Obama faces the worst economic crisis since Franklin D Roosevelt became president in 1932 in the midst of the Great Depression, when American unemployment hit 25%. If recession now is not to turn into another depression, the world needs Obama 2012 badges to say: "Yes, we could, and we did."

Fixing the economy is what America's voters most want from Obama. It far outstripped worries about Iraq, Afghanistan and other concerns in pollsters' surveys. And even as his victory tally climbed, so did the bad news. Figures revealed in October 240,000 Americans lost their jobs, pushing unemployment up to 6.5%. Detroit's carmakers, faced with sales down 32%, announced long winter shutdowns and went to Washington to beg for $50bn (£31bn) aid.

The International Monetary Fund revised its economic forecasts downwards, projecting the first contraction in the developed world's economies for half a century, with a 0.7% reduction in the US economy and a worse 1.3% decline in the UK. "It's not going to be quick and it's not going to be easy to dig ourselves out of the hole we are in," said the President-elect, acknowledging that the road to economic recovery is arduous. "But America is a strong and resilient country and I know that we will succeed if we put aside partisanship and politics to work together."

This isn't just political rhetoric. The moneyed rest of the world seems to agree for, despite America's Federal Reserve cutting interest rates to just 1%, the US dollar has steadily strengthened, indicating that others think the US is a safer bet for storing wealth than many other countries.

This is one shaft of brightness in an otherwise bleak outlook. The recipe for restoring economic health begins with where all the problems sprang from – the financial system. Though official interest rates have been brought just about as low as they can get, real interest rates charged to companies and individuals remain high as banks shy away from risk and try to restore their capital. The threat of further financial turmoil from recession-induced defaults on personal and corporate loans, which may feed through into the billions of derivatives built on these debts, just as sub-prime mortgage defaults corroded mortgage securities, is high. Obama may have to extend treasury secretary Henry Paulson's $700bn (£447bn) bail-out package.

To reduce the impact of recession, there is now general agreement that there will have to be a federal spending package of at least $150bn (£96bn) to provide an economic stimulus. Some think even that is too little and $500bn (£320bn) is needed to have a real impact. Then there is the question of fulfilling Obama's election pledges, chief among them his plan for a better federally funded health care system which may cost about £160bn (£102bn) a year.

That adds up to a whopping excess of spending over tax revenues, also falling because of recession, pushing this year's federal deficit of $450bn (£287bn) to probably $1,000bn (£639bn) next year and shoving America's national debt, which passed $10,000bn (£6,391bn) during the election campaign, higher still.

The offsets Obama has to mitigate this are pitifully small. A tax increase on the richest 5% of Americans is already spent on tax cuts for everyone else, and troop withdrawal from Iraq saves only about $80bn a year. So he is going to have to spend big and run up huge debts. The trick of restoring growth is to persuade people he also has a plan for eventually cutting that spending and the debt.

This trick was managed – on a much lesser scale – by Bill Clinton in 1992. It matters because America's ability to spend its way out of recession depends on foreigners' willingness to finance US debts, essentially by buying dollars and big chunks of the economy.

This matters to us for, just as the financial crisis began in the US, so the cure has to begin to work over there. Much though Gordon Brown would like to be able to produce a British solution to British problems, he can't do it without America's problems being solved. Does he think Obama can? You bet he prays he can.