Wall Street likes President Obama’s plan for selling “toxic” assets, but key details are left unaddressed. The big one: What’s all this stuff worth, anyway?

Wall Street gave the new bank rescue plan an enthusiastic embrace. Whether it will actually work – restoring solvency to the 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 new program unveiled this week 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.

Among the investors who endorsed it was Bill Gross, a respected bond manager and founder of the Pimco investment firm. Gross said Pimco, which has more than $840 billion in client assets, would start buying troubled assets possibly within 45 days.

Another well-known investor, billionaire Wilbur Ross Jr., a specialist in distressed assets, said he plans to invest $1 billion in the plan. He said it would help banks earn the “maximum rational price” for their hard-to-value assets.

“It’s a better way than to keep pumping equity in,” Ross told The Associated Press.

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

Other 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.

Before investing any new money in toxic assets with government help, Persky said he’d want an ironclad contract guaranteeing that his profits or compensation wouldn’t be threatened later. He added: “The level of animosity is so high.”

So are the stakes.

The Bush administration abandoned its own toxic-asset purchase plan last fall because of the complexity of valuing the securities. It had proposed creating a reverse auction in which banks burdened with bad loans would accept the lowest-price bids for the assets.

By contrast, the Obama administration will try to lure hedge funds, private equity firms and other big investors to buy assets by offering them low-interest loans drawn from the $700 billion financial bailout and backed by the Federal Deposit Insurance Corp. and the Federal Reserve.

The new plan leaves it up to investors to figure out a price. The value of banks’ mortgage-related securities imploded last year after the housing crisis worsened and foreclosures soared.

The government’s goal is to get investors to pay a price at a financial sweet spot: high enough that banks will sell – but low enough that the government won’t absorb too much risk in financing the deals.

But the new plan offers few specifics on how that will be done.

“The original plan foundered on the issue of how to price the assets, and this new plan doesn’t fundamentally solve that problem,” said William Poole, former head of the Federal Reserve Bank of St. Louis. “Pricing these assets is still going to be very complicated.”

That’s because not all toxic assets were created equal. Some are simply home loans offered by banks that have since soured as people fell behind on their mortgage bills. The more pernicious assets are those backed by home loans that were chopped up and packaged into securities and sold to investors across the globe.

Putting a value on those securities means going through each one and figuring out the status of the loan. That process will be time consuming and expensive, experts say.

Eugene Ludwig, a former comptroller of the currency, said it was crucial that the Treasury Department establish the private sector partnerships quickly “so this thing doesn’t drag on for another six months.”

Ludwig, now chief executive of Promontory Financial Group, noted that the $700 billion bailout fund is mostly exhausted, meaning that the Treasury and Federal Reserve must make best use of the remaining money and whatever private money they attract.

“It’s like Hamburger Helper,” he said. “It’s a way to stretch the hamburger as much as possible.”

But success in attracting that private cash will depend on soothing investors who have been spooked by the uproar over AIG’s bonuses and other government interventions they see as heavy-handed.

Bill Seidman, a former regulator who ran the government bailout during the savings and loan crisis, said Congress’ perceived anti-Wall Street sentiment will “almost certainly keep some investors out” of the plan.

Investors “are going to want assurances” that their money will be safe, Seidman said.

Addressing those concerns in a TV interview, Geithner vowed to work with Congress to do what’s necessary to make sure investors step forward and buy the banks’ bad assets.

“For us to get the economy back on track, we’re going to need investors to take risks,” he said.

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