ALBUQUERQUE — Republican Rep. Steve Pearce held a slim lead Tuesday over rival Heather Wilson in their race to become the GOP nominee to replace retiring U.S. Sen. Pete Domenici.

With 78 percent of precincts reporting statewide, Pearce led with about 51 percent of the vote to Wilson's 49 percent, according to unofficial results.

Domenici, a Republican who will retire in January after 36 years in office, will be replaced by either Pearce, Wilson or New Mexico's third congressman, Democrat Tom Udall, who ran unopposed in the primary.

The November general election face-off is likely to be one of the most closely watched Senate races in the country, with New Mexico's winner possibly tipping the balance of power of the Senate.

Wilson was in an upbeat mood as she arrived with her husband and daughter at an election night party thrown by the state Republican Party at an Albuquerque hotel. She was greeted by supporters cheering, "Viva, Heather!"

"Steve and I are personal friends," Wilson said. "We have differences on issues, and now it's up to voters to decide."

Pearce shook hands and greeted about 200 cheering supporters at his election night party across town with his wife and grown daughter by his side. He said he feels "excited. ... The polls are strong coming in."

For the primary, Wilson has campaigned as a moderate conservative who votes for the interests of New Mexicans rather than on a narrow ideological basis. She also stressed her ability to pull off razor-thin congressional wins in the Albuquerque-area 1st District, where registered Democrats outnumber registered Republicans.

Pearce has focused on his right-wing Republican credentials, including opposition to abortion rights and his staunch support of the war in Iraq. His main message to constituents has been his fiscal conservatism when voting on spending bills in Congress and his mission to go after wasteful federal spending.

His position was bolstered by an anti-tax conservative group called Club for Growth.Net, which spent $620,000 on television and Internet advertising against Wilson and collected $275,000 in contributions for Pearce.

The two Republicans attacked each other in TV ads. Pearce charged Wilson with being a liberal and paired her with Udall. Wilson accused him of voting to "mothball" Cannon Air Force Base and seeking to take away Social Security benefits from widows and orphans. Both denied the charges.

At times, the candidates reminded voters they are from the same party. In a lighter moment at a televised debate in Albuquerque, Pearce and Wilson both pledged to endorse the GOP primary winner.