LANSING, Mich.—Barack Obama put forward a broad energy plan Monday designed to end U.S. reliance on imported oil within 10 years and shore up his standing amid a tightening White House race and high-anxiety over gas prices.

Obama’s proposal, though, includes two significant reversals of positions he has taken in the past: He had steadfastly fought the idea of limited new offshore drilling and was against tapping the nation’s emergency oil stockpile to relieve pump prices that have stubbornly hovered around $4 a gallon.

In a speech in Michigan, the Democratic presidential nominee in waiting also endorsed long-term work on hybrid cars and renewable energy sources.

“Breaking our oil addiction is one of the greatest challenges our generation will ever face,” the Illinois Democrat told a supportive audience as he embarked on a week to focus on energy issues. “It will take nothing less than a complete transformation of our economy,” he said. Presumed Republican nominee Sen. John McCain, speaking in Pennsylvania, again advocated more oil drilling off the U.S. coast. “Anybody who says that we can achieve energy independence without using and increasing these existing energy resources either doesn’t have the experience to understand the challenge that we face or isn’t giving the American people some straight talk,” he said. Obama and McCain are emphasizing solutions to the country’s energy woes as they seek an advantage in polling that shows the race competitive just weeks before their respective national nominating conventions and the final stretch of the campaign. The issue cuts across the diverse electorate, resonating with voters of all stripes, and it gives the candidates a way to talk both about domestic and foreign issues. High gas prices are causing food and transportation costs to surge and affect people’s everyday pocketbooks in a weakened economy, while the country’s dependence on foreign oil has emerged as a pivotal national security concern. Obama, who as recently as last month argued against tapping into the petroleum reserve located in caverns in Texas and Louisiana, proposed that the government sell 70 million barrels of oil from its stockpiles and said that releases from the reserve in the past have lowered gas prices within two weeks. Explaining his thinking, campaign energy adviser Heather Zichal said that Obama “recognizes that Americans are suffering.”