LONDON - World leaders on Thursday clinched a $1.1 trillion deal to combat the worst economic crisis since the Great Depression, and tightened the rules to stop it happening again.

At a G20 summit, they agreed to publish a blacklist of tax havens that could lead to sanctions, and for the first time to impose oversight on large hedge funds and credit rating agencies.

Today's agreement begins to crack down on the cowboys in financial markets that have brought global markets undone, with real impact on jobs everywhere, Australian Prime Minister Kevin Rudd said.

British Prime Minister Gordon Brown, the summit host, declared: This is the day that the world came together, to fight back against the global recession. Not with words, but a plan for global recovery and for reform, and with a clear timetable.

Markets, desperate for good news when the global economy is shrinking for the first time since World War Two, reacted positively to the imposing headline numbers.

Brown said governments had committed $5 trillion to public stimulus of the economy this year and next, before even taking into account the extra commitments from the summit in London.

He did not say how that squared with the stimulus estimate he gave just a day earlier -- of about half that amount.

It seems like they're throwing out huge numbers on stimulus, but it's unclear whether this is just double counting things that have already been spent, or whether it's actually gotten new commitments, and follow-up is going to be key, said Steven Schrage, from the Center for Strategic and International Studies in Washington.

Either way, the index of top European shares was up 5 percent after Japan's Nikkei gained 4.4 percent. On Wall Street, the Nasdaq was up 3.5 percent and the Dow Jones 3.3 percent. The price of oil topped $52.

Economists warned against euphoria.

The IMF funding is more than expected, and in so far as that means there is a larger pot of money available to bail out troubled economies that is good news. But these troublespots, particularly in Eastern Europe, are still there and this will not make them go away overnight, said Nigel Rendall, emerging market strategist at Royal Bank of Canada.

Brown conceded that there were no quick fixes but said the decisions would shorten the recession and save jobs.

The G20 said in a communique the measures taken would raise world output by four percent by the end of next year.

SARKOZY SMILES TOO

French President Nicolas Sarkozy said the results were beyond what could have been imagined and the world was moving on from the Anglo-Saxon model of finance.

Germany's finance minister welcomed the fact that no obligation was agreed for countries to adopt further stimulus packages. The issue had created tension in the summit build-up, with Washington favoring such packages and Paris and Berlin preferring to let earlier measures take their course.

Addressing a key demand from France and Germany, Brown said the leaders agreed there will be an end to tax havens that do not transfer information on request. The banking secrecy of the past must come to an end.

Switzerland and a host of other financial centers under fire over bank secrecy have announced in recent weeks that they will shift toward international standards of information disclosure.

Brown said the G20 leaders has committed on the day to new resources of $1.1 trillion that would be made available to help the world economy through the International Monetary Fund and other institutions.

This included 250 billion dollars of IMF reserve units called Special Drawing Rights. This is available to all IMF members, Brown said. In addition, the IMF would see its own resources tripled, with up to $500 billion of new funds, of which $40 billion would come from China.

The G20 asked the IMF to speed up sales of gold as well to raise funds to help the poorest countries, Brown said. And it agreed a trade finance package worth $250 billion over two years to support global trade flows, which have shrunk under the impact of the credit crunch.

The tax haven issue had threatened to be a stumbling block to agreement, with France and Germany demanding a crackdown on jurisdictions whose bank secrecy laws they portrayed as enabling the rich to dodge taxes at a time of economic hardship.

Since Bretton Woods, the world has been living on a financial model, the Anglo-Saxon model -- it's not my place to criticize it, it has its advantages -- clearly, today, a page has been turned, France's Sarkozy said, referring to the landmark conference that created the post-war economic order.

In the United States, meanwhile, an industry body announced a major change to accounting rules that would give banks more flexibility on how they value toxic assets. This would relieve pressure on banks with impaired balance sheets, which has been a major driver in financial market distress.

The change in the Financial Accounting Standard Board rules helped fuel a stock market rally.

(Writing by Brian Love, editing by Mark Trevelyan)

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