smell of gunpowder," one survivor told French television. "I saw at least three or four people on the tracks who were gravely injured."

The bomb, made of a gas canister for camping packed with heavy metal parts, was of the same design as seven others thought to have been planted by sympathizers of the Armed Islamic Group. The Algerian Government refused to recognize a victory by an Islamic party, the Islamic Salvation Front, in elections there four years ago.

As hundreds of police officers converged on the center of Paris, a few hundred yards from where a nearly identical bomb on an underground train killed 7 people and wounded 86 in the first such attack on July 25, Mr. Juppe came to the scene. Later he addressed the French National Assembly.

At least one man was thrown out of the lightweight stainless steel car onto the tracks, but the motorman alerted oncoming trains to stop and soon hundreds of French fire brigade and emergency personnel were swarming over the scene, evacuating the wounded and others through the museum station. Two of the most seriously wounded victims, both men, lost limbs in the explosion, said to a doctor on the scene.

Most tourists were not directly affected by the early morning attack. "We came down from our hotel to go to Versailles on the train this morning, but when we got here the police were blocking the way," said Stuart Pulvirent, from Short Hills, N. J., who came to Paris with his wife, Jill, on what he described as a "spur of the moment trip."

"Jill asked me, 'What about those bombs?' " Mr. Pulvirent said. "But we didn't really think anything about it until today. I work at the World Trade Center in Manhattan, and when the bomb went off there we hit the floors."