The government's very public warning to financial institutions may actually deter a bombing but also raises questions about what the next step will be for both terrorists and defenders.

And among security experts and former counterintelligence officials who had criticized previous terrorism warnings as too vague or perhaps politically motivated, there was wide praise for the unique level of detail in the warning Sunday to a handful of specific financial institutions in New York, Washington and Newark, N.J.

"If I worked in one of those buildings, I would feel very safe now," and not just because the security there will be tightened, said Vince Cannistraro, former CIA (search) counterterrorism chief. "Given that it's captured material and now made public, there's a good chance it won't happen. Al Qaeda has to realize the mission has been compromised."

Among the extraordinary detail that Al Qaeda (search) operatives had assembled about potential target buildings were such details as architectural elements that might prevent collapse, a count of 14 pedestrians per minute along the sidewalk outside one building at midweek, locations of security checkpoints inside buildings and identification of days when fewer guards worked or elevators were shut down, a senior intelligence official said.

The government's willingness to cite specific buildings as targets "is a step forward, compared to the past when they just waved a red flag and said 'Al Qaeda's coming, Al Qaeda's coming,'" said I.C. Smith, a retired FBI (search) field office chief who spent most of his 25-year career in counterintelligence.

"You are going to end up with some awfully nervous people who work in and around those buildings," Smith said.

But if captured information isn't part of an outdated plot, the warning could abort a planned truck bombing, Smith said. A counterterrorism official, requesting anonymity because of the sensitivity, said the Al Qaeda operatives conducted the vulnerability assessments in the captured material both before and after the Sept. 11, 2001, attacks.

Smith added, however, that authorities need to be alert to the chance Al Qaeda might be trying to deceive U.S. agents. "Someday they are going to send us indications they are going one way and then go another way. That will happen sooner or later," Smith said.

John Pike, a defense analyst with GlobalSecurity.org, said Sunday's alert "was outstanding compared to previous ones. At least I know which buildings to stay away from."

But the proximity of the target buildings to the street raised other questions in Pike's mind. Would Pennsylvania Avenue be closed to truck traffic outside the World Bank? Local officials planned additional vehicle checks but did not immediately close any streets.

"And all the enemy has to do is dial down its list of prominent targets," Pike added. "If they can't reach the World Bank, maybe they'll go for the Federal Reserve or the FBI," both of which are only handful of blocks away in either direction.

At some point, "if you going to try to defend all the high-value targets in Washington from truck bombs, you might turn the entire federal core into a pedestrian mall."