Rep. Wayne Gilchrest feels like he's back in the Marines, shining his belt buckle for inspection, only now he's trying to polish his conservative credentials in a hotly contested Republican primary.

The nine-term incumbent faces two serious challengers in Tuesday's GOP primary, in which he is a moderate under attack for allegedly not being conservative enough.

Gilchrest was one of only two Republicans to vote last year for a timeline for withdrawal from Iraq, and his criticisms of the Bush administration's conduct of the war have chafed many Republicans in the district.

Gilchrest and his primary opponents, state Sens. Andy Harris and E.J. Pipkin, are all trying to portray themselves as the true Republicans in the race.

Gilchrest campaigned recently with former U.S. House Speaker Newt Gingrich and former Maryland Lt. Gov. Michael Steele, two GOP favorites in the state. He's been talking up his experience in Congress, which dates to the days when Gingrich wielded the gavel.

"I'm glad to be here for Wayne. Wayne is an old friend," Gingrich told the crowd.

And in a Democratic primary in suburban Washington, Donna Edwards was back to give eight-term Rep. Albert Wynn another run, having treated him to a close race two years ago.

She lost by just 3 percentage points in 2006. If Wynn loses Tuesday, he would be the first incumbent to fall this primary season, though only one other state, Illinois, has included congressional races with its presidential primary elections so far.

Both candidates are black, and their district includes a large bloc of black voters in Prince George's County, one of the nation's most affluent majority-black communities.

"It's the bellwether of the black population around the nation," said Ronald Walters, a political scientist at the University of Maryland.

Edwards has criticized Wynn's vote in 2005 for a measure tightening bankruptcy rules, which she says has made it harder for struggling homeowners facing foreclosures. Prince George's has the highest rate of foreclosures in Maryland.

And continuing a major theme of her 2006 challenge, Edwards has pressured Wynn over his initial support for the war in Iraq.

Wynn has since spoken out against the war and has appeared at foreclosure prevention events, including one with the Rev. Jesse Jackson. He said that Edwards has exaggerated the effect of the bankruptcy bill on foreclosures and that he has worked to help homeowners struggling to pay their mortgages.

Harris and Pipkin both have proposed measures in the state legislature sure to curry favor with Republican primary voters. Harris proposed a state holiday to commemorate former President Ronald Reagan, and both Harris and Pipkin have proposed measures banning illegal immigrants from receiving in-state tuition.

"There's no question that in this race, all three candidates are trying to carry the conservative mantle," said Harris, who is backed by former Gov. Robert Ehrlich and the most conservative activists of the party.

After the primary, however, some expect the winning Republican will stop talking up his conservatism. That's because Democrats hold a slight advantage in party registrations in the district, though it has not sent a Democrat to Congress in a generation.

"I don't know if trying to prove you're the most conservative is necessarily going to win this race," said Salisbury University political scientist Harry Basehart.

You wouldn't know it from recent campaigning by the three leading Republicans. All three appear to be hoping to prove they're the best Republican.

"The 1st Congressional District is overwhelmingly right of center," Harris said. "It will elect a conservative Republican every time."

Still, Steele is worried about the Republican sniping in the 1st District primary, saying last week that the infighting is hurting Republicans' chances of regaining a congressional majority.

"We cannot get there if we continue to put bull's eyes on each others' backs and making a circular firing squad," he said.

The GOP victor will face the winner of a contested Democratic primary. Queen Anne's County State's Attorney Frank M. Kratovil Jr. is the front-runner, having raised more than twice as much money as his nearest opponent, Cambridge lawyer Christopher Robinson. Kratovil also has the endorsements of Gov. Martin O'Malley and other leading Maryland Democrats.

Gilchrest was unchallenged in 2006 on the GOP side and went on to beat a little-known Democrat with 68 percent of the vote.