Four Virginia Republicans running for U.S. Senate will meet in Falls Church Friday evening for the third and final debate before the June 12 primary.

GOP candidate Del. Bob Marshall (R-Prince William), second from right, talks during the first of three debates, in April in Roanoake. Other GOP candidates participating in the debate are, from left, former Virginia senator and governor George Allen, Chesapeake minister E.W. Jackson, and tea party leader Jamie Radtke. The winner of the primary will face former governor Tim Kaine in November. (Stephanie Klein-Davis/Associated Press)

A recent Washington Post poll showed Allen getting 62 percent of the vote among likely GOP primary voters. Marshall was next with 12 percent, and Radtke and Jackson had 5 and 3 percent, respectively.

The winner of the primary will face former governor Timothy M. Kaine, who faces no opposition for the Democratic Senate nomination.

The race — for the seat being vacated by retiring Sen. James Webb (D) — is expected to help determine the balance of power in the Senate.

In previous debates, Allen’s rivals have criticized his record as a single-term senator and governor, while Allen mostly focused on Kaine’s stints as governor and Democratic National Committee chairman.

Radtke, who has been the most aggressive against Allen, launched radio ads this week that labeled him as a big spender who as senator went along with the ways of Washington instead of challenging them.

Some Allen supporters said the ads, which called him “an election disaster waiting to happen,” went overboard.

A new issue could crop up in Friday’s debate, which come a week and a half after Marshall successfully pushed the General Assembly to block the nomination of a gay Richmond prosecutor for a city judgeship.

Marshall said he did not oppose gay judges per se. But he contended that veteran Richmond prosecutor Tracy Thorne-Begland, who came out as gay as a naval officer 20 years ago on “Nightline,” was unfit for the bench because he had challenged the military’s ban on gays openly serving in the military, advocated for gay marriage and lives with a partner with whom he is raising twins.

Marshall said that biography amounted to military insubordination and a challenge to the state constitution, which bans gay marriage and civil unions. Thorne-Begland’s life, Marshall said, “is a contradiction to the requirement of submission to the constitution”

Jackson has embraced the issue, putting out a statement mirroring Marshall’s stance last week. Radtke has not responded to a request seeking comment on the matter, while Allen has sought to strike a slightly more moderate stance than Marshall and Jackson. Allen has sought to align himself with Gov. Robert F. McDonnell (R), who objected to anti-gay discrimination in principle but refused to take a position on whether it had played a role in Thorne-Begland’s rejection.