WASHINGTON, April 9— President Bush was told more than a month before the attacks of Sept. 11, 2001, that supporters of Osama bin Laden planned an attack within the United States with explosives and wanted to hijack airplanes, a government official said Friday.
The warning came in a secret briefing that Mr. Bush received at his ranch in Crawford, Tex., on Aug. 6, 2001. A report by a joint Congressional committee last year alluded to a ''closely held intelligence report'' that month about the threat of an attack by Al Qaeda, and the official confirmed an account by The Associated Press on Friday saying that the report was in fact part of the president's briefing in Crawford.
The disclosure appears to contradict the White House's repeated assertions that the briefing the president received about the Qaeda threat was ''historical'' in nature and that the White House had little reason to suspect a Qaeda attack within American borders.
Members of the independent commission investigating the Sept. 11 attacks have asked the White House to make the Aug. 6 briefing memorandum public. The A.P. account of it was attributed to ''several people who have seen the memo.'' The White House has said that nothing in it pointed specifically to the kind of attacks that actually took place a month later.
The Congressional report last year, citing efforts by Al Qaeda operatives beginning in 1997 to attack American soil, said that operatives appeared to have a support structure in the United States and that intelligence officials had ''uncorroborated information'' that Mr. bin Laden ''wanted to hijack airplanes'' to gain the release of imprisoned extremists. It also said that intelligence officials received information in May 2001, three months earlier, that indicated ''a group of bin Laden supporters was planning attacks in the United States with explosives.''
Also on Friday, the White House offered evidence that the Federal Bureau of Investigation received instructions more than two months before the Sept. 11 attacks to increase its scrutiny of terrorist suspects inside the United States. But it is unclear what action, if any, the bureau took in response.
The disclosure appeared to signal an effort by the White House to distance itself from the F.B.I. in the debate over whether the Bush administration did enough in the summer of 2001 to deter a possible terrorist attack in the United States in the face of increased warnings.
A classified memorandum, sent around July 4, 2001, to Condoleezza Rice, the president's national security adviser, from the counterterrorism group run by Richard A. Clarke, described a series of steps it said the White House had taken to put the nation on heightened terrorist alert. Among the steps, the memorandum said, ''all 56 F.B.I. field offices were also tasked in late June to go to increased surveillance and contact with informants related to known or suspected terrorists in the United States.''
Parts of the White House memorandum were provided to The New York Times on Friday by a White House official seeking to bolster the public account provided a day before by Ms. Rice, who portrayed an administration aggressively working to deter a domestic terror attack.
But law enforcement officials said Friday that they believed that Ms. Rice's testimony before the commission investigating the Sept. 11 attacks -- including her account of scores of F.B.I. investigations under way that summer into suspected Qaeda cells operating in the United States -- overstated the scope, thrust and intensity of activities by the F.B.I. within American borders.
Agents at that time were focused mainly on the threat of overseas attacks, law enforcement officials said. The F.B.I. was investigating numerous cases that involved international terrorism and may have had tangential connections to Al Qaeda, but one official said that despite Ms. Rice's account, the investigations were focused more overseas and ''were not sleeper cell investigations.''
The finger-pointing will probably increase next week when numerous current and former senior law enforcement officials, including Attorney General John Ashcroft, testify before the Sept. 11 commission. In an unusual pre-emptive strike, Mr. Ashcroft's chief spokesman on Friday accused some Democrats on the commission of having ''political axes to grind'' in attacking the attorney general, who oversees the F.B.I., and unfairly blaming him for law enforcement failures.
A similar accusation against the commission was also leveled by Senator Mitch McConnell, a Kentucky Republican with ties to the White House, in a speech on the Senate floor Thursday.
''Sadly, the commission's public hearings have allowed those with political axes to grind, like Richard Clarke, to play shamelessly to the partisan gallery of liberal special interests seeking to bring down the president,'' Mr. McConnell said.
The charges and countercharges underscored the political challenge that the investigation into the Sept. 11 attacks has become for President Bush as he mounts his re-election bid. The White House sought this week to defuse the situation by allowing Ms. Rice to testify before the Sept. 11 commission after months of resistance. But her appearance served to raise new questions about the administration's efforts to deter an attack.
