Promising bipartisanship while vigorously attacking each other’s parties — and each other — the two candidates for an open congressional seat in Northern Virginia clashed Wednesday over transportation, education and energy policy.

Fairfax County Supervisor John Foust (D) described state Del. Barbara J. Comstock (R) as someone with an “extreme right-wing agenda” and “a history of extraordinary partisanship.” His own career, he said, showed a history of “working across the aisle.”

Comstock’s line of assault was best encapsulated by a quote from Margaret Thatcher that she paraphrased: “If you want something said, ask my male colleague. If you want something done, ask me.”

Foust, she argued, was a lightweight with no record of accomplishment who “goes so far as to attack me personally and say that I’ve never had a real job or I don’t know anything about real jobs.” In contrast, she pointed to her own work in Richmond to bring more data centers to the area, encourage teleworking and eliminate mandatory labor agreements on state-funded projects.

She defended her vote against the state’s landmark transportation law in 2013, saying it was “a tough call” but that she ultimately thought the new taxes were disproportionately hard on Northern Virginia.

“The transportation bill literally is a gamechanger,” Foust replied. “It costs more in Northern Virginia because we get a whole lot more.” He lambasted Comstock for going to a ribbon-cutting for the opening of the Metro’s Silver Line, funded in part by that legislation, saying she “is now apparently taking credit for it after voting against it.”

Overall, he argued, Comstock was for small measures like tax credits but against the big investments in infrastructure and education needed to spur economic growth. Comprehensive immigration reform, he said, was another piece of legislation that would make a major difference in the economy. “She does not believe in comprehensive immigration reform,” he said. “I do.”

Comstock countered that Foust “thinks that the answer to many and almost all of our problems is to raise taxes.” On the contrary, she said, tax cuts and fewer government regulations are the keys to a healthy economy. She repeatedly emphasized her support for offshore drilling and fewer environmental and labor regulations. Foust said he supported the Environmental Protection Agency’s efforts to curb carbon emissions, balanced with economic concerns.

On immigration, Comstock said she supported securing the border first and then passing reform piece by piece.

“FedEx can track packages coming in here all the time,” she said. “We can track people who are coming into the country.”

Represented by retiring Rep. Frank Wolf (R) for the past three decades, the Republican-leaning, increasingly diverse suburban district has been targeted as a potential pick-up opportunity by national Democrats. The race has also attracted attention from both allies and antagonists of the Clintons, whom Comstock investigated as part of Republican scandal probes in the 1990s.

Referring to a Washington Post article, Comstock noted that her investigations began when she was working as an aide to Wolf and several constituents complained that they had been wrongly fired by the White House Travel Office.

“I’m proud that we went to bat for” those employees, she said. “I’m proud of that work.”

The debate questions came from a panel of local business leaders, convened by the trio of local chambers of commerce. Abortion, which has been an issue in one of Foust’s ads and was a topic at their previous debate, came up only in his closing statement, when he argued that “women’s health care . . . is an issue that is relevant to our economy.” Comstock and other Republicans, he said, wanted women to “bring their business here and leave their choice behind.”

Throughout the debate, Comstock smiled warmly at the audience, occasionally leaning forward to make a point or tilting her head skeptically when under attack. Foust seemed less relaxed, often fumbling a bit for words and looking at his notes.

But following the debate, Foust spent a chunk of time speaking to reporters. Comstock, in contrast, declined; a reporter from ABC7/Channel 8 attempted to interview her on her way out of the debate hall but was blocked by her campaign manager.