President Obama vowed yesterday to use "every element of our national power" to keep Americans safe and said the failed Christmas Day attempt to blow up a Detroit-bound jet was "a serious reminder" of the need to continually adapt security measures against changing terrorist threats.

As he spoke, word came that a State Department warning had failed to trigger an effort to revoke the U.S. tourist visa held by the alleged attacker, Umar Farouk Abdulmutallab.

Friday's incident aboard a Northwest Airlines jet prompted stiffer airport boarding measures, and authorities warned holiday travelers to expect extra delays as they return home this week and beyond. But some airline officials said the in-flight restrictions imposed during the weekend had been eased.

The Transportation Security Administration did little to explain the rules, though the inconsistency might have been deliberate: What's confusing to passengers is also confusing to potential terrorists.

Spokeswoman Sterling Payne said only that the TSA would "continually review and update these measures to ensure the highest level of security."

Abdulmutallab, 23, is accused of trying to detonate an explosive device hidden on his body as Northwest Flight 253, an Airbus A330-300 carrying 290 people, approached Detroit.

He is being held at the federal prison in Milan, Mich., charged with trying to destroy an aircraft. A hearing to determine whether the government can obtain DNA from him was postponed until Jan. 8 without explanation.

Calling Abdulmutallab's action an "attempted act of terrorism," Obama, who is on vacation in Hawaii, declared: "The United States will more than simply strengthen our defenses. We will continue to use every element of our national power to disrupt, to dismantle and defeat the violent extremists who threaten us."

He detailed two reviews he has ordered to determine whether changes are needed in either the watch-list system or airport screening procedures.

"It's absolutely critical that we learn from this incident," he said.

Members of Congress questioned how a man flagged as a possible terrorist managed to board a U.S.-bound flight carrying powerful explosives and nearly bring down the jet. Sen. Joe Lieberman (I., Conn.) said the Homeland Security and Governmental Affairs Committee he chairs would hold hearings in January.

Federal officials met to review their layered system of watch lists and other procedures to examine how to prevent the type of lapses that led to the attack.

Two federal sources briefed on the investigation told the Washington Post that the PETN explosive allegedly concealed by Abdulmutallab could have blown a hole in the jet's side had it been detonated.

Abdulmutallab's family in Nigeria said his father, prominent banker Alhaji Umar Mutallab, reached out to Nigerian security agencies two months ago, then approached foreign security agencies for "their assistance to find and return him home."

U.S. officials say that is how Abdulmutallab came to the attention of American intelligence last month, when the father reported his concerns to the U.S. Embassy in Abuja that his son "had fallen under the influence of religious extremists."

These concerns landed Abdulmutallab among the 550,000 names in the Terrorist Identities Datamart Environment database, which the National Counterterrorism Center maintains. Smaller lists trigger additional airport screening or other restrictions, but intelligence officials said there had not been enough information to move him into those categories.

Britain, where Abdulmutallab graduated last year from a London university, refused in May to grant him a subsequent student visa, saying the school on his application form was not a government-approved institution. Home Secretary Alan Johnson said U.S. authorities should have been informed that Abdulmutallab had been placed on the British list and believed that all procedures had been followed correctly.

But there was no apparent effort to revoke his U.S. visa, issued in June 2008 and good for multiple entries over two years. He also visited in 2004 on an earlier visa.

The embassy visit by Abdulmutallab's father triggered a Nov. 20 State Department cable from Nigeria to all U.S. diplomatic missions and Washington headquarters. State Department spokesman Ian Kelly said the National Counteterrorism Center found the information "insufficient to determine whether his visa should be revoked."

Michael Chertoff, homeland security secretary in the Bush administration, said it was a "serious indicator" when a parent went to authorities to discuss concerns about his child, and it "certainly would cause me to ask questions."

Homeland Security Secretary Janet Napolitano conceded yesterday that the aviation-security system had failed, backtracking from a statement Sunday in which she said it had worked.

After the weekend security clampdown, the TSA relaxed rules that had barred passengers from leaving their seats, opening carry-ons, and keeping blankets on their laps in the last hour of U.S.-bound international flights, said an official who spoke on condition of anonymity because the TSA had not publicly disclosed the change.

Crews were authorized to impose restrictions for shorter periods or not at all, the official said.

On some flights yesterday, passengers were told to keep their hands visible and not to listen to iPods. But on other planes, security appeared no tighter than usual.

Airlines had objected to a TSA order to shut off in-flight entertainment systems on international flights. The TSA apparently relented Sunday night and left the decision to airline crews' discretion.

Canadian officials yesterday banned most carry-ons for U.S.-bound passengers, allowing only medical devices, small purses, cameras, laptops, canes, walkers, diaper bags, and musical instruments.

What's What With Watch Lists

U.S. officials are reviewing their watch-list and screening procedures, but not all lists are equal. Here is a look at them:

Terrorist Identities Datamart Environment database: This is the largest collection, with about 550,000 people. U.S. intelligence, law enforcement, and trusted allies can nominate "known or suspected terrorists" for the database, which is maintained by the National Counterterrorism Center and was set up in the wake of 9/11. Umar Farouk Abdulmutallab was in this database.

Consolidated Terrorist Watch List: About 400,000 names. People are moved onto this list, which is maintained by the FBI's Terrorist Screening Center, after two requirements are met. First, there must be sufficient biographical and identifying data so that the person being screened can be matched to the name, and second, there must be enough information to justify a "reasonable suspicion" that the person is known or suspected to be engaged or preparing to engage in terrorist activities.

Selectee List: A subset of the watch list, with about 14,000 people. People are placed on this list when there is more information about their suspected terrorist activities that suggests they may pose a threat, including to aviation. These people require more stringent, or "secondary," screening when they fly.

No-fly List: Also a subset of the watch list, with about 3,400 people, including roughly 170 U.S. residents. To be put on the no-fly list, a known or terror suspect must meet more specific criteria showing he or she is a threat to civil aviation or national security.

SOURCE: Associated PressEndText