Barack Obama on Monday said his proposed stimulus package would be as big as necessary to shore up the economy and lay the foundations for renewed growth, amid predictions it could match the government’s $700bn financial sector bail-out for size.

The president-elect made the pledge as he unveiled the team that will lead his administration’s response to the economic crisis, spearheaded by Tim Geithner, as Treasury secretary, and Larry Summers, as chief White House economic adviser.

Mr Obama said Mr Geithner would reach out to countries around the world to craft a “global response” to the financial turmoil and hailed his nominee’s “unparalleled understanding” of the challenges awaiting the new administration.

He gave few further details of the wide-ranging stimulus plan he proposed at the weekend but said it would be “of a size and scope that is necessary to get this economy back on track”.

Democratic leaders and economists have said the package, aimed at creating or saving 2.5m jobs within two years, could cost anywhere between $500bn and $1,000bn.

Mr Obama said his economic team would consult Congress, the Federal Reserve and even the Bush administration over the proposals with a view to the legislative process starting as soon as he takes office in January.

“We cannot delay,” he said. “Our families can’t afford to keep on waiting and hoping for a solution.” The president-elect has highlighted investment in infrastructure, “green” energy, school building and healthcare among the main components of the stimulus. The president-elect added he and President George W. Bush were in agreement on the need to do “whatever is required” to keep the financial system afloat and revealed the two men spoke yesterday about the new aid programme for Citigroup.

Mr Geithner has been at the heart of the Bush administration’s response to the financial crisis as president of the Federal Reserve Bank of New York but Mr Obama said his earlier experience in several international roles at the Treasury was just as important.

“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 said. “Tim's extensive international experience makes him uniquely suited for this work.”

The president-elect made clear that Larry Summers, former Treasury secretary in the Clinton administration, would also play a “critical role” co-ordinating economic policy as director of the National Economic Council, describing him as “one of the great economic minds of our time”.