By Bob Benenson and Michael Teitelbaum, CQ Staff

Maryland Rep. Wayne T. Gilchrest , a nine-term centrist unseated in this year’s Republican primary, this morning endorsed county prosecutor Frank Kratovil Jr. — the Democratic nominee — to succeed him. In doing so, Gilchrest broke formally with the campaign of Republican state Sen. Andy Harris, the strongly conservative candidate who ousted him in the Feb. 12 contest.

“For the 18 years I have been honored to represent the 1st District in Congress, I have always tried to make decisions based on principle rather than partisanship or politics,” Gilchrest said in his prepared remarks at the beginning of a conference call with reporters from the state capital of Annapolis.

He continued, “This decision is no different. I admire Frank’s integrity and independence. He will continue the moderate tradition of Maryland’s Eastern Shore.”

As Gilchrest has in the GOP, Kratovil positions himself as a centrist in Democratic ranks. The two-term state’s attorney in Queen Anne’s County — a portion of the Eastern Shore of the Chesapeake Bay where voters lean conservative — echoed a charge often made by Gilchrest that ideological “extremists” tend to dominate debates between the two major parties and hinder progress on legislation to address major national concerns.

Gilchrest deflected a question from CQ Politics about why he decided to make this announcement of the second day of the Republican National Convention in St. Paul, Minn. He said he had been tied up with travel, work and family obligations and will have a busy schedule as Congress returns next week from a month-long recess, so today was the best available date to him.

Though sources close to Gilchrest have long said a Kratovil endorsement was possible, Gilchrest told reporters today that he had only recently settled on his decision.

Still, the eastern Maryland congressman’s sharp break with his party contrasted with the show of unity on display at the convention in Minnesota as the party prepares to nominate Republican Sen. John McCain of Arizona. It provided a reminder of a rift that persists between the conservatives who generally dominate the party and more moderate officeholders and rank-and-file voters — especially from the increasingly Democratic-dominated Northeastern states such as Maryland — who complain that they have been marginalized within GOP ranks.

When asked about the issues on which he thinks his party needs to moderate its approach, Gilchrest named almost every major matter facing the nation’s policy-makers. “It’s about energy, farming, environmental issues, health care, foreign policy,” Gilchrest said. “The Republican Party has strayed from the mainstream and from being fundamentally competent.”

Supporters of Republican nominee Harris and party officials in turn sharply criticized Gilchrest’s cross-over endorsement.

“Voters are tired of Congress’ failed policies of raising taxes, increasing wasteful spending and failing to produce a comprehensive energy package. Andy Harris is the change we need in Washington and Frank Kratovil obviously represents more of the same,” said Harris campaign manager Chris Meekins. On Gilchrest, Meekins said, “For months we have known this was coming. Sadly, both of them support the liberal policies of Nancy Pelosi ,” a reference to the California Democrat who is House Speaker.

Maryland Republican Party Chairman Jim Pelura said, “While Congressman Gilchrest’s action is certainly not a surprise to us, it is disappointing. The Maryland Republican Party and Republicans in the 1st Congressional District have supported Wayne for years, and many Republicans will view his decision as a betrayal of that support.”

A number of Gilchrest supporters complain he did not get sufficient support from the party establishment in the primary, even though he ran with the endorsement of President Bush. Former Gov. Robert L. Ehrlich Jr., still the most prominent Republican figure in the state despite his 2006 defeat by Democrat Martin O’Malley, endorsed Harris over Gilchrest during the primary campaign.

Gilchrest, a low-key 62-year-old Vietnam War veteran and former teacher, has long stood out with Republican congressional ranks for his environmentalist stance. He has often broken with his party’s line during Bush’s presidency, including his criticism of the administration’s handling of the Iraq War.