2 Bombings Echo in Nervous Paris : France: Extra police search in subways, check identity papers. Wary tourists avoid landmarks.

On a sunny, breezy summer’s day, the kind tailor-made for tourists, James and Kate Lunt planned to take their two daughters to the Arc de Triomphe, Napoleon’s homage to his French army. But, after reading the paper Friday, they changed their minds.

“We’re going to Sacre Coeur,” said James Lunt, 43, of Greenfield, Mass., as he led the family, all dressed in shorts and tennis shoes, through the Paris streets. “I suppose the chances are astronomical that something could happen again at the Arc de Triomphe, but you have to be careful. This is not going to go away.”

All across this lovely capital, populated these August days primarily by tourists, the repercussions of two terrorist bombs, one July 25 and another at the Arc de Triomphe on Thursday, were being felt Friday.

More than 17,200 police officers, 6,000 more than usual, searched bags on the subways, checked identity papers on the streets and peered into suspicious parked cars. Several subway trains were halted by bomb scares.

The show of force, though, did not do much to assuage the fears.

For tourists, as well as Parisians, the second bomb Thursday, which injured 17 people, 11 of them foreigners, destroyed all hope that the subway bomb three weeks earlier, which killed seven, was an isolated incident. And it was becoming clear from the timing and placement of the bombs that tourists, and the city’s important tourism industry, are the targets.

“No one can say with certainty that we’re in the middle of a series of attacks,” Paris Mayor Jean Tiberi told French television. “But that doesn’t stop all of us from being afraid that it’s true.”

The mayor urged people in Paris not to fall into the “psychosis of fear that the terrorists want to create.”

Police said Friday that there are strong indications that the two bombs, both built on butane canisters of a type used commonly for camping stoves, are linked. The bomb Thursday, though smaller, was packed with bolts and three-inch nails, apparently designed to cause greater injuries.

Authorities continue to say the most likely perpetrators of the attacks are Islamic militants from Algeria, angered over French government support for the military-backed government there. Earlier this summer, police had confiscated a videotape from supporters of the Armed Islamic Group, the most radical organization operating in Algeria, which apparently was used to train guerrillas to make bombs of butane canisters.

Since last month’s blast in a subway car in central Paris, police have jailed 160 alleged Islamic extremists and questioned tens of thousands. Trash cans in the subway system as well as 300 of the 20,000 cans on city streets have been sealed.

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Nevertheless, the bomb Thursday was planted in one of the open trash cans near the famed Champs Elysees avenue. And police were considering sealing more of the trash cans.

“I thought about it today,” said Ronnie Silverstein, a businessman from Annapolis, Md., in town with his wife, Rachelle, on their first trip to Paris. “We don’t want to be in any open areas.”

But, he added, “You can’t stop it. This is a big town. I’m sure there’ll be more of these things. There’s a trash can right over there. It would certainly make me think twice about coming back.”

Authorities have good reason to suspect that the bombs have been intended to drive away tourists. The July 25 blast was in a commuter train beneath the Notre Dame cathedral and a Left Bank area thronged with tourists. The bomb Thursday was planted just across the traffic circle from the 160-foot-tall Arc de Triomphe, one of Paris’ more popular tourist sites.

A respected Algerian newspaper reported before the first blast that the Armed Islamic Group intended to step up its bombing campaign. In the past, the organization has targeted foreigners as well as intellectuals and journalists in Algeria, in its attempt to force the Algerian government to step down.

The group had vowed to avenge the deaths of four of its operatives, who were killed by French commandos on Dec. 26 after hijacking an Air France plane with 169 people on board two days earlier in Algiers and flying it to Marseilles. French police say the hijackers had intended to blow the plane up over Paris if France refused to end its support for the Algerian government.

Police believe the Islamic group’s activity in Paris may have begun even earlier last month with the assassination of a moderate Islamic cleric in his Paris mosque.

The terrorist wave in Paris is the first on French soil since 1985-86, when Iranian-backed Lebanese terrorists, demanding the release of their jailed supporters, staged a series of bombings that killed 13 people here.

French government officials are clearly worried about the growing prospect that Islamic guerrillas have declared war on the city.

Interior Minister Jean-Louis Debre said Friday that, while it was too early to establish a definitive link between the bombs, “there are a certain number of troubling elements” connecting the two. Among those are the similar types of bombs, the selection of symbolic locations for the detonations and the timing. Both occurred shortly after 5 p.m., one of the busiest times on Paris streets.

Debre called the extra police officers to duty Friday and met with the heads of Paris airports and train stations. “Today,” he told them, “I think that three words represent our approach: vigilance, sang-froid [composure] and responsibility.”