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Republican Rep. Bill Thomas, the powerful chairman of the House Ways and Means Committee, announced Monday he will retire from Congress after serving for more than a quarter century.

Thomas, 64, made the announcement in his hometown of Bakersfield.

His resignation was widely expected because, under House Republicans' self-imposed term limits for committee chairmen, Thomas can no longer serve after this year as head of the influential Ways and Means Committee.

"Today I am announcing that I will not seek reelection to the United States Congress," he said.

For the past five years, Thomas has played a key role in shepherding Bush's tax cuts and writing legislation on Medicare, Social Security and pensions.

His knowledge of such complicated issues made him indispensable to party leaders, despite complaints that he was difficult to work with and not conservative enough because of some votes for abortion rights and gun control.

Some colleagues believe Thomas rescued Bush's tax cut proposal in 2003 after the Senate refused to go along with its initial cost. He was instrumental in securing congressional passage of Bush's Medicare prescription drug bill and of "fast track" trade promotion authority.

At the same time, his clashes with other lawmakers, usually Democrats, became famous on Capitol Hill. He called out the Capitol police three years ago to break up a meeting of Democrats on his committee, then expressed regret in tears on the House floor.

In the tussle over the trade bill, he labeled as "dumb and outlandish" questions from Rep. Alcee Hastings, D-Fla. He had to apologize to Sen. Dianne Feinstein, D-Calif., after accusing her of lacking guts on the medical malpractice issue and wrongly attributing her position to the fact that the senator was facing reelection, which she was not.

Thomas taught American government at Bakersfield Community College before joining Congress in 1979. The annual financial disclosure forms lawmakers file each year showed him to be among the most modest-meaned members of Congress — he regularly listed no assets or income beyond his congressional salary, now $165,200.

His 22nd Congressional District, at the southern end of California's agriculture-rich Central Valley, is expected to stay firmly in GOP control. Republicans make up 52 percent of registered voters in the district, compared to 30 percent for Democrats.