Bush's Republicans are fighting to keep their control of the US Congress, but polls and analysts suggest Democrats could capture the House of Representatives and possibly the Senate.

Republicans have sought to keep the focus on individual races, the war on terrorism and the economy rather than Bush, but Democrats appear to be gaining ground in their attempts to capitalize on the unpopularity among voters of the Iraq war.

"We have such a big mess in Washington. Bush is terrible and Iraq was a disaster," said 56-year-old Bill Caster of Kansas City, Missouri.

"It's time for a change. I want to fire every Republican in Washington," said Caster, who described himself as a political independent in a battleground state where Republican incumbent Sen Jim Talent is fighting a strong challenge from Democratic state Auditor Claire McCaskill.

Analysts say it all comes down to Iraq.

"The president is a bigger factor than usual this year and the biggest negative of his right now is the war in Iraq," said David Bositis of the nonpartisan Joint Centre for Political and Economic Studies.

Bush and the Republicans faced more bad news in the wake of the killing of 11 US soldiers on Tuesday in one of the bloodiest days in the war for US troops in a surge of attacks on American forces battling soaring sectarian violence.

"He (Bush) needs to hurry up and get out of there. He is losing too many lives. Why do they want to fight those people for the oil?," asked Paula Lange of New Orleans. She spoke in a trailer next to the home she is rebuilding after it was destroyed last year by Hurricane Katrina.

An ABC News/Washington Post poll released last week showed Bush was playing a bigger role in voting intentions than he did during the previous congressional elections in 2002, with expressed opposition to him as a factor more than doubling.

Thirty-five percent of the registered voters said their vote for Congress would be cast in opposition to Bush versus 18 percent who said it would be an expression of support for him. The rest, 47 percent, said he was not a factor.