Democrat Barack Obama says it is an "outrage" that taxpayers have to bail out Wall Street, but reluctantly agreed with Republican rival John McCain that a deal was vital to rescue the economy.

The White House hopeful said the $US700-billion ($A840 billion) deal being forged in marathon talks in Washington was no longer a "blank cheque" for the government, having taken stock of Democrat demands.

"If I feel that those are meaningful provisions that provide some constraints on how the Treasury operates and this is not going to be welfare for Wall Street, then my inclination is to support it, because I think Main Street is now at stake," Obama told CNN.

At a rally, Senator Obama, 47, mocked McCain's role in the delicate congressional negotiations on the government's $US700-billion bail-out request, which are being frantically finalised.

"You see, I think Senator McCain just doesn't get it - he doesn't get that this crisis on Wall Street hit Main Street a long time ago," he said, noting McCain's initial remark that the economy was fundamentally "strong".

"That's why he's been shifting positions these last two weeks, looking for a photo-op, and trying to figure out what to say and what to do," Obama told supporters in Detroit joined by his running mate Joseph Biden and their wives.

Democrats have accused McCain of scuppering an earlier tentative deal which seemed to evaporate on Thursday when he arrived back in Washington.

But McCain, 72, hit back that he had helped bridge a gap with House Republicans concerned at the unprecedented deal, which will be the biggest government financial intervention since the Great Depression.

Asked why he had rushed back to Washington dramatically suspending his campaign, McCain told ABC: "I came back because I wasn't going to phone it in.

"I saw that the House of Representatives was not engaged, that the Republicans in the House of Representatives were not engaged in the negotiations. I understand that.

"They're the most fiscally conservative people. And so I came back."

McCain also said he hoped to support the plan being finalised in Congress, after it had included some of his core demands, including greater oversight and protection for taxpayers.

"This is something that all of us will swallow hard and go forward with. The option of doing nothing is simply not an acceptable option," McCain said.

With recent polls giving Obama the edge just five weeks from the November 4 election, McCain, a veteran senator who once acknowledged that the economy is not his strength, has struggled to convince voters he can tackle the country's financial woes.

Neither McCain 72, nor Obama, 47, landed a decisive blow in Friday's first presidential debate at the University of Mississippi or committed a major gaffe, a verdict that benefits Obama given his slim lead in the polls.

An instant telephone poll by CNN and Opinion Research Corporation after the debate scored a win for Obama among 524 debate watchers. Asked who did the better job, 51 per cent said Obama and 38 per cent said McCain.

The Democrat had a yawning lead of 58-37 per cent on handling the economy, and a narrower edge of 52-47 per cent on the Iraq war, the pollsters said.