Barack Obama accused John McCain of being in the pocket of the big oil companies that were making record profits while US drivers were suffering, in an effort to regain the initiative after a week of attacks wiped out his lead in the polls.

With the faltering US economy – and petrol prices in particular – now the top issue among voters, the two candidates began the week concentrating on their proposals to reduce the dependence that America has on Middle Eastern oil, a subject that both believe could tip the election their way.

Mr Obama announced a sweeping energy plan during a speech in the battleground state of Michigan, and released an advertisement linking Mr McCain to President Bush, whose approval rating is at a record low.

Mr McCain has received $1. 3 million (£662,000) in campaign contributions from the oil industry, according to the nonpartisan Centre for Responsive Politics.

“After one president in the pocket of big oil, we can’t afford another,” the announcer on the advertisements for Mr Obama said.

The McCain campaign responded quickly, pointing out that Mr Obama’s boasts of taking no contributions from oil companies is misleading because he has received $400,000 in contributions from oil industry employees.

Aides to the Republican also accused Mr Obama of hypocrisy because he voted for Mr Bush’s 2005 Energy Bill, which gave $14.5 billion in tax breaks to oil companies – legislation that Mr McCain opposed.

The energy issue is dominating voter surveys. It is one of the few areas where Mr McCain believes he has the edge because of his recent decision to reverse course and support expanded oil drilling off the US coastline, a policy that Mr Obama opposed. The Arizona senator repeated his calls for offshore drilling last night.

In a series of polls by Quinnipiac University in Connecticut, voters in six of the seven largest swing states said that the energy policy of a candidate was more important to their choice of president than their views on the war in Iraq. By two to one, US voters – who until recently largely opposed offshore drilling – now back oil exploration on the Outer Continental Shelf.

Aware of how quickly the attitudes of voters are shifting, Mr Obama changed position. After long opposing such a move he called for tapping into the US strategic oil reserve as a short-term way to bring down petrol prices. He also said that he would be open to the idea of offshore drilling if it were part of a broader energy Bill aimed at funding alternative energy sources.

In his speech Mr Obama promised a windfall tax on the soaring profits of oil companies to finance a $1,000 per family rebate to help with high fuel costs. He pledged to cut consumption so that within ten years the US could save more oil than it currently imports from the Middle East. He said that he would create five million jobs by investing in clean energy schemes.

A windfall tax was imposed on oil companies by Jimmy Carter late in his presidency. It prompted oil companies to cut back on production and was repealed by Ronald Reagan in 1988.

Mr Obama again decried the idea of offshore drilling and said that it represented only 3 per cent of the oil reserves in the world in a country “that uses 25 per cent of the world’s oil”.

He also cited the public campaign mounted last month by T Boone Pickens, an oilman from Texas who has produced a plan to wean America off oil through alternative energy such as natural gas, wind and solar power. Mr Pickens, a Republican who funded the Vietnam Swiftboat attack campaign against John Kerry in 2004, appeared to have undergone a Damascene conversion on the oil issue.

He said that in 1970 the US imported 24 per cent of its oil – and that today it imported more than 70 per cent. “This is one emergency we can’t drill our way out of,” Mr Pickens said.

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