In an era of conservative dominance in the Republican Party's leadership, the leaders of the Republican Main Street Partnership (RMSP) say they are working to maintain a voice for party centrists. The group bills itself as a "coalition of fiscally conservative Republicans who share mainstream Republican values."

The RMSP will "add value to Republican efforts this year to keep the House of Representatives," said Virginia Rep. Thomas M. Davis III, a member of the organization's board of directors, who conducted a political briefing Wednesday that identified some of its top priorities in this campaign year.

Its premier goal may be to help moderate Republican congressional incumbents fend off conservative primary challengers.

The highest-profile contest in which the RMSP is involved is Pennsylvania's April 27 primary, in which four-term Republican Sen. Arlen Specter faces a serious challenge from conservative three-term Rep. Patrick J. Toomey.

Davis - who helped Republicans maintain their House majorities as chairman of the National Republican Congressional Committee during the 2000 and 2002 cycles - said the Pennsylvania race is "relatively close."

He also stated that the Senate seat "becomes very difficult to hold" if Toomey is the general election candidate against Rep. Joseph M. Hoeffel, the presumptive Democratic nominee.

Though Specter won re-election easily in 1998, Pennsylvania is a partisan swing state that narrowly favored Democrat Al Gore for president in 2000 and elected Democrat Edward G. Rendell for governor in 2002.

Specter entered the home stretch of the primary campaign with a big financial edge over Toomey - $9.2 million to $2.1 million in available cash as of Dec. 31.

And Specter is getting added financial assistance from the Main Street Individual Fund - a so-called 527 fundraising group that supports moderate Republicans. The fund, which can accept large contributions, operates independently of RMSP.

RSMP Executive Director Sarah Chamberlain Resnick said that the Main Street Individual Fund has spent $350,000 in support of Specter and could lay out $100,000 more. The fund has budgeted $1 million to spend on all races this cycle, Resnick said.

The RMSP supports candidates through its own political action committee, which gave $2,500 to Specter's campaign last month.

Allied against the RMSP in the Pennsylvania Senate contest is the conservative political group Club for Growth, which strongly backs Toomey. The Club aired a television ad that points out similarities in the voting records of Specter and Massachusetts Sen. John Kerry, the heavy favorite to win the Democratic presidential nomination.

Another top target for the RMSP is the March 2 Republican primary in California's 3rd District, where three-term Republican Rep. Doug Ose is retiring: His sister, businesswoman Mary Ose, is the RMSP's preferred candidate. Davis said that Ose is rising in the polls and approaching the front-runner, state Sen. Rico Oller. Former Rep. Dan Lungren (1979-89) also is a major contender for the seat in the heavily Republican district.

 Also on March 2, RMSP-supported Rep. Wayne T. Gilchrest has a primary against conservative state Sen. Richard Colburn in Maryland's 1st District. But the group does not regard that contest as highly competitive. "I'm not worried," Resnick said.

In Pennsylvania's 13th District - which Hoeffel is leaving open to run for the seat held by Specter - the RMSP's PAC is backing Melissa Brown, an ophthalmologist. Brown, who lost bids for the seat in 1998 and 2002, faces primary competition from state Rep. Ellen Bard.

Davis said both candidates are "fairly moderate," but that Brown "has earned this shot." Brown held Hoeffel to 51 percent of the vote in 2002 and came within 4 percentage points of winning.

Other RMSP-endorsed candidates are Rep. Johnny Isakson, the front-runner in the Georgia Senate primary for the seat left open by retiring Democrat Zell Miller; Adam Taff, a pilot who ran a close race against Democratic Rep. Dennis Moore in Kansas' 3rd District in 2002 and is vying with two more conservative Republicans for this year's GOP nod; Rep. George Nethercutt, the presumptive Republican Senate nominee against Democratic Sen. Patty Murray in Washington; and Reps. Sherwood Boehlert of New York's 24th District and Rob Simmons of Connecticut's 2nd District.

RMSP's PAC also plans to endorse former state Sen. Joe Schwarz in Michigan's 7th District, where Republican Rep. Nick Smith is retiring after six terms. Schwarz was a key backer of the 2000 presidential campaign of Arizona Sen. John McCain, who defeated George W. Bush in the Michigan primary that year.

The PAC is still weighing whether to support candidates in other races. These include Texas' 17th District, where three Republicans are running in the March 9 primary to earn a shot against Democratic Rep. Chet Edwards; Oregon's 1st and 5th districts, where several Republicans are running to challenge Democratic Reps. David Wu and Darlene Hooley; and Florida's 14th District, where there is a crowded GOP field to succeed retiring Republican Rep. Porter J. Goss.