Rep. Henry A. Waxman (D-Beverly Hills) announced Thursday that he would not seek a 21st term in the U.S. House. In a statement, Waxman, 74, said it was simply his time to go.

WASHINGTON — Rep. Henry A. Waxman, whose legislative record has made him one of the country’s most influential liberal lawmakers for four decades, announced Thursday that he will retire from his Westside seat, the latest in a wave of departures that is remaking the state’s long-stable congressional delegation.

During a congressional career that began when Gerald R. Ford was president, Waxman became one of the Democratic Party’s most prolific and savvy legislators, focusing on issues related to healthcare and the environment. He played a central role — sometimes over opposition within his own party — in passing laws that dramatically cut air pollution, helped reduce smoking, expanded Medicaid coverage for the poor, reduced pesticides in food, made generic drugs more widely available, helped AIDS patients, promoted the development of drugs for rare diseases and improved federal regulation of nursing homes.

Among his legislative victories was the 2010 Affordable Care Act, which he helped write and push through the House. Passage of the law fulfilled “one of my lifelong dreams” by guaranteeing access to healthcare coverage for Americans, he said.

Often assailed by Republicans for his partisanship, Waxman has been equally lauded by Democrats for his skill at finding legislative compromises that have pushed a host of landmark bills into law. Bald, mustachioed and 5-foot-5, he is also known as a tough political infighter who has not hesitated to push aside rivals who stood in the way of what he considered important goals. The walls of his Capitol Hill office are covered with framed copies of bills he authored and pens used by Democratic and Republican presidents to sign into law numerous measures, any one of which might have been considered a capstone by other lawmakers.

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During the George W. Bush administration, Waxman established a reputation as an investigatory pit pull, staging high-profile hearings that drew headlines as well as protests from administration officials.

His California colleague, Rep. George Miller (D-Martinez), who announced his own retirement earlier this month, once quipped to a Washington political journal that he thought Waxman’s first name was "sonuvabitch, because everyone ... kept asking, 'Do you know what that sonuvabitch Waxman wants now?' "

His highest-profile hearing came in 1994, when he summoned the heads of the nation’s tobacco companies to a televised session on the dangers of smoking. The public testimony by the chief executives, in which they claimed not to believe cigarettes were addictive, became a "turning point in our national history," Waxman later wrote in a book with Joshua Green, “The Waxman Report: How Congress Really Works.”

Fifteen years later, President Obama, who has had his own struggles to quit smoking, cited the hearing in signing legislation cosponsored by Waxman that gave the federal government new authority to regulate tobacco.

Waxman’s retirement likely will set off a scramble of politicians seeking to represent his heavily Democratic 33rd District. In addition to being a relatively safe seat, its many wealthy, politically active residents make the district, which runs from Beverly Hills and Malibu down the coast to the Palos Verdes Peninsula, one of country’s leading sources of campaign contributions. The ability to steer those donations to fellow lawmakers offers a path to power in the House that Waxman employed actively early in his career and that others will certainly covet.

Two political independents already had announced plans to challenge Waxman this year, but Democratic candidates who would not have run against the incumbent are now likely to enter the race.

In an interview, Waxman, 74, said he had decided, simply, that the time had come to do something else.

“At the end of this year, I would have been in Congress for 40 years,” he said. “If there is a time for me to move on to another chapter in my life, I think this is the time to do it.

“I have run my last campaign,” he said.

Waxman’s departure will significantly weaken California’s clout on Capitol Hill, where seniority still matters. He is the House's sixth-most senior member and the fourth veteran California congressman to head for the exits this year. Along with Miller he was the last of the huge class of Democrats elected in the post-Watergate election of 1974 who are still serving in the House.

On the Republican side, Reps. Howard “Buck” McKeon of Santa Clarita, chairman of the House Armed Services Committee, and John Campbell of Irvine have also announced plans to leave.

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A combination of factors — advancing age, Congress’ sorry image, hyper-partisanship, and political burnout — have contributed to the wave of congressional retirements.

But Waxman said that while “there are elements of Congress today that I do not like,” he was still enjoying the job. In a written statement to be posted on his official website, he added, “I still feel youthful and energetic, but I recognize if I want to experience a life outside of Congress, I need to start soon. Public office is not the only way to serve, and I want to explore other avenues while I still can.”

He expressed confidence that he would have won reelection had he run again — something most political handicappers agree on — but lamented the amount of time that he would spend campaigning and fundraising.