Sen. Charles J. Colgan was a pilot in World War II and, at 85, still has a lot of fight left in him. He keeps fit with a boxing-style workout, pummeling a heavy bag in his basement.

The Prince William County Democrat will need to keep his dukes up if he is to survive a slugfest of a reelection campaign. The 35-year Senate veteran finds himself in an unexpectedly close race with Republican challenger Tom Gordy, a 40-year-old Navy veteran and former congressional aide.

Virginia Republicans, who control the governor’s mansion and the House of Delegates, have long been focused on taking control of the Senate in Tuesday’s elections. But until quite recently, they were not optimistic about picking off Colgan, the state Senate’s longest-serving member and chairman of its most powerful committee.

A sour economy, anti-incumbent sentiment and the Republican tide that seems to be rising nationwide appear to be hurting Colgan, political observers say.

“This is one that I think became a big surprise even to the Republicans,” said Bob Holsworth, a retired Virginia Commonwealth University political scientist. “And it’s one where the Democrats believe they are going to hang on, but one that has brought a lot of consternation for Democrats. This would be a big upset.”

As the state GOP has grown more optimistic about its chances in the 29th Senate District, which includes parts of Prince William County, Manassas and Manassas Park, it has opened its checkbook. In the space of three weeks in October, the Republican Party of Virginia plowed $250,000 into Gordy’s coffers.

With help from a Democratic Senate political action committee, which showered $162,000 on Colgan last month, he still had the fundraising lead as of the end of October. But it was close: Colgan had raised $541,729 to Gordy’s $477,131.

Colgan was expected to be a shoo-in given his long tenure, reputation as a moderate and perch atop the Senate Finance Committee.

When he said last year that he might retire, U.S. Sen. Mark R. Warner (D-Va.) and state Senate Majority Leader Richard L Saslaw (D-Fairfax) persuaded him to run again to help preserve the party’s hold on the Senate. Republicans have to pick up only two seats to take control of the chamber.

“Colgan, over time, has been pretty broadly respected in a bipartisan way,” Holsworth said. “He’s often seen as kind of a moderate Democrat and not somebody Republicans would put the bull’s-eye on as a political target.

“It just happens to be what Republicans think is a pretty good year. . . . I think they thought this was a long shot, but it has become one of the key races to take the majority.”

Gordy has run an energetic campaign, promising to make the state more business friendly, reduce wasteful spending, improve schools and ease traffic woes. Gordy did not return calls seeking comment for this article.

Colgan, who in 2007 and again this year cut TV ads showing him boxing and running up steps “Rocky”-style, said he’s confident that he can win on his record of bringing jobs, transportation improvements and school funding to the district. But he also said the race has been tougher, and nastier, than any since he first won the seat in 1976.

Colgan maintains that Gordy has misrepresented his legislative record in a flurry of campaign mailings. Some indicate — falsely, Colgan said — that the senator has opposed incentives for businesses relocating to the state.

“I was in the airline business for 43 years,” Colgan said. “I started that business with one airplane. I sold the business in 2007 with 50 airplanes and 1,200 employees. Talk to me about creating jobs.”

Colgan said he ignored most of Gordy’s campaign mailings for much of the campaign, but last week his team issued a news release headlined “State Senator Colgan Outraged Over Gordy Falsehoods.”

“You get really tired of turning the other cheek,” Colgan said.