Democratic Attorney General Ken Salazar (search) said he will run for the Senate this fall, and Rep. Mark Udall (search) will drop out of the primary in what could be one of the nation's most competitive races, campaign officials said Wednesday.

The attorney general referred to his Hispanic heritage as he announced his bid to replace retiring Republican Sen. Ben Nighthorse Campbell (search).

"Today I want to help the people of Colorado and our country achieve the same American dream that I have been able to live," Salazar said. "I will do so through my service as a United States senator for the people of Colorado."

Udall and millionaire think tank founder Rutt Bridges both bowed out of the race and threw their support to Salazar.

Udall, 53, had announced his candidacy just one day earlier. On Wednesday, he deadpanned: "I think maybe this was the shortest Senate campaign in history."

The seat could be one of the most competitive races in the country and decide who controls the Senate, where the Republicans hold a 51-48 majority.

Salazar's decision comes a week after Campbell abruptly announced he would not seek a third term this fall because of health concerns. Republican Gov. Bill Owens (search) said Tuesday he will not run, leaving the party without a major candidate.

Udall said Tuesday he would be a candidate because he believed the nation "is on the wrong track." He touted his environmental record and promised to help bring U.S. troops home from Iraq.

The 50-year-old Salazar is a seasoned campaigner. He served as chief counsel to Gov. Roy Romer and once headed the state Department of Natural Resources. He was elected attorney general in 1998 and won another term in 2002.

Pollster Floyd Ciruli said Salazar has won two statewide races and is seen as more centrist than other Democrats. "He's the one person you don't want to run a primary against," Ciruli said.

Salazar is also handling investigations into the 1999 Columbine massacre that left 15 people dead and a look at whether criminal charges are warranted in the University of Colorado's recruiting scandal.

On the GOP side, Reps. Bob Beauprez, Tom Tancredo and Scott McInnis have all said they are interested in running for the Senate.

Beauprez spokesman Sean Murphy said Democrats were hurt by their wrangling over a candidate and said Beauprez will wait until next week to announce his plans, in time to prepare for precinct caucuses on April 13.

"We realize we don't have a lot of time," Murphy said.