LONDON – Metropolitan police hoped that the arrest of two suspects and the largely unexploded remains of four rucksack bombs would lead to a wide array of intelligence and forensic breakthroughs on both yesterday’s bombings and the ones that rocked London exactly two weeks before to the day.

Though they failed to draw any blood, yesterday’s lunchtime duds seemed more successful than the July 7 bombings, which left 52 victims and four suicide bombers dead, in sowing fear and terror in Londoners, as they reconciled themselves to the reality that homegrown terrorists are living in their midst and can strike at any moment.

“We can’t minimize incidents such as this,” Prime Minister Blair said at a news conference with the Australian prime minister, John Howard, with whom he was having lunch when the bombers struck. “They’re done to scare people, to frighten them and make them worried.”

Yesterday’s four midday attacks, though less closely timed than the early-morning bombings of July 7, were coordinated and targeted trains near the Warren Street, Oval, and Shepherd’s Bush underground stations as well as a bus on Hackney Road in east London. No one was killed, and the only reported injury was later ruled an asthma attack.

Teams of emergency personnel moved in quickly, including firefighters, police, and forensics experts. The areas where devices were found were cordoned off, and the Associated Press reported that a University College hospital was searched when staff there reported that they saw a suspicious man with wires visible in his shirt pocket.

London’s Daily Telegraph reported that at Oval, the terrorist who attempted to detonate a bomb did so while standing beside a woman holding a baby and escaped after being chased by passengers. Witnesses said that they saw white smoke in the station, the Telegraph said.

The newspaper also reported that one of yesterday’s bombers was described as being about 19 years old.

That fear was palpable in an otherwise perfect July afternoon, as the streets were thronged with walking commuters, punctuated by runners, both fit and flabby, jogging home from work with their suits and ties stuffed into briefcases and purses.

Running the seven miles from his office near the Warren Street tube stop to his home in Stoke Newington, Ant Melder, 32, seemed rather stoic about his new commute. But he dispensed with any pretext of bravado about his new routine.

“I am going to be doing this a lot more,” he said as he huffed along Guilford Street.

Throughout central London, the buses were all but spilling passengers from their doors, as many of London’s signature double-decker red behemoths bypassed large clusters waiting to board.

With three bombs setting off in the London Underground and one on a double-decker bus, the lunchtime bombings bore an eerie resemblance to the suicide attacks a fortnight ago.

Both incidents formed a “burning cross” effect, with bombs detonating in the north, south, west, and east of London. Again, the targets were three tube trains, although this time it was 12:30 p.m. instead of 8:50 a.m. when the bombers struck. That was followed, almost an hour later, by the bus bomb.

The second bombing in as many weeks was also effective in shutting down large parts of London’s underground transportation system. Immediately after yesterday’s midday blasts, which some passengers likened to the pop of a champagne cork, two underground lines were shut down until further notice, adding dozens of more stops to the list of stations that have not been operating since July 7.

It was unclear if the attack was plotted by the same terrorist organization that coordinated the attacks two weeks ago. Whether or not the terrorists were would-be suicide bombers was also yet to be determined.

“Clearly, the intention must have been to kill,” Police Commissioner Ian Blair told a news conference. “You don’t do this with any other intention.”

Police authorities held out the possibility that yesterday’s unsuccessful attempt to claim innocent lives was merely a copycat attempt.

Mr. Blair said he was confident that yesterday’s attacks might shed light on the methods and materials of the July 7 blasts. Other news reports indicated that authorities were becoming increasingly confident that the materials of yesterday’s blasts were highly similar to the first attacks and could have come from the same batch of explosives.

“We do believe that this may represent a significant breakthrough in the sense that there is forensic material at these scenes,” the commissioner said. He also noted that no chemical, biological, radiological, or nuclear agents had been found at any of the scenes.

In the case of all three tube incidents, passengers or passers-by saw men running away from the scene.

As the prime minister called for calm, Queen Elizabeth continued to host a garden party for 8,000 guests.