WASHINGTON - California Rep. Henry A. Waxman on Thursday officially dethroned longtime Energy and Commerce Chairman John Dingell, upending a seniority system that has governed Democratic politics in the House for decades.

Rep. Henry A. Waxman, entering the caucus meeting Thursday. (Photo: AP) In a secret ballot vote in the Cannon Caucus Room, House Democrats ratified an earlier decision by the Steering and Policy Committee to replace the 82-year-old Dingell with his 69-year-old rival. The vote was 137-122 in favor of Waxman.

The ascension of Waxman, a wily environmentalist, recasts a committee that Dingell has chaired since 1981 with an eye toward protecting the domestic auto industry in his native Michigan. The Energy and Commerce Committee has principal jurisdiction over many of President-elect Barack Obama's top legislative priorities, including energy, the environment and health care.

"Seniority is important, but it should not be a grant of property rights to be chairman for three decades or more," Waxman said after emerging from the caucus meeting. 

Waxman's win is a big victory for environmentalists who want a more aggressive stance on global warming from the committee, and the vote showed the powerful hand of Speaker Nancy Pelosi, a Waxman ally, even though she officially remained neutral in the race. 

The ousting of the ultimate Old Bull - just three months before Dingell was set to become the longest-serving chairman in the House - is also a shot across the bow for other senior lawmakers who have enjoyed a comfortable and unchallenged ride in their chairmen's seats.

Waxman now says Dingell will be a "chairman emeritus" and will retain his Capitol office suite.

Waxman's challenge - launched the day after the election - had quietly divided members of the Democratic Caucus and forced wavering colleagues to cast a gut-wrenching vote. 

And the results Thursday could leave a bad taste in the mouth of Dingell supporters, who led a vocal effort to protect the chairman while Waxman's team led the quiet coup that led to Thursday morning's stunning vote. 

Dingell was confident heading into the vote this morning, but his vocal supporters were clearly overwhelmed by Waxman's behind the scenes lobbying for the chairmanship.

"Well, this was clearly a change year and I congratulate my colleague Henry Waxman on his success today," Dingell said in a statement. "I will work closely with him on the issues facing the Energy and Commerce Committee and for a smooth transition." 

In the closed door meeting, Dingell said, "I ask you to consider my accomplishments," according to the notes of someone in the room.

This plea, coming from a lawmaker who joined Congress during the Eisenhower Administration, was not enough to swing the newly-elected freshmen who helped propel Waxman to the chairmanship.

Waxman embraced the idea that he is part of a culture of change sweeping Washington.

"We are at a unique moment in history," he told reporters afterward.

Rep-elect Gerry Connolly of Virginia, who whipped the new members for Waxman, said 18 of the 26 members of his freshmen class had committed to the Californian before the vote. "It would be fair to conclude a large majority of the freshmen class was responsive to Waxman," Connolly said afterward.

Dingell and his backers touted the chairman's many achievements atop the Energy and Commerce Committee. But the most emphatic arguments were those made in favor of the seniority system.

In his nominating speech for Dingell, Georgia Rep. John Lewis warned the most senior Democrats that they might be next, should Waxman defeat the long-standing chairman, according to people in the room. Asked afterward what the vote means to the seniority system, Ways and Means Chairman Charles B. Rangel, 78, said, "It has been buried."

"I have enjoyed the seniority system," Rangel said. "It wasn't broken."

The question now is what will become of Dingell's most vocal supporters. Oregon Rep. Earl Blumenaur, a member of the committee, suggested some of the subcommittee seats could flip now that Waxman is in charge.

South Dakota Rep. Stephanie Herseth Sandlin, an outspoken Dingell supporter, said she was "very disappointed by the result."

Asked how long it would take the wounds to heal, Herseth Sandlin said, "It'll depend member-by-member."

Waxman was generally respectful of Dingell in his speech before the caucus, according to people who were in the room, but he took a few sharp jabs at the chairman. Iowa Rep. Bruce Braley, who gave one of Waxman's nominating speeches, went a step further, lashing out at Dingell for standing in the way of environmental reforms. He even complained that the speaker had to go around him to enact a renewable energy bill during the Democrats' first year in power.

The vote was tight up until the end, according to members and aides. There was a bloc of 30 or so uncommitted members heading into the vote that no one wanted to cast.

Before the vote, California Rep. Mike Honda said, "It feels like the temperature of the globe is going up a bit."

"There are a lot of mixed feelings in the caucus based on that vote," said Florida Rep. Kendrick Meek, a Dingell supporter. "We're just going to have to move on."

Waxman told reporters afterward that he had been considering a bid before the election. He called Dingell after the election to tell him he was running to replace his long-time rival. "He didn't agree with me that we needed new leadership," Waxman said. "I told him I was running and that the caucus would decide it."

"The caucus is responding to the call of the American people for change," Waxman said. "That was why senator Obama won. That's why many of the members that are here were elected in districts that had been held by Republicans in the past."

"I argued that I can deliver that change," Waxman said.

John Bresnahan and Ryan Grim contributed to this article.