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Mr. Rangel, former chairman of the tax-writing House Ways and Means Committee, is charged with financial and fundraising misconduct, and has acknowledged some ethical lapses.

Mrs. Waters, a senior member of the Financial Services Committee, is contesting charges that she sought federal aid for a bank where her husband is an investor.

Republicans on the House ethics committee demanded Tuesday that trials for the two lawmakers be completed before the November elections.

Melanie Sloan, director of Citizens for Responsibility and Ethics in Washington and a former Democratic congressional aide, credits Mrs. Pelosi with bringing about much of the culture change she promised.

She cited the end of the Republican “K Street Project,” used by former GOP leader Rep. Tom DeLay of Texas to pressure lobbying firms to hire Republicans who then were given access to top officials.

But many Republicans are dismissive of the majority’s efforts and vow their own reforms should they take power next year.

GOP Rep. Dan Lungren, the former attorney general of California, said many of the ethics improvements Mrs. Pelosi takes credit for were the result of bipartisan agreements on the 2007 law signed by Mr. Bush. Republicans were first with the idea of identifying sponsors of special-interest spending, he said.