A new survey gives Timothy M. Kaine a narrow edge over George Allen in the fight to succeed retiring Sen. James Webb (D), as Allen picked up an endorsement from a key conservative ahead of the Republican primary.

Tim Kaine, left, and George Allen, right, (Steve Helber/AP)

The NBC News/Marist Poll gives Kaine (D) a 46 percent to 40 percent edge over fellow former governor Allen (R) among registered voters, a lead within the survey’s margin of error but wider than most other polls of the race.

A Washington Post poll released earlier this month showed the two men tied among likely voters at 46 percent apiece, and several other surveys have shown similar results. The only other poll to give Kaine a lead this big was the last NBC/Marist survey, which gave the Democrat a 9-point edge and drew criticism from Republicans. Similarly, a pair of Roanoke College polls giving Allen leads of 7 and 8 points were greeted skeptically by Democrats.

Before he can face Kaine, Allen has to fend off three opponents in the June 12 Republican primary. Allen is the heavy favorite in that contest, and on Thursday he got the public backing of Sen. Tom Coburn (R-Okla.), an influential fiscal conservative. Allen and Coburn served together in the Senate in 2005 and 2006.

“I’m proud to announce my support for George Allen,” Coburn said in a statement released by the Allen campaign. “He was one of only 14 Senators who stood with me when I led the effort to eliminate funding for the infamous ‘Bridge to Nowhere.’”

Coburn is a leading critic of earmarks, but Democrats have sought to paint Allen as a hypocrite on the subject, noting that he requested and voted for numerous projects during his term in the Senate. “Every single earmark I’ve gotten, I’m proud of,” Allen said in 2006.