DENVER -- With his wife by his side, Sen. Wayne Allard first told 7NEWS Monday that he is keeping his term-limit pledge and will not run for a third term in the U.S. Senate.

"There were a lot of people that talked to me about continuing to run in the Republican Party. We appreciate their confidence and everything. But, you know, I just feel that the prevailing thing that you got to keep in mind is your commitments. I kept all my campaign commitments, except for one, and now I've completed that one, and that is my term-limit pledge," Allard told 7NEWS.

Allard then made his official announcement on the steps of the Capitol about an hour later.

The 63-year-old Republican reached a decision after a family trip to Disneyland. His decision to keep his word about term limits may have stunned both detractors and supporters.

"Because I made a commitment to the people of Colorado that I favored term limits and I would support their position of term limits. As you recall, the people of Colorado passed a term limits provision, and it wasn't the people of Colorado who changed it, it was the courts that changed it," Allard sid. "I think term limits are just as appropriate today as it was when Colorado first talked about term limits, and that was in 1982, when I first ran for the state Senate."

Republicans have been pressing Allard to defend his seat. The party will be tied up defending the White House in 2008, and holding a seat in Colorado could be more difficult if Allard leaves it vacant.

Colorado's other U.S. senator, Ken Salazar, is a Democrat.

The Senate race is now wide open and expected to be hotly contested.

Democrats see the race as a chance to pick up another vote in Congress after wresting two House seats and a Senate seat from Republicans the past two years.

Democratic Rep. Mark Udall, a popular five-term congressman and son of former U.S. Rep. Morris Udall of Arizona, has said he will run for the seat.

Udall issued a statement saying he was not surprised by Allard's announcement "because I always assumed he would keep his word on term limits."

Another Democrat who has been mentioned as a potential candidate is Denver Mayor John Hickenlooper.

On the Republican side, former congressman Scott McInnis said he will run if Allard and former Gov. Bill Owens don't. Owens, a Republican, left office last week after term limits prevented him from running again.

McInnis issued a statement praising Allard but did not discuss his own plans.

Another prominent Republican, anti-immigration firebrand Rep. Tom Tancredo, also has been mentioned as a possible candidate. So have Attorney General John Suthers, who said through a spokeswoman it was premature to make a decision about 2008, and John Elway, the former Denver Broncos quarterback.

Allard said he would not choose sides in a primary. He said he announced his plans early to give Republicans time to prepare for the next election.

When Allard ran for the U.S. Senate in 1996, he pledged to serve only two terms.

"When I first announced for Congress, I made a pledge to be a citizen legislator and serve in the Jeffersonian ideal of public service where you serve for a period of time and then return to live under the laws you have helped enact," said Allard. "I also pledged to the people of Colorado, that if elected, I would serve no more than two terms in the United States Senate. Today, I am honoring both of those pledges to the citizens of Colorado."

His political strength came into question in 2006 when Time magazine ranked him as one of the five worst U.S. senators.

"In a Senate full of ambitious members, Colorado Republican Wayne Allard is so bland that his critics have dubbed him 'Dullard,"' Time said.

The article criticized him for "almost never" playing a major role in legislation despite being a Republican on the powerful Budget and Appropriations committees.

Allard's chief of staff, Sean Conway, criticized the Time ranking as "more like a popularity poll" and said it was based mostly on opinion.

A veterinarian with almost 16 years in Congress, Allard is known for his conservative voting record, especially for sponsoring a constitutional ban on gay marriage.

Allard added that he still has two years remaining in his term and he expects those two years to be two of the most productive, although his party has fallen into minority status.

"I have already introduced this year the first phase of my Colorado legislative agenda comprising 16 bills," said Allard. "In the coming weeks, I will be building on this agenda with the introduction of several more pieces of legislation. I intend my final two years to be my most productive of my congressional career and will continue to work just as hard for the people of Colorado my last two years in office as I have over the last 16 years."

Allardwas born in Fort Collins, received his veterinary medicine degree from Colorado State University, and had a veterinary practice in Loveland.