McCain edges ahead of Obama for the first time as they duel over fuel prices

When voters describing themselves as "leaning" towards a candidate were counted, Mr McCain was narrowly leading Mr Obama by 47 per cent to 46 per cent, the Rasmussen Tracking Poll showed.

The influential survey showed that, without "leaners", the two candidates were tied with 44 per cent each. Last week, Mr Obama was ahead of his Republican rival by three points.

Driving seat: McCain at a rally of motorcycle riders in Sturgis, South Dakota. Concerns about the economy and fuel prices have given him a boost in the polls

However, due to a sampling error of two per cent either way, the poll suggests the candidates are tied.

It is thought that concerns over the economy have played into Mr McCain's hands  -  and observers also credit his aggressive advertising campaigning.

It is the first time that Mr McCain has shown any lead over Mr Obama  -  no matter how insignificant  -  since 3 June, when the Illinois senator saw off Hillary Clinton's challenge by sealing a majority of the delegates to the Democratic Party's presidential nominating convention.

Mr McCain is viewed favourably by 55 per cent of probable voters, compared with 51 per cent for Mr Obama, Rasmussen's poll showed. Other polls put the pair neck and neck.

Flip-flopping?: Mr Obama, pictured speaking here yesterday, has been accused of changing his energy policy

Mr Obama faced fresh claims of " flip-flopping" over a major change in his energy policy. He called for a "limited amount" of offshore drilling, and has also suggested tapping the strategic petroleum reserve. He has previously been opposed to both measures.

Mr McCain has pressed for offshore drilling and said work should start immediately if it is to have any effect on petrol prices in the next five years.

The issue of soaring fuel prices is expected to play a critical role in the election on 4 November.

In a reversal of his earlier policy, Obama said he would like to release up to 10 per cent of the 700 million barrels of oil that make up the petroleum reserve, kept in salt caverns in Texas and Louisiana.

Releasing the stored fuel would have an immediate effect at the petrol pumps, bringing lower prices for consumers, he said.

Mr Obama said: "We meet at a moment when this country is facing a set of challenges greater than any that we have seen in generations. And for too long, our leaders in Washington have been unable or unwilling to do anything about it.

"We should sell 70 million barrels of oil from our strategic petroleum reserve for less expensive crude, which in the past has lowered gas prices within two weeks."

But his plans were immediately criticised by the McCain camp, which accused him of changing his policy once again in an attempt to win public approval. They said he had performed a similar "flip- flop" on plans to pull troops out of Iraq.

Mr Obama had previously said he would withdraw all troops by 2010, but later amended the statement to say the troops would only come home if conditions in Iraq were suitable.