But her assertions did not deflect harsh questions or criticisms about the federal response from the Democrats in the room.  “Our government has knowingly exposed thousands of American citizens unnecessarily to deadly hazardous materials,” said Representative Jerrold Nadler, the chairman of the subcommittee and a Manhattan Democrat whose district includes ground zero. “And because it has never admitted the truth, Americans remain at grave risk to this day.”  Mrs. Whitman initially refused to testify before the subcommittee because she said she was not qualified to discuss legal issues. After checking with her lawyers, she agreed to appear. She also is named in at least three pending lawsuits brought against the agency by city residents and workers.  The hearing carried a political overtone because the lingering health issues have raised questions about Mayor Rudolph W. Giuliani’s handling of worker safety at ground zero, now that he is a candidate for the Republican nomination for president. But at the hearing Mrs. Whitman, the former Republican governor of New Jersey, did not direct blame at the Giuliani administration for the failure to require that all workers at the site wear respirators.  “I don’t think the mayor is blaming me and I’m certainly not blaming the mayor,” Mrs. Whitman said during two and a half hours of questioning that at times turned testy, particularly when members of the panel pressed her on seeming contradictions in statements she made five and a half years ago.  Several members of the committee repeatedly quoted from a comprehensive 2003 report by the E.P.A.’s own inspector general that concluded that Mrs. Whitman did not have sufficient scientific information to warrant stating, on Sept. 18, 2001, that the air in New York was “safe to breathe.” The report also detailed how the White House had altered her press releases.  Mrs. Whitman said she was aware of only one instance in which important information was removed from one of her public statements by the President’s Council on Environmental Quality, which edited the statements in the aftermath of the attack. In one draft release in September, Mrs. Whitman urged Lower Manhattan residents whose apartments had been contaminated to consider having them professionally cleaned. After the statement was sent to the White House for review, the phrase about professional cleaning was removed.  Mr. Whitman said that early on a decision had been made by the Bush administration that all public statements be coordinated so that the federal government could be seen as speaking with one voice, an assertion that drew an angry response from Representative Bill Pascrell, a New Jersey Democrat.  “One voice — give me a break,” Mr. Pascrell said.  Several members of the subcommittee also pressed Mrs. Whitman to acknowledge that exposure to the dust from the collapsed twin towers had made workers and residents sick. Mrs. Whitman declined to do so, saying that the evidence linking the dust to disease was not conclusive.  She said she had not read clinical reports from the Mount Sinai World Trade Center Screening and Monitoring Program. A preliminary study released last year showed that 70 percent of the first 9,000 workers examined had reported developing some kind of respiratory problem after working on the debris pile.  At one point in the questioning, Representative Keith Ellison, Democrat of Minnesota, expressed disbelief about statements that Mrs. Whitman made in 2001 because they seemed to contradict the results of air sampling being reported by the agency’s own scientists.  When Mrs. Whitman, in response to his questioning, mentioned that she had feared for the life of her own son, who worked at 7 World Trade Center, Mr. Ellison refused to allow her to express her personal concerns.  “I’m not going to stand here and allow you to try to obfuscate,” he said.  Mrs. Whitman then raised her voice. “I’m not obfuscating,” she said. “I have been called a liar even in this room today.”  Mrs. Whitman denied claims by committee members that she had been pressured to declare the air safe so the financial district could be reopened quickly, and she did not express regret for any of her statements in 2001. She acknowledged that there were early discussions at a high level about evoking the federal Superfund law, which would have given the E.P.A. broad powers to control the site. Although that option was considered, it was quickly ruled out for legal and political reasons, she said.  “We were working in a collegial nature with New York City,” she said. She said she had feared that New Yorkers would react badly if the federal government took the city to court to make the case that the debris pile represented “a substantive and imminent danger,” a finding that would give the federal government the right to seize control of the site.  John L. Henshaw, a former assistant secretary of labor who led the Occupational Safety and Health Administration in 2001, defended the controversial decision by the federal agency to not strictly enforce regulations on the use of respirators by workers at ground zero.  Instead, the agency entered into a partnership with the large construction companies working at the site, and the city, to voluntarily comply with the regulations. The city’s own records, however, indicate that compliance was often spotty.  A version of this article appears in print on , on Page B1 of the New York edition with the headline: Whitman Defends Air Quality Assurances Made After 9/11. Order Reprints| Today's Paper|Subscribe
In a hearing with political overtones, Christie Whitman said that charges that she or other E.P.A. officials misled the public were “utterly false.”