Del. Robert G. Marshall

In his announcement, Marshall ignored the crowded GOP field, including former senator George Allen, and went after the presumed Democratic nominee, former governor Timothy M. Kaine.

“I can beat Tim Kaine in the Nov. 6 general election,” Marshall said in a statement. “I already have a ‘can do’ record of challenging Tim Kaine and winning in the public arena on major economic and social issues, and I can do it again.”

Brandi Hoffine, a Kaine spokeswoman, said: “We welcome Del. Marshall to the race and look forward to contrasting our positive record of fiscal responsibility and sound economic management with the Allen/Marshall agenda that would rather re-litigate past disputes than find common ground on future challenges.”

Supporters began circulating petitions last week to place Marshall’s name on the June 12 primary ballot in the race to replace retiring Sen. James Webb (D).

Marshall, 57, said he was urged to get in the race while he campaigned in the fall for reelection to the House, where he has served since 1992.

“For the last two years, as I’ve spoken to groups throughout Virginia, conservative leaders and grass-roots activists in every congressional district have urged me to run, pledging their support in collecting petitions and securing the backing of primary voters,” he said.

Others in the GOP race include Jamie Radtke, former chairwoman of the Virginia Federation of Tea Party Patriots; Hampton Roads lawyer David McCormick; and Bishop Earl Jackson.

State Sen. Richard H. Black (R-Loudoun) will chair Marshall’s campaign.

“As a young Marine officer, I fought in the bloodiest campaign in the Vietnam War, so I’ve seen this nation in desperate straits, but never more desperate than it is today,” Black said. “We must elect patriotic leaders like Bob Marshall, grounded in the Constitution and with solid moral values.”

Marshall wrote the amendment to the Virginia Constitution prohibiting same-sex marriage, which was ratified in 2006, and the Virginia Health Care Freedom Act of 2010, the basis of Virginia’s federal court challenge of the federal health-care law. He also successfully challenged the constitutionality of a 2007 transportation bill that would have let unelected authorities impose taxes.

“I’ve been involved in some major fights in Virginia with some people who are maybe nice guys but don’t have such good policies,” he said.  “For example, Tim Kaine. I like him personally, but you judge his policy.”

Marshall almost defeated former governor James S. Gilmore III to capture the Republicans’ Senate-race nomination at a 2008 convention to run against former governor Mark Warner (D). The margin was less than one percentage point.

But Republicans have decided to hold a primary this year, not a convention, and that’s expected to benefit Allen, who is well known statewide.

“George Allen respects Delegate Marshall, and through the years they have had the opportunity to work together on a number of issues,” Allen spokesman Bill Riggs said. “Our campaign remains focused on building on the strong grass-roots support we have received throughout the commonwealth and George Allen’s positive message of proven, pro-growth solutions to reinvigorate the economy and ensure all Americans have the greatest opportunity to succeed.”

To get on the ballot, candidates have until March 29 to collect 10,000 signatures from across the state, including 400 from each of the 11 congressional districts.