NEW YORK (AFP) — Global markets were torn by doubts over a huge US rescue plan Wednesday as the FBI probed top Wall Street names, the Federal Reserve gave more crisis help and the IMF chief issued a stark warning.

Mortgage firm Fannie Mae - along with other finance giants - is being probed by the FBI over allegations of fraud

IMF director general Dominique Strauss-Kahn told a German newspaper that European banking was stronger than the crisis-ravaged US sector but "it might be adviseable for the Europeans to prepare for the worst-case scenario."

Stocks wobbled in London, gaining 0.17 percent at mid-day in line with feverish European trading after a closing rise of 0.20 percent in Japan.

The main support came from legendary US investor Warren Buffett who announced a 5.0-billion-dollar investment in humbled Wall Street bank Goldman Sachs.

But the dollar fell on arguing among US policymakers over a 700-billion-dollar government rescue plan for financial markets.

The Federal Reserve central bank offered another 30 billion dollars to dollar-starved foreign markets via central bank "swap" deals, to a new total of 277 billion dollars, because of "elevated pressures".

And leading central banks continued to provide special rolling funds to open up fear-strangled interbank lending.

"We continue to bounce from boom to gloom to boom to gloom," said Richard Herring, director at Australia's Burrell Stockbroking, amid comment that the crisis is comparable to the slide towards the 1930s Great Depression.

"First and foremost this is an American crisis," Strauss-Kahn, a Frenchman and a central figure in the global economy as head of the International Monetary Fund, told the German newspaper Frankfurter Allgemeine Zeitung.

"European banks have also suffered losses ... but all in all they are in a better state that American ones. But it might be adviseable for the Europeans to prepare for the worst case scenario."

The head of the World Trade Organization Pascal Lamy issued a strong warning that the "current hurricane" hitting financial markets must not discourage efforts for greater international economic openness.

"One of the important lessons of the Great Depression, which we must not forget, is that protectionism and economic isolationism do not work," he said in Geneva.

Explaining market sentiment, Derek Halpenny at the Bank of Tokyo-Mitsubishi in London, said: "A capital injection for Goldman Sachs and the extension of dollar swap agreements between the Federal Reserve and other central banks around the world have helped calm financial markets that remain very fragile."

ABN Amro analyst Robert Lind said: "Equity markets were in the depths of despair early last week. Then there was a euphoric surge on Friday, followed by renewed gloom earlier this week."

The euro rose to 1.4663 dollars in London from 1.4657 in New York late on Tuesday. Gold dropped to 889.63 dollars an ounce from 899 dollars late Tuesday.

The New York November contract oil price rose 1.84 dollars to 108.45 dollars a barrel, but traders said sentiment was dominated by concern that the rescue plan might not save the global economy from slowing growth.

US Treasury Secretary Henry Paulson, pressing a sceptical Congress to approve his enormous plan, warned starkly Tuesday that delay carried a high risk that a racing subprime "chain reaction" would "threaten all parts of our economy."

But lawmakers remained highly critical and wary of the plan. The chairman of the Senate banking committee Christopher Dodd summed up much of the hostility in equally blunt terms: "This is not acceptable... this is not going to work."

Opinion polls suggest that the Democrats' candidate for the presidency Barack Obama has gained ground over his Republican rival John McCain on deep controversy over the crisis and the plan.

There is widespread incomprehension and outrage at how the subprime home-loan crisis developed, spreading into a global crisis, while some bankers in the field were earning huge bonuses.

US media reports said that the Federal Bureau of Investigation was looking into allegations of fraud by 26 Wall Street firms, including several of the names at the eye of the storm including Lehman Brothers, Fannie Mae, Freddie Mac and insurer AIG.

FBI spokesman Richard Kolko told ABC television the bureau "currently has 26 pending corporate fraud investigations involving subprime lenders."

The Paulson rescue was in preparation for months, it has emerged, as name after name on Wall Street hit distress, had to be rescued or headed for failure.

In Hong Kong Wednesday, hundreds of savers mobbed branches of the Bank of East Asia to withdraw deposits despite reassurances by the bank that it was not over-exposed to failed US bank Lehman Brothers and the rescued US insurer AIG.

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