Across the United States, thousands of houses of worship beefed up or requested information about security after last month's terrorist attacks on America -- a matter made more urgent this week, when the United States and Great Britain began airstrikes against targets in Afghanistan.

In particular, many cathedrals, mega-churches (those that regularly draw more than 1,000 worshippers), large mosques and synagogues have taken extra precautions.

"We've seen an increase in requests," said Jeff Hanna, executive director for the Guide One Center for Risk Management in Des Moines, Iowa, which represents 48,000 houses of worship. "We've sent out our agents and most have reported that their policyholders want to know how to better protect themselves."

Washington National Cathedral has been on high alert since Sept. 11.

Capt. Vince Scola, who commands the cathedral's police force, has increased the number of staff per shift. His 17 officers now conduct more physical checks of the building and random checks of backpacks and packages. At special events, they use hand-held metal detectors purchased as a direct result of the assaults on the World Trade Center and Pentagon.

"I hate to admit it, but we can be a potential target just because of what we represent," Scola said. "The National Cathedral is a church for all people. It's a national treasure. We must maintain that thought and be constantly on alert because the best defense is to be on alert."

The cathedral averages between 600 and 800 attendees for weekend services but reaches its 3,200-person capacity during special worship services such as Christmas Eve, Easter and the National Day of Prayer service attended by President Bush and several former presidents on Sept. 14.

Given the potential for terrorist retaliation for the bombing that began Sunday, leaders of nondenominational Southeast Christian Church in Louisville, Ky., said they would continue to re-evaluate security.

"The main threat now is retaliation on the U.S., whether it be a physical or a biological act," said Ron Aguiar, director of safety and security for the church, which draws an estimated 15,000 parishioners to its 100-acre campus each weekend. "If this becomes more and more of a threat, if the FBI raises the bar, then we will do what everybody else does. We will limit accessibility and add even more security."

Sunday night's service, Bible studies and meetings went on as scheduled.

Aguiar's staff patrols the grounds 24 hours a day. In addition, 30 volunteer officers who attend the church assist regularly.

At the Islamic Center of Orange County, Imam Mostafa Qazwii spent some $3,000 on new surveillance cameras and a security system in the week following the terrorist attacks. The Costa Mesa, Calif., center received numerous threatening phone calls from anti-Islamic protesters. Children attending the adjacent City of Knowledge Islamic school have been threatened.

"I never thought twice about it, but now I have to force myself to recognize possible threats at the mosque. I'm a target right away," said Fatma Saleh, who is one of 500 to 1,000 who pray weekly at the Islamic Center and whose three children attend City of Knowledge.

Enrollment at the K-12 school has dropped 30 percent since the attacks because parents fear that their children are not safe.

Qazwii reported hate crimes to local law enforcement officials and has asked their advice on how to better protect the mosque. The center has locked its back entrances indefinitely.

The Islamic Center received no threats on Sunday, Qazwii said, adding that additional patrol cars were sent to the mosque and a handful of members looked for suspicious activity outside the building, as a precaution. Sunday school and an afternoon meeting took place as scheduled.

"We are being more vigilant," Qazwii said. "Osama bin Laden is portraying a war between Islam and Christianity, and it's not. ... We fear that maybe some naive people would believe what he is saying and act accordingly. This is a long campaign and you never know what could happen next."

In Washington, the Basilica of the National Shrine of the Immaculate Conception is the largest church in the Western Hemisphere and eighth-largest in the world. It averages 3,500 parishioners every weekend and over 750,000 visitors annually.

Father Walter Rossi, associate director, termed the measures taken after Sept. 11 "heightened awareness."

On Sunday, the shrine called in additional security guards to protect the evening service and Monday's International Day of Prayer and Fasting, an event that drew 1,000 faithful.

"People were very concerned and anxious," Rossi said Monday. "Our guards were told to be more alert and attentive and look for anything suspicious."

In midtown Manhattan, Central Synagogue, with 4,000 members, is one of the largest temples in the nation. It finished a three-year, $40 million renovation two days before the terrorist attacks.

"We have significantly increased our in-house security since September 11 and reviewed it again yesterday in light of the events," said Livia Thompson, the synagogue's executive director, on Monday. "We have had a 24-hour security presence since the 11th and the number of security guards has doubled, sometimes tripled, depending on if we have a major event."

The synagogue hosted a party Sunday, attended by 2,300 people, without any problems.

"There is a heightened sense of vulnerability," Thompson said. "My sense is that this will go on for a while."

The 8,000 members of the nondenominational Central Christian Church in Henderson, Nev., outside Las Vegas, are used to being watched by law enforcement officials.

"We live in a town where security is a way of life. For every person on the floor (in a casino) there is a security person on the scene," said Mike Bodine, Central Christian's executive director.

Since Sept. 11, Bodine has met with city and security officials to study ways to evacuate the congregation in an emergency. Uniformed and non-uniformed security forces patrol the church grounds and stand guard by the altar during worship services.

"Our security staff is especially trained to watch for any kind of activity that would raise suspicion," Bodine said. "If we saw a threatening situation, we would take action and possibly make arrests.

"Las Vegas is the most secure city in the country. We're trying to make sure the same is true here at Central Christian."

(Jose Alfredo Flores can be contacted at jose.flores@newhouse.com)