MANCHESTER, N.H. — Mitt Romney on Monday dismissed intensifying attacks by his Republican rivals on his role at a corporate buyout firm, expressing confidence just a day before New Hampshire voters go to the polls.

The attacks came as Mr. Romney’s lead in New Hampshire appears to be slipping. A Suffolk University/7News tracking poll on Monday showed him still leading but with just 33 percent support, down from 43 percent in the same poll five days ago.

Newt Gingrich, after a campaign stop in Manchester, demanded that Mr. Romney explain in more detail the impact that Mr. Romney’s investment firm, Bain Capital, had on jobs. He said that Mr. Romney promotes his credentials as a businessman and should expound upon the buying and selling of companies.

“It’s a legitimate question about exactly what happened: Where did the money go? Who got the money? What happened to the people involved?” Mr. Gingrich told reporters. “He’s the one who went around and said he has 20 years experience — fine. Now let’s talk about the 20 years experience.”