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 new 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.

Not only did Obama push for drawing from the Strategic Petroleum Reserve, he also reiterated his changing position on offshore drilling — first revealed last Friday — suggesting that he could live with it if done in an environmentally sound way and as part of a bipartisan energy compromise.

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."

The reserve contains 707 million barrels in salt caverns in Texas and Louisiana. It was last tapped shortly after Hurricane Katrina in 2005.

Obama said that U.S. politicians have failed for three decades to deal with the energy crisis, and that McCain has been "part of that failure." He called tapping the petroleum reserves a short-term solution to a long-term problem.

"Like George Bush and Dick Cheney before him," Obama said of the Arizonan, "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 one million dollars from big oil just last month."

Also on Monday, the Obama campaign unveiled a television ad that criticizes McCain's energy policies. "After one president in the pocket of big oil we can't afford another," says the ad, referring to Bush's previous work in the oil industry.

Both candidates have moderated their positions since earlier this year. McCain abandoned his past opposition to drilling on the Outer Continental shelf and now is an aggressive advocate of such drilling.

"We're not going to achieve energy independence by inflating our tires," the Republican told employees at the National Label Co. in Lafayette Hill, Pa. Part of Obama's energy plan calls for consumers to fully inflate their tires for improved gas mileage.

McCain also called on Obama to join him in calling for Congress to return from its August recess to pass a comprehensive energy policy.

Gas prices have risen steadily as an issue since last November, according to a recent AP-Yahoo News poll. The issue rose to second place after the economy more broadly.

Obama said it was his "single overarching goal" to end U.S. reliance on oil from the Middle East and Venezuela over the next ten years, a project whose government pricetag he put at $150 billion.

The petroleum reserve is capable of releasing about 4 million barrels a day. It's unclear what impact such release might have on global oil prices, or costs of gasoline at the pump. But a clear signal by the United States to use its emergency reserve to a significant extent could put downward pressure on oil markets at least for a time, energy experts say.

In 2000, President Clinton used a similar "swap" of government oil as proposed by Obama, making available 30 million barrels because of concern over rising prices and supply worries in advance of that year's winter heating season. The move at the time was criticized by Republicans as an attempt to help then Vice President Al Gore's presidential bid.

Obama said that, under his plan, oil companies would bid to borrow easily refinable light sweet oil from the reserve, and replace it later with heavier oil.

Elgie Holstein, an Obama energy adviser, said that, while fewer refineries now are capable of refining the heavier stuff into gasoline, in the future that won't be the case.