ASHINGTON, May 30 — With admissions this week that the F.B.I. might have been able to foil the Sept. 11 attacks and that it had bungled additional clues, Robert S. Mueller III has contradicted much of his past public defense of the bureau, raising new concern today on Capitol Hill about his leadership of the embattled agency.
Lawmakers said in interviews that the F.B.I. director was secure in his job for now and that they welcomed the plans he announced on Wednesday to change and enlarge the bureau's counterterrorism program.
But they said a review of his public remarks about the Sept. 11 investigation had raised uncomfortable questions about the F.B.I. director's credibility and about his ability to gather accurate information from his deputies.
Mr. Mueller's credibility was harshly attacked in a letter made public last weekend in which a Minneapolis agent said the F.B.I. director was engaged in a public relations campaign "to protect the F.B.I. at all costs" after Sept. 11.
In a news conference on Wednesday that amounted to a painful mea culpa for the bureau and for his performance in the nine months since he took over the Federal Bureau of Investigation, Mr. Mueller said, "I have made mistakes occasionally in my public comments based on information or a lack of information that I subsequently got."
He was referring specifically to a widely publicized Sept. 14 statement in which he offered assurances — later proved to be false — that the bureau had no warning that terrorists might be training in American flight schools. On Sept. 17, Mr. Mueller went further, saying he knew of "no warning signs" of any sort of attack.
Senator Charles E. Grassley, an Iowa Republican who is on the Judiciary Committee, said his staff investigators would explore the accusations made by the Minneapolis agent, Coleen Rowley, that Mr. Mueller and other senior F.B.I. officials had intentionally shaded the truth about the investigation last summer of Zacarias Moussaoui.
Mr. Moussaoui, who has been charged with conspiring in the Sept. 11 attacks, was arrested in Minnesota in August. Ms. Rowley said F.B.I. headquarters had obstructed the work of the local office in determining if Mr. Moussaoui was a terrorist.
"I believe that his heart is in the right spot," Senator Grassley said of Mr. Mueller, a decorated Vietnam War veteran and career federal prosecutor who until this week had received almost universal praise on Capitol Hill for his early performance at the F.B.I.
"But I'm going to give a great deal of deference to a whistle-blower," Mr. Grassley said of Ms. Rowley. "It gives me responsibility for digging deeper."
Mr. Grassley said that senior aides to Mr. Mueller may be to blame for the misstatements that had come back to haunt the F.B.I. director and that Mr. Mueller's deputies should be held accountable if they were responsible. "I'm willing to forgive him," the senator said. "But I'm not willing to forgive the agents who gave him the information."
Senator Dianne Feinstein, a California Democrat who is a member of the Judiciary and Intelligence committees, said she was perplexed by some of the inaccuracies that have been uncovered in Mr. Mueller's public statements, and that she was concerned that they might reflect an unwise decision to "take on the burden of defending what has been done in the past."
But she said that inadvertent mistakes by Mr. Mueller in his public comments might be understandable, especially in his first few, chaotic weeks on the job. "I have no concerns that he is up to the task," she said. "I think he has to be given a fair chance to prove himself."
A review of Mr. Mueller's public remarks since Sept. 11 shows that the director, who arrived at the F.B.I. only a week before the attacks, was quick to defend the bureau's performance and to suggest that there was little the F.B.I. could have done to prevent the attacks.
Some of his early remarks have proved to be untrue, and he has made what appear to inconsistent statements on other elements of the inquiry, notably the Moussaoui case.
"The tragedies quite clearly astonish and shock me and the country," he said at a news conference on Sept. 14. "The fact that there were a number of individuals that happened to have received training at flight schools here is news, quite obviously. If we had understood that to be the case, we would have — perhaps one could have averted this."
Three days later, in the wake of news reports about Mr. Moussaoui's arrest, Mr. Mueller was asked again if the bureau had missed "any warning signs." He offered a more wide-ranging defense, saying, "There were no warning signs that I'm aware of that would indicate this type of operation in the country."
In her May 21 letter to the F.B.I. director, Ms. Rowley said she and other Minneapolis agents had been alarmed by Mr. Mueller's public comments and "immediately sought to reach your office through an assortment of higher-level F.B.I.-HQ contacts, in order to quickly make you aware of the background of the Moussaoui investigation and forewarn you so that your public statements could be accordingly modified."
But she said that when Mr. Mueller and his deputies repeated the comments in the weeks that followed, the Minneapolis agents "faced the sad realization that the remarks indicated someone, possibly with your approval, had decided to circle the wagons at F.B.I. HQ in an apparent effort to protect the F.B.I. from embarrassment."
Questioned this week about Ms. Rowley's accusations, Mr. Mueller conceded that his Sept. 14 statement had been in error and that he had been unaware that day of a memorandum sent to F.B.I. headquarters in July by a Phoenix agent who had called for a nationwide investigation of flight schools in light of evidence suggesting that Arab men with ties to terrorist groups might be seeking training.
"The fact of the matter is when I made that statement, I wasn't aware of the Arizona E.C.," Mr. Mueller said Wednesday, using the initials for electronic communication. "After I made that statement at the press conference, somebody brought it to my attention that, look there's this Phoenix E.C. out there."
The review of his public comments shows that Mr. Mueller has also given other seemingly contradictory statements about the Moussaoui case — specifically, about why the bureau did not pursue a warrant before Sept. 11 that might have allowed Minneapolis agents to search his computer, where evidence linking him to the hijackers was found.
In October and again in December, when he announced Mr. Moussaoui's indictment, Mr. Mueller said publicly that there had been insufficient evidence before Sept. 11 to request the court order sought by the Minneapolis agents.
"When it was looked at, there was insufficient probable cause — clear, insufficient probable cause," Mr. Mueller explained in October. In December, he said again that "attorneys back at F.B.I. determined that there was insufficient probable cause," which "appears to be an accurate decision."
But on Wednesday, Mr. Mueller backed away from his earlier statements, saying that he had not made a decision on whether the search warrant should have been sought. "I haven't parsed it," he said. "I know the Hill is looking at that."