In the month since the first bombings of London's transit system, the British prime minister has unveiled extensive new anti-terrorism laws while security agencies have carried out what is widely described as their largest mobilization since World War II.
Across the Atlantic, the response has been far more restrained, with few signs of increased U.S. readiness except in major transit systems.
The difference is certainly due in large part to the fact that the United Kingdom, not the United States, was the target in two attacks last month. But the quieter mood also reflects a growing recognition among U.S. counterterrorism officials and the public that it is exceedingly difficult to thwart plots like those in Britain, which were apparently carried out by isolated terrorist cells with raw materials that could be obtained at a beauty shop or supermarket, according to U.S. government officials and terrorism experts.
The FBI and other U.S. intelligence agencies also continue to say they have no specific evidence that al Qaeda or affiliated groups are planning any such attacks in the United States. That finding has been noted repeatedly in recent public statements, congressional testimony and bulletins distributed to U.S. law enforcement agencies.
"We've done most of the obvious things that you can reasonably do" to guard against terrorist attacks in the United States, said Brian M. Jenkins, a terrorism expert at Rand Corp. "At the same time, there is recognition that with limited resources we're going to have to move away from a notion of trying to provide 100 percent security and toward risk management. That's a whole different mind-set."
Immediately after the first London attack on July 7 -- which killed 56, including the four presumed bombers -- the U.S. Department of Homeland Security raised the terror threat level for transit systems to "orange," or high risk. Washington and other major cities increased spot-checks on trains and added patrols of armed and plainclothes police, while authorities in New York implemented a controversial system to randomly search bags of subway passengers.
The FBI also increased staffing at its command center in Washington and aided British investigators by providing information on suspects with links to the United States and interrogating al Qaeda members in U.S. custody for clues to the bombings. Joint intelligence bulletins issued last month by the FBI and Homeland Security said that al Qaeda and other terror groups remained interested in mounting suicide attacks on passenger trains and other targets in the United States.
But one of the bulletins, first reported by the New York Times yesterday, also noted that authorities "have no recent information indicating that attacks similar to the London bombings are planned for the United States."
Brian Roehrkasse, a Homeland Security spokesman, said, "We do not have any credible or specific evidence indicating a possible attack of the kind seen in London."
The lack of specific information leaves U.S. authorities to closely analyze the evidence coming out of the highly secretive probe in London. In a meeting with corporate security officials this week, New York City Police Commissioner Raymond W. Kelly warned that the strategy used by the bombers in London could easily be transferred to New York.
Kelly and other New York police officials said that British investigators have concluded that the explosives used in the July 7 attacks were made by hand from common items such as bleach and food preservatives and that the materials were stored in commercial refrigerators in a tenement apartment in the city of Leeds. The explosives, made of a compound that breaks down at room temperature, were transported to the outskirts of London in common beverage coolers. Similar compounds were used in the attempted attacks on July 21, the officials said.
British police have arrested 17 people, including the four suspects in the July 21 incidents and others alleged to have aided them.
The biggest worry for the FBI and other U.S. agencies is that the type of plots carried out in London are particularly difficult to detect ahead of time, especially if the operatives are not directly connected to leaders of al Qaeda or its affiliates.
"These individuals may be essentially acting on their own, with no real command and control from people that we may be aware of," one FBI official said this week. "There are very few indicators that allow you to pick up on a team or teams like this."
Investigators in Britain and their U.S. counterparts are also still struggling to determine whether the two London bombing attacks were directly connected.
"All they've got so far is that people from cell one and cell two were in Pakistan at roughly the same time," said one U.S. source, who like others declined to be identified, citing British officials' insistence on secrecy.
Initially, officials were relying on evidence from the crime scenes and the homes of some of the suspects. But with more than a dozen people now in custody, interviews with the suspects and their accomplices are providing the best leads.
An Egyptian chemist who was arrested in Cairo after the first attacks is still being held, but officials said he is less of a concern than was originally thought. That is also believed to be the case with Haroon Rashid Aswat, a British national arrested in Zambia who is wanted by the FBI in connection with a plan to set up an al Qaeda training camp in Oregon.
The sheer number of possible conspirators willing to help or cover for the would-be bombers is alarming and only exacerbates the difficulty in identifying such cells ahead of time, U.S. officials said.
Staff writer Dafna Linzer contributed to this report.