U.S. Capitol Police Chief Terrance W. Gainer has taken several aggressive steps in recent months to heighten security around the Capitol, including retraining officers to shoot a suspected suicide bomber in the head if other efforts to stop an attack fail.

Gainer's decision Monday to close a major thoroughfare and impose 14 vehicle checkpoints on Capitol Hill was one piece of a much larger security strategy, which has included intensive training with Israeli counterterrorism experts and bomb technicians.

In addition, Gainer said he is urging congressional officials to create a "virtual fence" that would allow his officers to search any person who steps onto the Capitol grounds, a significant expansion of current policies on searching visitors.

The decision to restrict traffic drew criticism from city officials who said it would cause gridlock and send the wrong message to tourists and residents. That debate may foreshadow an even tenser exchange over how much to curtail public movement in the name of security.

"We are trying to present ourselves as the capital of the free world . . . and lead by example," said Rep. James P. Moran Jr. (D-Va.). "To have the right to search anyone whenever they step on the Capitol grounds, when they don't even try to enter a building, is overreaching."

Rep. Thomas M. Davis III (R-Va.), chairman of the House Government Reform Committee, which oversees the District, agreed that new restrictions would be a nuisance. "I can't overstate the inconvenience this is going to be to people who want to do business at the Capitol," he said.

But Davis defended the measures, including the expanded searches, as necessary. "We had two police officers killed," Davis said, referring to the slaying of two Capitol Police officers in 1998. "We've got a number of threats going on. People who don't want to be searched don't need to come on Capitol grounds."

For some time, Gainer said, he had contemplated closing part of First Street NE, which runs between two Senate office buildings. When Homeland Security Secretary Tom Ridge on Sunday raised the threat level in Washington to orange, Gainer and several congressional leaders seized the opportunity to close the road. Gainer said he knew the plan would spark heated debate.

"Given the recent specific threat information, the bombings in Madrid and the warning about election threats, now is the moment to try to prevent a catastrophic event," Gainer said. "We need to be proactive."

Several federal law enforcement officials who work in counterterrorism, along with many others who work on Capitol Hill, said they believe that the Capitol was a target of the Sept. 11, 2001, hijackings and is still a prime target for terrorists. That belief, along with anthrax and ricin attacks on Senate offices, has frayed the nerves of many who work and live on Capitol Hill.

Since he became chief of the Capitol Police in 2002, Gainer, who is responsible for the security of the 535 members of Congress, has focused on what additional security measures could be instituted, he said.

In December 2002, he and several of his top commanders traveled to Israel with D.C. Police Chief Charles H. Ramsey, other police chiefs and FBI officials to receive training on how to prevent and respond to suicide bombings. The trip was arranged by the Police Executive Research Forum, a training and research group.

Gainer sent other members of the Capitol Police force to Israel for instruction and began retraining officers here using Israeli counterterrorism techniques. Last month, the head of the Israeli bomb squad traveled to Washington for a second time to meet with Gainer and Capitol Police officers.

In the past six months, Gainer issued a "general order" instructing officers on steps to take when confronted with a possible suicide bomber. If the suspect appears to be carrying explosives and refuses to stop and be searched or to cooperate otherwise, officers are instructed to shoot the suspect in the head.

Under standard law enforcement training, officers are told to take "center mass body shots" if they have to use their guns. But Gainer said that police have to change tactics if faced with a terrorist.

"The use of deadly force under any circumstances is the last resort," Gainer said. "But if a suicide bomber is loaded with explosives, a gunshot wound to center mass wouldn't be prudent. You need to take a head shot."

In the spring, Gainer faced resistance when he advocated erecting a fence around the Capitol, an idea that had been proposed five times since 1985. He argued that the Capitol, a preeminent symbol of American democracy, should be protected in the same manner as the White House. The White House has a wrought-iron fence ringing the grounds, and the street in front of it is closed to traffic.

The idea drew conflicting reactions from the leaders of the House and Senate, and no action was taken.

Gainer's proposal of a virtual fence of security around the Capitol would permit searches of packages and people anywhere on the Capitol grounds. Currently, visitors to the Capitol go through metal detectors and can be searched if they enter any of the buildings.

Capitol officials said yesterday that even before Sunday's announcement, they had planned to shut First Street between the Russell and Dirksen Senate office buildings this month.

"We were going to do that anyway," said Senate Sergeant-at-Arms William H. Pickle. "It was just a coincidence they raised it about the same time."

Several streets near House office buildings have been closed for years. Gainer said he has been increasingly worried about First Street in light of "blast studies" of the damage that could be caused by a car or truck bomb in such a tight space.

"A car with a 2,000-pound bomb concealed in the trunk would do substantial damage structurally, as well as cause thousands of deaths," he said. "Most of the post-9/11 discussion was, 'Why weren't you guys in law enforcement doing something on 7/11 or 8/11?' We're at the vortex here. We think this is a thinking man's way to approach this."

Staff writers Helen Dewar and Spencer S. Hsu contributed to this report.

Supreme Court Police Cpl. Frank O'Neill checks identification on Second Street NE. Reaction to recent steps to increase security in the city has been mixed.On First Street NE, a U.S. Capitol Police officer gets off a Metro bus after conducting a walk-through inspection at a security checkpoint.