Washington ? President Bush expressed doubt Tuesday that the leaker who exposed a covert spy’s identity would ever be found, saying the capital “is a town full of people who like to leak information” and few are ever caught.

As 2,000 White House employees worked to meet a late afternoon deadline Tuesday for documents requested by Justice Department investigators probing the leak, the White House said it would screen the material for relevance before giving it to prosecutors.

That drew a rebuke from one of the administration’s sharpest critics on this issue, Sen. Charles Schumer, D-N.Y.

And White House spokesman Scott McClellan did not rule out the possibility that the White House might decline to turn over material for other reasons, such as executive privilege or national security, saying it was premature to discuss those issues.

McClellan also expanded a formal denial of involvement to include two more officials: Lewis Libby, chief of staff to Vice President Dick Cheney, and National Security Council aide Elliott Abrams. McClellan had previously issued a denial on behalf of chief political strategist Karl Rove. But McClellan once again drew a distinction between leaking classified information — which he said Rove, Libby and Abrams were “not involved in … nor would they condone” — and what McClellan termed “setting the record straight” about former U.S. diplomat Joseph Wilson and his controversial trip to Africa.

The CIA sent Wilson to Niger early last year to check out allegations that Iraq was trying to buy enriched uranium. Wilson reported back that the charge was baseless; Bush nonetheless repeated it in his State of the Union speech.

In July, just after Wilson publicly disclosed his mission and accused Bush of distorting the facts on Iraq, columnist Robert Novak reported that Wilson’s wife, Valerie Plame, was a CIA operative. Novak cited “two senior administration officials” as sources. Newsday later revealed that Plame was undercover.

For the second day in a row, McClellan answered questions about Rove’s possible involvement in steering other journalists to Novak’s column by saying that “there is a difference between setting the record straight and people going out trying to punish someone for speaking out.” The White House, McClellan said, had been anxious to have it known that the CIA, not Cheney’s office, had sent Wilson to Niger.

Bush, speaking with reporters at the White House, repeated his desire to “know the truth” about the identity of Novak’s source but voiced skepticism that it would emerge, in part because the news media protects leakers. “How many sources have you had (who’ve) leaked information that you’ve exposed or have been exposed? Probably none,” he said. “This is a town full of people who like to leak information. And I don’t know if we’re going to find out the senior administration official. Now, this is a large administration, and there’s a lot of senior officials.”

As the 5 p.m. deadline for submitting all relevant documents to the counsel’s office neared, Chief of Staff Andrew Card sent a memo to employees reminding them of the need to meet it. McClellan said the counsel’s office would review submissions to determine if they were relevant, saying that was necessary because some staffers might be “erring on the side of providing more than they should.”

But Schumer said it was not clear what standards would be used to determine relevancy. “Let Justice determine that,” he said. “Ask any prosecutor worth his salt. They don’t want people with a possible relationship to the guilty person making those determinations. It should be the prosecutors themselves.”