Republican presidential hopeful Mitt Romney has repeated his attack on president Barack Obama's bailout of the auto industry, calling it "crony capitalism on a grand scale".

Two days before General Motors is expected to announce record profits, and two weeks ahead of the crucial Michigan primary, Romney used an editorial in the Detroit News to argue that the car industry should have gone through a "managed bankruptcy" rather than be given the bailout.

"Three years ago, in the midst of an economic crisis, a newly elected President Barack Obama stepped in with a bailout for the auto industry," Romney wrote. "The indisputable good news is that Chrysler and General Motors are still in business. The equally indisputable bad news is that all the defects in President Obama's management of the American economy are evident in what he did."

The decision to push such a politically difficult message is a gamble in a state he must win to retain any sense of momentum in his campaign. GM, the largest of the U.S. car firms, has added 17,600 jobs since August 2009. A study from the Center for Automotive Research last year said the car industry, including Detroit's big three manufacturers, would add nearly 200,000 U.S. jobs through 2015. U.S. manufacturers are expected to add 30,000 hourly or salaried employees in by 2015, and suppliers another 150,000.

Romney, the son of a former auto industry executive, has called Michigan his home state, and had been expected to easily win the vote. But a Public Policy Polling (PPP) poll on Monday put him 15 points behind Rick Santorum in Michigan, while a CBS News/New York Times poll on Tuesday put the two men neck and neck nationally.