ALBUQUERQUE -- U.S. Rep. Tom Udall says his decision to seek the Democratic nomination for the Senate seat being vacated by Republican Pete Domenici is not about ambition, but about ending deadlock in the closely divided chamber.

''I have not been aiming for this job, but I am aiming for a better New Mexico and a better America,'' he said Thursday as he announced his campaign.

After Domenici announced he would retire in 2009 because of an incurable brain disease, Udall initially said he would stay in the House. But his staff said he reconsidered after a ''groundswell'' of encouragement from New Mexicans.

''I went places and people said, 'Run, Tom, run. Get out there and do this.' There was truly a very sincere draft Tom Udall movement that made a big impact on me,'' he said in an interview.

Udall said Americans made a clear choice in the 2006 election that they wanted a change.

''It's time to let the will of the American people be heard. It's time for a new direction,'' said Udall, who pledged to work to end the war in Iraq, promote renewable energy, fully fund schools and strengthen homeland security.

He mentioned a bill he co-authored on global warming to cap carbon emissions and his other environmental work.

''Conservation is the legacy of the Udall family,'' said the candidate, who was joined Thursday on the podium by his father, former Interior Secretary Stewart Udall.

Udall will face Albuquerque Mayor Martin Chavez and Leland Lehrman, who publishes an alternative newspaper in Santa Fe, in the June primary.

A fourth Democrat, Jim Hannan, finance director of a Santa Fe housing trust, dropped out of the race and endorsed Udall.

Setting the tone of his campaign in a message to his fellow candidates, Udall said, ''Let us keep it positive and purposeful and focus on what really matters to the American people.''

Udall has been criticized for voting against funding for Los Alamos National Laboratory, a nuclear weapons lab in his congressional district that faces up to 750 job cuts.

He said he spoke against the spending cuts in the House Appropriations Committee and later offered an amendment to restore $200 million for the nuclear weapons lab to take its research in new directions the only New Mexico congressman to do so. On the final House vote, he said that before he voted to cut funding, he was assured there would be $600 million in new money that Los Alamos could compete for to do energy research.

Los Alamos needs to understand that the nuclear weapons complex will shrink, and it needs to diversify its mission, Udall said.

''My vote was about the jobs of the future,'' he said.

Chavez's campaign manager, Mark Fleisher, responded: ''That's the lamest excuse I've ever heard for negatively affecting thousands of New Mexico families.''

Fleisher said any decrease in lab funding would have a ripple effect on other businesses around the state.

Udall's decision to run for the first open Senate seat in New Mexico in 36 years leaves the state with three wide-open congressional races in 2008.

On the Republican side, Rep. Heather Wilson, who represents the Albuquerque-area 1st Congressional District, will face Rep. Steve Pearce of Hobbs, who represents the 2nd District that spans the southern half of the state.

Udall made his announcement at the National Hispanic Cultural Center in Albuquerque. He also has events scheduled in Los Lunas, Las Cruces, Silver City, Clovis, Las Vegas, Mora, Taos and his hometown of Santa Fe.

He has about $800,000 in a congressional campaign fund he can use for the Senate campaign.

Copyright 2007 The Associated Press. All rights reserved.