LANSING, Mich. (AP) — In a reversal, Barack Obama proposed Monday that the government sell 70 million barrels of oil from its strategic petroleum stockpile to help reduce gasoline prices.

The Democratic presidential candidate said in a major energy speech that in the short-run the move could help drive down gasoline prices that now top $4 a gallon. Previously, Obama opposed tapping into the reserve, located in caverns in Texas and Louisiana.

Past releases from the reserve have "lowered gas prices within two weeks," Obama said.

The Illinois Democrat said U.S. politicians have failed for three decades to deal with the energy crisis and his GOP rival John McCain has "been part of that failure."

Obama called tapping the petroleum reserve a short-term response to a long-term problem.

"Breaking our oil addiction is one of the greatest challenges our generation will ever face. It will take nothing less than a complete transformation of our economy," he said. "This transformation will be costly, and given the fiscal disaster we will inherit from the last administration, it will likely require us to defer some other priorities."

Obama also reiterated his statement Friday that he could support limited new offshore drilling if it were needed to enact a compromise energy policy to foster fuel-efficient autos and alternative energy sources. He spoke warmly of a compromise proposed Friday by 10 moderate to conservative senators from both parties.

"Like all compromises, this one has its drawbacks. It includes a limited amount of new offshore drilling, and while I still don't believe that's a particularly meaningful short-term or long-term solution, I am willing to consider it if it's necessary to actually pass a comprehensive plan," Obama said. "I am not interested in making the perfect the enemy of the good particularly since there is so much good in this compromise that would actually reduce our dependence on foreign oil."

In remarks that elicited sympathetic boos from his supportive audience, the Illinois senator said of McCain, "Like George Bush and Dick Cheney before him, he sees more drilling as the answer to all of our energy problems, and like them, he's found a receptive audience in the very same oil companies that have blocked our progress for so long. In fact, he raised more than $1 million from big oil just last month."

Also on Monday, the Obama campaign unveiled a television ad that criticizes Republican John McCain's energy policies.

"After one president in the pocket of big oil we can't afford another," says the ad, referring to President Bush's previous work in the oil industry.

Obama is emphasizing energy and the economy in campaign stops this week in Michigan, Ohio and Indiana. Gas prices over $4 a gallon have become a top issue in the presidential contest and polls show McCain has used the issue to gain ground on Obama.

In the past, Obama has not advocated tapping the oil reserve, but campaign spokeswoman Heather Zichal said he has reconsidered. "He recognizes that Americans are suffering," she said.

The nation's strategic petroleum reserve contains 707.2 million barrels in salt caverns in Texas and Louisiana. It was last tapped shortly after Hurricane Katrina. Otherwise, President Bush has refused to use the reserves, saying they need to be left intact as an emergency stockpile. However, in the face of strong congressional pressure, Bush in June stopped filling the reserve until oil prices decline.

Obama's call for using the government reserve mirrors a proposal that has been pushed by congressional Democrats, but opposed by Republican leaders and the White House.