Under Mr. Romney, Bain took advantage of new financial instruments like junk bonds, borrowing money to make big bets and, when they paid off, big returns. The firm also inserted itself into a variety of industries. It helped transform office supplies from a local business into a national one, by financing a business plan that turned into Staples.

“I don’t think of Mitt Romney in a C.E.O. context, because that’s not what he has done,” said Vin Weber, a former congressman from Minnesota advising Mr. Romney. “Mitt Romney has run a company where the sole mission was to look at companies and figure out how to make them more successful.”

Mr. Romney argues that the analytical skills he honed at Bain would be an enormous asset in the White House. He would use them, he suggests, to fix the economy’s problems while leaving alone its many healthy parts. His economic message is considerably more upbeat than that of the Democrats or of Mike Huckabee, his main rival in Iowa.

“I think the fundamentals of our economy are sound,” Mr. Romney said. “We are an innovative nation with enviable levels of productivity and high levels of education. And the combination is such that America has a strong and growing economy.”

As Mr. Romney argues in a PowerPoint presentation on the campaign trail, the main role of government is to allow the free market to do its work. One of his advisers, R. Glenn Hubbard, helped devise President Bush’s tax cuts. Another, N. Gregory Mankiw, succeeded Mr. Hubbard as the chairman of the Council of Economic Advisers under Mr. Bush.

At the same time, Mr. Romney tries to use his business experience to distance himself, gently, from Mr. Bush. He has lamented the response to Hurricane Katrina and portrays himself as pragmatic and competent. His time in the business world has made him willing to accept “three-quarters of a loaf,” Mr. Hubbard said, when the alternative is standing on principle and accomplishing nothing.

Mr. Romney also says that government has an important role to play  negotiating trade deals that are more favorable to this country, for instance, and setting up a well-functioning market for health insurance. He has proposed exempting from taxes the earnings on investments that are made by households earning less than $200,000. The plan would have a “double impact,” he says, helping the middle class while creating a bigger pool of capital to finance new businesses.