US President Barack Obama tried to put his Republican foe Mitt Romney on the defensive Thursday, accusing him of wanting to end tax credits for the wind energy industry and put at risk 37,000 jobs.

On the second day of a swing through battleground Colorado, Obama narrowed in on a local issue with the potential to move votes in the Rocky Mountain state, and in midwestern Iowa, which the president will tour next week.

"At a moment when homegrown energy is creating new jobs in states like Colorado and Iowa, my opponent wants to end tax credits for wind energy producers," Obama told a crowd of around 3,500 in the Rocky Mountain state.

"Think about what that would mean for a community like Pueblo. The wind industry supports about 5,000 jobs across this state.

"Without those tax credits, 37,000 American jobs, including potentially hundreds of jobs right here in Pueblo, would be at risk," Obama said.

The wind energy tax credit is due to expire at the end of the year and Obama wants to extend it. Romney's campaign has indicated he opposes such a move.

The row over wind power was the latest example of the way local issues can take on huge national prominence in a presidential election, as candidates pick their way through the state by state map seeking a path to the White House.

Obama said, as he cranked up his re-election campaign, that it was time to stop spending billions of dollars in subsidies for the profitable oil industry and to start investing in clean energy.

Romney has ridiculed Obama's plans to subsidize new generation clean energy projects, highlighting the failed solar energy firm Solyndra which went bankrupt after getting a half billion dollar government loan guarantee.

"In place of real energy, Obama has focused on an imaginary world where government-subsidized windmills and solar panels could power the economy," Romney said in a Columbus Dispatch newspaper article in March.

"This vision has failed. His promise of five million green jobs vanished as fast as the $500 million he gave to his campaign donors at now-bankrupt Solyndra."

Romney has pledged to slash regulations on the energy industry to speed up the exploitation of oil and gas reserves and to open up areas in the Gulf of Mexico, and the Alaska National Wildlife Refuge for drilling.