Publicly, the White House was standing by Mr. Blair, the United States' top spymaster, who is responsible for coordinating intelligence gathering among 16 agencies, saying the four-star admiral had the full confidence of the president.
"This is not about one person or one agency," White House press secretary Robert Gibbs said.
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Also Wednesday, it was revealed that a similar effort, starting in Somalia, to down a jetliner was thwarted at an earlier stage, and a pilots union complained that its members were not immediately told of the attack on Northwest Flight 253 - a practice the union said must change.
But Washington speculation was rife that Mr. Blair or Homeland Security Secretary Janet Napolitano could be forced to resign after President Obama said Tuesday there had been a systemic failure by the country's security agencies to prevent the botched Christmas Day attack.
Ms. Napolitano has been lambasted by Republican critics, and in the media, for initially saying the air-security system worked, and then backpedaling and saying she had meant the system of beefing up measures worked after the incident had occurred.
A senior aide said Mr. Obama would seek accountability at the highest levels for the failure, a remark some observers took to mean that heads would roll.
Mr. Obama is under pressure from Republicans, who fault his administration for not preventing the attack and the president for keeping silent about it for three days while on vacation in Hawaii.
The Republicans portrayed Mr. Obama as weak on national security even as he campaigned for last year's presidential election, and have sought to push that point before midterm elections in November, when they will challenge the Democrats' control of both houses of Congress.
"The terrorist plot to bring down Northwest Airlines Flight 253 exposed a near-catastrophic failure at every level of our government," said House Minority Leader John A. Boehner, Ohio Republican.
Former Vice President Dick Cheney, who staked out a position as a leading security hawk under President George W. Bush after the Sept. 11, 2001, attacks and is a vocal critic of Mr. Obama's national security policies, also weighed in.
He told Politico: "As I've watched the events of the last few days, it is clear once again that President Obama is trying to pretend we are not at war."
"He seems to think if he has a low-key response to an attempt to blow up an airliner and kill hundreds of people, we won't be at war."
White House Communications Director Dan Pfeiffer retorted that it was "telling that Vice President Cheney and others seem to be more focused on criticizing the administration than condemning the attackers."
"Unfortunately, too many are engaged in the typical Washington game of pointing fingers and making political hay, instead of working together to find solutions to make our country safer," Mr. Pfeiffer said in a blog post on WhiteHouse.gov.
Umar Farouk Abdulmutallab, a 23-year-old Nigerian, is charged with smuggling explosives on board and attempting to blow up the Northwest Airlines flight as it approached Detroit from Amsterdam with almost 300 people on board.
U.S. officials said Wednesday that they are also investigating a Somali man's purported attempt to board a flight bound for Djibouti and Dubai last month carrying chemicals, liquid and a syringe in a case bearing chilling echoes of the Detroit plot.
Terrorism analysts said the arrest in Mogadishu, the Somali capital, could prove highly valuable for the Detroit investigation if the incidents turn out to be linked.
The Somali was arrested by African Union peacekeeping troops Nov. 13 before boarding the Daallo Airlines plane bound for the northern Somali city of Hargeisa, then Djibouti and Dubai.
"We don't know whether he's linked with al Qaeda or other foreign organizations, but his actions were the acts of a terrorist. We caught him red-handed," said a Somali police spokesman, Abdulahi Hassan Barise.
In candid criticism of the failures that could have led to disaster, Mr. Obama said U.S. security agencies had failed to piece together bits of information to prevent Mr. Abdulmutallab from boarding the flight with explosives.
As director of national intelligence, it is Mr. Blair's job to connect the dots. The position was created by Congress in an effort to correct the intelligence failures blamed in part for the Sept. 11, 2001, hijacked-plane attacks on the United States.
Mr. Obama has ordered a review of information sharing procedures and he is due to receive a preliminary report Thursday. Mr. Gibbs said he was uncertain whether the findings would be made public.
The pilots complaint came from the union at American Airlines, which said Wednesday it would lobby Congress to require that federal officials notify all flights in the air - no matter where the flights started - as soon as they learn of a possible attack on another plane.
Federal officials said they limited immediate notification of the Dec. 25 bombing attempt to crews on U.S.-bound flights from Europe because they were considered to face the greatest danger.
"Based on intelligence information at that time, a strategic, risk-based decision was made to notify all 128 flights inbound from Europe," said Transportation Security Administration spokeswoman Sterling Payne.
But Mike Karn, an American pilot and the union's security chairman, questioned how such a determination of what planes were at risk could have been made at the time. "They hadn't determined at that point if this was a sole actor or part of a broader plot," he said.