Wall Street gave the new U.S. bank rescue plan an enthusiastic embrace March 23. Whether it will actually work — restoring solvency to U.S. banks, restarting lending and ultimately lifting the economy out of recession — is far less clear.

One big question is a conundrum that stumped the last administration: How to determine a price for the thicket of mortgage-related securities so banks can move them off their books, and then ramp up lending to consumers and businesses.

And even more critical to investors: Will the boiling anger over Wall Street bailouts and bonuses lead Congress to impose harsh restrictions on would-be buyers of toxic assets, making them shy away from doing a deal?

The program unveiled March 23 by Treasury Secretary Timothy Geithner aims to entice investors to buy up to a half-trillion dollars of bad assets, to shore up banks' capital and unlock credit. The program could later be expanded to $1 trillion.

Wall Street responded with its best day of 2009, sending the Dow Jones industrial average soaring almost 500 points, a rally of almost 7 percent.

Some investors are more leery. They first want to see guarantees from Congress, well attuned to the epic backlash against bonuses paid out at bailed-out financial firms, that it won't punish investors who buy bank assets and later turn a profit.

"There's a lot of fingers flying around and I'm very worried about having a high profile right now," said Steven Persky, a Los Angeles hedge fund manager who has already invested $400 billion in toxic mortgage-backed securities.