Washington ? The Bush administration’s long-held assertion that it lacked the evidence to avert the terror attacks is giving way to a crucial question: What did the government know before Sept. 11?

The administration’s theme has been that it had no specific information and therefore could not stop the plotters.

FBI Director Robert Mueller set the tone Sept. 14, saying the attacks might have been thwarted had investigators understood the terrorists got their pilot training at U.S. flight schools.

“Is there a piece of information out there … that nobody saw? That’s not the case,” CIA Director George Tenet told the Senate Intelligence Committee in February, in response to a question by one of Tenet’s harshest critics, Sen. Richard Shelby, R-Ala.

The statements by Mueller, Tenet and others stood unchallenged until last month, when the pre-Sept. 11 secrets of the FBI and the CIA started spilling out amid congressional inquiries.

It began coming together in public last week as the Senate Judiciary Committee questioned Mueller at a hearing. Separately, the House and Senate intelligence committees started their joint hearings, which are closed now but go public June 25.

The secrets:

l The Phoenix memo, an FBI agent’s warning two months before the attacks that U.S. flight schools might be training terrorist pilots.

l FBI whistle-blower Coleen Rowley’s letter pointing to what she says was solid information from French intelligence that justified an aggressive probe of Zacaraias Moussaoui weeks before Sept. 11. FBI headquarters blocked its own agents from seeking a search warrant for the laptop computer and belongings of Moussaoui, who now faces trial for conspiracy in the attacks.

l Detailed intelligence in the CIA’s files on two of the hijackers. The spy agency, which shared some of what it had with the FBI, failed to act on the information until it was too late.

l Before hijacked planes hit the Pentagon and World Trade Center, the National Security Agency apparently recorded an Arabic-language telephone conversation that referred to a big event planned for Sept. 11. It appears the conversation was not translated until after the attacks.

The secrets constitute a lesson for an administration that made categorical statements early on.

After Mueller’s Sept. 14 comment at a news conference, subordinates cautioned the boss not to repeat it. They had known about the Phoenix memo. Mueller had not. He had been on the job only a week.

“I lived through every scandal from Watergate on, and the overriding lesson is the importance of never making a declarative statement that you have found all the information,” said former CIA Director Robert Gates.

In the aftermath of Sept. 11, however, “the tragedy was so huge people were looking for declarative statements and assurances that were hard to avoid,” said Gates.

Most veteran Washington observers believe there will be more pre-Sept. 11 disclosures.

“I am sort of agnostic at this point as to whether we knew enough to stop” Sept. 11, said L. Paul Bremer, former ambassador at large for counterterrorism during the Reagan administration.

But “as they go through this in the intelligence committees, you’re probably going to come up with other data points” like the Phoenix memo and information in the CIA’s files on the two hijackers, said Bremer.

“Then the question is, ‘Is there anybody who had access to all of these data points so that he could have had a broader picture and taken steps that actually would have made a difference?”‘ asked the former ambassador, who now heads a crisis consulting firm.