New Mexico's two Republican members of Congress will be gunning for the U.S. Senate seat that GOP stalwart Pete Domenici is vacating.

Steve Pearce, who represents Southern New Mexico's 2nd Congressional District, will run for the seat Domenici has held since 1973, The Associated Press has learned. Pearce's decision was disclosed Tuesday — 11 days after it was revealed that Heather Wilson, representing the Albuquerque-area 1st Congressional District, would seek the seat.

Meanwhile, though U.S. Rep Tom Udall's office is officially saying the Santa Fe congressman is sticking by his plan to run for re-election, a source in Congress told The New Mexican on Tuesday that Democrats in both Washington, D.C., and New Mexico are pressuring Udall to reconsider his decision not to run for the open Senate seat.

"It's no secret that there's lots of pressure," said the source, speaking on condition of anonymity. Some Democrats are not satisfied with the Democratic front-runner so far, Albuquerque Mayor Martin Chávez, the source said.

In recent days, at least two Web sites — tomudallforsenate.com and draftudall.com — have appeared urging Udall to take the Senate plunge.

In addition, 54 Udall supporters have contributed a total of $540 for a Udall Senate run on Act Blue, a Democratic fundraising Web site. According to his campaign finance report filed this week, Udall has more than $800,000 in his House campaign treasury — which legally could be used in a U.S. Senate race.

A SurveyUSA poll released last week showed Udall beating both Pearce and Wilson, while Chávez was behind both Republicans.

Pearce planned to send letters to friends and supporters today notifying them of his intent, a source close to Pearce told the AP, speaking on condition of anonymity to not detract from Pearce's formal announcement.

Pearce will publicly announce his candidacy in "the coming weeks," the source said.

Domenici is retiring at the end of his term next year because he has an incurable brain disease.

The announcement by Pearce and Wilson, coupled with Domenici's retirement, leaves at least three New Mexico congressional races in the 2008 election without incumbents. Democratic U.S. Sen. Jeff Bingaman of New Mexico won re-election last year.

In another development in the U.S. Senate race, former state Attorney General Patricia Madrid, who had considered running, told The New Mexican that she won't run for Domenici's seat. "I want to avoid a contested Democratic primary," she said.

She said she's been receiving many calls from national Democrats to run again for the District 1 Congressional seat, which she lost in a close race to Wilson last year. Although she previously has said she wouldn't run for that seat again, on Tuesday, she left open the possibility.

Madrid has been working for a national law firm, which has offices in Washington, D.C., and New York. She continues to reside in Albuquerque.

Madrid said she would back Chávez for the Senate "if he's the strongest Democrat." Chávez is the best-known Democrat in the Senate race so far. Several lesser-known candidates also are running: Democrats Don Wiviott, a Santa Fe developer; Jim Hannan, finance director of the Santa Fe Community Housing Trust; Leland Lehrman, who publishes an alternative newspaper in Santa Fe; and Republican Spiro Vassilopoulos, an oil industry investor.

Lt. Gov. Diane Denish is among the other well-known Democrats considering the Senate race.

Brian Sanderoff, an Albuquerque demographer who operates Research & Polling Inc., said Pearce's entry into the Republican primary will make the race more expensive for Wilson.

"Obviously, both will deplete their financial resources in a Republican primary rather than save them (for) the general," Sanderoff said.

The winner of the GOP primary likely would enter the general election with momentum and energy if the primary campaign is kept positive and above board, Sanderoff said. "If it gets nasty and the winner comes out wounded, it would be more difficult to build momentum for the general election," he said.

Pearce's southern district historically has tilted in favor of GOP candidates in statewide races, although Democrats account for about half of the registered voters.

Wilson represents a more moderate district, where Democrats have an edge by about 30,000 registered voters.

The Republican candidates must walk a fine line during the primary, because they will need a quarter of the registered Democratic voters in the state to win the Senate seat, Sanderoff said.

Wilson must appeal to conservative Republican primary voters, yet not turn off moderate suburban Democrats for the general election, Sanderoff said.

"Pearce has been a pretty conservative congressman who represents a conservative district, and he could maintain that message through the primary," Sanderoff said.

"But come the general election, the Republicans who have been successful in statewide general elections — Pete Domenici, (former Govs.) Gary Johnson and Garrey Carruthers — all of them have run pretty middle-of-the-road general elections," Sanderoff said.

Candidates who have run conservative general-election campaigns have been less successful, such as Republican Colin McMillan's unsuccessful 1994 bid for the U.S. Senate, Sanderoff said.

A Pearce-Wilson rivalry likely will energize voters for the primary election.

"The turnout in the primaries has no where to go but up because it has been so low," Sanderoff said. "The Republican turnout in the last two primaries has averaged 18 percent — just dismal — and the Democratic turnout hasn't been much better."

Pearce, 59, won election to the state Legislature in 1996, and earned a spot on the influential House Appropriations and Finance Committee, which handles the budget. In his second term, Pearce moved into the leadership as chairman of the House GOP caucus.

He sought higher office in 2000, but lost a race for the GOP nomination for the U.S. Senate.

Pearce entered the 2nd District race after 11-term GOP incumbent Joe Skeen announced his retirement in 2002. Pearce won the nomination in a five-way primary contest and defeated Democratic state Sen. John Arthur Smith in the general election.

In Congress, Pearce serves on the House Committee on Natural Resources, which oversees the Interior Department and handles federal water issues and management of public lands.

Pearce had about $582,000 in his congressional campaign account at the end of last month. Wilson had about $755,600.