Barack Obama effectively took control of the US economy - two months before he takes office - by declaring that his plan to confront the financial crisis "starts today".

As he unveiled his new economic team, Mr Obama struck a very different note from the diffident election winner of three weeks ago who stressed that America is led by only "one president at a time".

Today, he appeared fully aware that the US and global markets are looking to him, not President Bush, for solutions to the deepening crisis.

Continuing the quickest White House transition of modern times, forced upon him by the speed at which the US is plunging into recession, Mr Obama stepped aggressively into what appeared to be a growing power vacuum in Washington over the economy.

Giving the outlines of a massive stimulus package to "jolt the economy back on track", Mr Obama stressed the need to act "swiftly and boldly". He said: "That work starts today, because the truth is, we don't have a minute to waste."

At a press conference in Chicago, Mr Obama formally announced his nomination of Timothy Geithner, 47, the president of the Federal Reserve Bank of New York, as Treasury Secretary, and Larry Summers, Bill Clinton's former Treasury Secretary, as director of the National Economic Council, his chief White House financial adviser.

Mr Obama refused to specify how much his stimulus package will cost, but some leading Democrats on Capitol Hill are now calling for a huge injection of cash of up to $700 billion.

The president-elect repeatedly stressed the urgency of the situation and spoke of an economy "trapped in a vicious cycle" as he made clear his expectation that Congress will have a plan ready for him to sign into law as soon as he is inaugurated.

"We know this won't be easy and it won't happen overnight," Mr Obama warned.

"The reality is that the economic crisis we face is no longer just an American crisis, it is a global crisis - and we will need to reach out to countries around the world to craft a global response."

He added that on January 20, he wants to "hit the ground running".

Mr Obama spoke shortly after being consulted by Mr Bush and Henry Paulson, the current Treasury Secretary, over their decision to bailout the stricken Citigroup. The move effectively gave a US government guarantee over the the bank's potential $306 billion losses on high-risk assets - the largest bailout yet. The bank was given an immediate injection of $20 billion.

Mr Geithner has already been working for months with Mr Paulson on the Wall Street rescue plan and both he and Mr Bush appear increasingly willing to cede the ground to Mr Obama and his team, as they recognise the importance that the response to the crisis largely lies now in the president-elect's hands.

Mr Obama said Mr Geithner offered an "unparalleled understanding of our current economic crisis, in all of its depth, complexity and urgency".

Mr Summers, considered one of the most brilliant economic minds in the US, will be a particularly influential adviser to Mr Obama and is a leading proponent for a massive and bold stimulus plan. Last week he said any such scheme would have to be "speedy, substantial and sustained".

"I am glad he will be by my side... and I will rely heavily on his advice as we navigate the unchartered waters of this economic crisis," Mr Obama said.

Mr Obama also named Christina Romer as director of the Council of Economic Advisers and added Melody Barnes to his economic team, a group that he said offered "sound judgment and fresh thinking".

Mr Obama has already, informally, put together the principal players in his national security team, including Hillary Clinton as Secretary of State. He has acted with almost unprecedented speed. Mr Clinton did not make his first transition announcement until mid-December 1992.

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