MANCHESTER, N.H. — With just 21 days to rescue a political career teetering on the brink, Rep. Carol Shea-Porter (D) took the fight to Republican challenger Frank Guinta on Tuesday afternoon, repeatedly lashing out at the former Manchester mayor during a debate that was intense throughout and nasty at times.

At the end of the hour, the two-term incumbent had asked far more questions of Guinta than the moderator in a matchup that wasn’t supposed to include direct interaction between the candidates.

“What you’re doing is attacking me on just about every single issue,” Guinta said at one point, shortly before Shea-Porter fired another shot: “You sound like a victim. You need to be a leader, not a victim.”

A former social worker who shocked political observers by knocking off Rep. Jeb Bradley (R) in 2006, Shea-Porter trailed Guinta by 10 points in two independent polls released in the past two weeks. The race has also attracted a flood of independent expenditures recently: more than $1 million since Sept. 25, exclusively on the Republican side.

The tone of Tuesday’s debate, sponsored by AARP New Hampshire and the Greater Manchester Chamber of Commerce, was so tense that those gathered inside the New Hampshire Institute of Politics at Saint Anselm College shifted uncomfortably in their seats at times.

For example, when asked by a panelist whether he supported $2 million in federal funding for a local transportation project favored by the business community, Guinta said he was concerned that the proposal might not be effective.

Shea-Porter said she was in favor and noted that Guinta hadn’t directly answered the question.

“I support the notion of trying …” Guinta responded, before being cut off.

“Do you support the project?” she asked again.

“Carol, we have a situation where we have debt and deficit …”

“Do you support the project?”

“I’m being asked to spend more money without knowing whether it’s going to be profitable …”

“We’ll take that as a ‘No,'” Shea-Porter snapped as the moderator, positioned between the candidates, looked on.

It was much the same when the discussion turned to Social Security, tax cuts and the stimulus package.

While Guinta was on his heels for much of the debate, he offered at least one pointed remark of his own:

“When are you going to stop blaming George Bush?” he asked. “When are you going to take responsibility for the four years you’ve spent in Congress?”

Before the candidates clashed inside, more than 100 activists from both camps faced off outside in a scene that felt more like the parking lot at a college football game.

The crowd had gathered before 10 a.m. for a debate set to begin at 11:30 a.m., and there was near-constant screaming from dueling bullhorns. Guinta supporters rattled handmade noisemakers. The chanting from both sides was angry and loud.

“Carol Shea-Pelosi,” the Guinta supporters shouted.

“Hey Frank, what’s in the bank?” Shea-Porter’s volunteers responded, a reference to questions about Guinta’s personal finances raised during his GOP primary.

The candidates are scheduled to debate twice more before Election Day.