LONDON, May 1 (Reuters) - U.S. President George W. Bush and British Prime Minister Tony Blair were determined to topple Saddam Hussein at least nine months before they launched the war in Iraq, British documents leaked in a Sunday newspaper say.

The secret documents could have a late impact in Britain's election next Thursday, in which Iraq -- and whether the prime minister told the truth when making his case for war -- has resurfaced as an issue in the final week of campaigning.

Blair has always maintained that he did not commit Britain to attacking Iraq until Saddam had been given a final chance to abandon banned weapons, and that "regime change" -- overthrowing Saddam -- was never his aim.

Despite hostility to Blair over his Iraq policy, polls show he is likely to win a third term in the election, though his huge parliamentary majority is expected to shrink.

Blair has been careful to say he believes the election result may still be in doubt. In an interview with the Observer newspaper, he urged anti-war voters not to cast a protest vote.

"There will be people who will feel very, very strongly over Iraq. But if they vote Liberal Democrat in a seat where the Conservatives are second, it is not policy on Iraq that will change -- it's the policy on the economy, on the health service, on schools, on the minimum wage," he said.

The Sunday Times printed what it said were secret minutes of a top-level cabinet meeting held in July 2002 to discuss Iraq, nine months before the invasion.

According to the minutes, Blair spoke to his cabinet explicitly in terms of toppling Saddam.

"If the political context were right, people would support regime change," Blair is recorded as saying. "The two key issues were whether the military plan worked and whether we had the political strategy to give the military plan the space to work."

Foreign Secretary Jack Straw said the case for war was "thin" because "Saddam was not threatening his neighbours and his WMD (weapons of mass destruction) capability was less than that of Libya, North Korea or Iran."

Straw proposed giving Saddam an ultimatum to allow in U.N. weapons inspectors, provoking a confrontation that would "help with the legal justification for the use of force."

Britain's spy chief, Sir Richard Dearlove, fresh from a trip to Washington, had concluded that war was "inevitable" because "Bush wanted to remove Saddam through military action", and "intelligence and facts were being fixed around the policy".

Blair ordered his chief of defence staff, Sir Michael Boyce, to present him with war plans later that week, the minutes said.

IRAQ SLOW TO EMERGE AS ELECTION ISSUE

Although many in Britain opposed the war, it has been slow to emerge as an election issue because both Blair's Labour party and the main opposition Conservatives backed it.

But the Conservatives have used the case Blair made for war to attack his credibility, and they hope some traditionally left-leaning Labour party supporters will swing to the anti-war third party, the Liberal Democrats.

The Sunday Times document was the second major Iraq leak to emerge in the final week before the election. Last week Channel Four news leaked advice to Blair in which the attorney general raised doubts about whether the war would be legal.

Blair's Downing Street office declined to comment on whether the minutes leaked to the Sunday Times were genuine, but said the meeting took place before the U.N. Security Council resolution that provided the basis for Blair's case for war.

"This was before the decision to go down the U.N. route, and before resolution 1441 on which the attorney general based his judgment," a spokeswoman said. "The circumstances therefore quickly became out of date."