Chicago (AP) Barack Obama is proposing tapping the nation's strategic oil reserves to help drive down gasoline prices.

His campaign says he supports releasing light oil from the emergency oil stockpile now and replacing it later with heavier crude more suited to the country's long-term needs.

Light crude is easier to refine into gasoline than heavier oil.

Obama is emphasizing energy and the economy in campaign stops this week in Michigan, Ohio and Indiana, beginning with a speech today in Lansing, Michigan. Gas prices over $4 a gallon have become a top issue in the presidential contest.

In the past, Obama has not advocated tapping the oil reserve, but a campaign spokeswoman says he has reconsidered because he “recognizes that Americans are suffering.”

Also today, the Obama campaign is unveiling a television ad that criticizes John McCain's energy policies.