By Daniel Trotta and Jennifer Ablan

NEW YORK (Reuters) - For many Americans this feels like the worst economic crisis in their lifetimes, and some leading investors are starting to say they may be right.

The bursting of the dot-com bubble in 2000 and 2001 seems tame by comparison, and the savings and loan crisis of the late 1980s and early 1990s almost forgettable. Similarly, the global impact looks to be greater than that of the Asian financial crisis of 1997 and 1998.

Most comparisons turn to the low growth, high inflation, weak dollar and soaring energy prices of the 1970s, but this time with a housing crisis and spiking commodities prices thrown in, all threatening a prolonged recession.

"It is the most serious financial crisis of our lifetime," said billionaire investor George Soros, noting a growing effect on the U.S. economy as a whole, rather than just financial markets. "It is an idle dream to think that you could have this kind of crisis without the real economy being affected.

"We are facing a recession and it is slow in coming but the slower it comes, the more powerful it is," Soros told Reuters.

The rapid erosion in confidence in Freddie Mac and Fannie Mae underscores the toxic nature of the problems facing the U.S. financial system. The publicly traded, government-sponsored enterprises (GSE) own or guarantee $5 trillion of debt, close to half the value of all U.S. mortgages.

With 8,000 to 9,000 American homes entering foreclosure every day, stock in Fannie and Freddie lost nearly half their value last week, leading the U.S. Treasury to open its discount window to the two firms to ease fears over their capitalization.

This comes as U.S. stock indexes have fallen by more than 20 percent from their peaks in October, while the pan-European FTSEurofirst 300 is down 30 percent, the Shanghai Composite has dropped 45 percent since the year began and Japan's Nikkei 225 is also significantly lower.