A bomb explosion ripped through a crowded shopping center in the Champs Elysees today, killing two persons and injuring 28 others, in an apparent escalation of a terrorist campaign against France.

Today's attack, which took place minutes after the appointment of a new conservative government, was the latest in a series of bombings by a mysterious pro-Islamic group that has called for the release of Arab prisoners from French jails.

A second bomb was defused in a crowded commuter train at the other end of Paris after a passenger noticed an unattended bag and alerted police.

The latest bombings pose a major challenge to the new government headed by Prime Minister Jacques Chirac, who has promised to take a tough line against terrorism. The outgoing Socialist government refused to give in to the demands of the terrorists, who appear to be linked to pro-Iranian organizations in Lebanon who have seized eight Frenchmen during the past year.

Demands issued by the terrorist group in France, which calls itself the Committee for Solidarity with Arab political prisoners, and the extremist organizations in Lebanon have been similar, but not identical. Both groups have insisted on the release of the leader of a five-man commando team, who is serving a life sentence following the attempted murder in a Paris street in July 1980 of former Iranian prime minister Shahpour Bakhtiar.

The explosion on the Champs-Elysees occurred as Chirac was making his first declaration as prime minister, pledging among other things to improve security and law and order. He visited the scene of the blast, accompanied by his new minister for public security, Robert Pandraud. Eyewitnesses described the scene of the blast at the Galerie Point-Show as horrifying, with bodies strewn across the sidewalk amid debris. An emergency medical center was set up in a nearby fast-food restaurant.

One of tonight's victims was identified by police as a 22-year-old French citizen of Lebanese origin, Jean Victor Guereiche. The second fatality was an unidentified man.