Attorney General Kenneth T. Cuccinelli II of Virginia said Saturday that Gov. Bob McDonnell should consider resigning over the lavish gifts he and his family took from a political benefactor.

Mr. Cuccinelli, who is running to succeed Mr. McDonnell, went further than he has gone before in criticizing his fellow Republican. His remarks came during a debate with his Democratic opponent, Terry McAuliffe.

The governor is the target of state and federal investigations into influence peddling by Jonnie R. Williams Sr., on behalf of his company, Star Scientific. Mr. Cuccinelli also accepted gifts from Mr. Williams, and the attorney general has strenuously sought to distance himself from the governor, lest the scandal harm his campaign.

The subject came up late in the 90-minute debate, which was held in Hot Springs, Va., and streamed online, but it added some drama. Asked if Mr. McDonnell should resign, Mr. Cuccinelli said, “It is appropriate to ask him to think about it.”

Mr. McAuliffe accused the attorney general of failing in his “fiduciary responsibility” to Virginians because of his friendship with Mr. Williams and ownership of stock in Star Scientific.

Mr. Cuccinelli responded that an independent prosecutor cleared him of criminal wrongdoing last week. He tried to turn the tables by contrasting his transparency in asking for the investigation with Mr. McAuliffe’s refusal to release his full tax returns.

The debate, the first of several before Election Day, was an unusually negative confrontation after months in which the candidates traded barbs at a distance and through surrogates in their national party organizations.

They clashed over taxes, transportation spending, the national health care law and which candidate would bring more jobs to Virginia.

Mr. Cuccinelli accused Mr. McAuliffe of “flimflammery,” “influence peddling” and putting “Terry first.’’

Mr. McAuliffe shot back that his opponent “bullied” members of a state health board and was “the Trojan horse of Virginia politics” because of his “social ideological agenda.’’

Often, Mr. Cuccinelli returned to Mr. McAuliffe’s record as the founder of an electric car company, Green Tech, accusing him of bypassing Virginia to build a plant in Mississippi that had hired few workers and built few automobiles. “Terry had his choice,’’ he said, turning to his opponent on a stage in the Homestead resort. “You picked Mississippi. Run for governor there.’’

Mr. McAuliffe, a former champion fund-raiser for Bill Clinton and the Democratic Party, repeatedly shifted the topic to Mr. Cuccinelli’s record on social issues, saying he would drive away potential businesses from the state because of his conservative views on abortion and gay rights.

Mr. Cuccinelli said that as governor social issues would not be his priority. “My focus in this race is in growing jobs in the middle class,’’ he said.

Polls show the candidates closely tied. Although Virginia has twice sent Barack Obama to the White House, the electorate in nonpresidential years has been older, whiter and more conservative, which favors Mr. Cuccinelli. Mr. McAuliffe is trying to lift Democratic turnout by highlighting his opponent’s conservative social positions, while Mr. Cuccinelli seeks independent voters by questioning his rival’s business credentials.

Mr. Cuccinelli also wants to neutralize the deepening scandal around Mr. McDonnell. After hovering unacknowledged over the debate for an hour, Mr. McAuliffe finally introduced it. He bluntly called the relationship between Mr. Cuccinelli and Mr. Williams one of “quid pro quo,’’ a conclusion that goes further than anything made public so far.

He mocked Mr. Cuccinelli for staying at a lake house owned by the executive over Thanksgiving in 2010, a trip Mr. Cuccinelli valued at $1,500 in a financial disclosure report. “That’s a lot of turkey,’’ Mr. McAuliffe said.

In a closing statement, Mr. Cuccinelli said, “We’ve been rolling out positive policies emphasizing that we’re putting the middle class first.’’