Mr. Obama and many lawmakers have expressed anger that banks that received the first batch of aid money do not appear to have increased their lending significantly, even as some firms have spent billions on bonuses, corporate jets and other perks. In two weeks the House will hold a hearing to ask chief executives of the eight largest banks about their spending controls.

As early as this week, the Treasury Department may impose new limits on the executive pay of companies receiving financial assistance. The Oversight Panel created by Congress to monitor the program is also expected to publish a report this week looking at whether the government paid too much to the large banks that they have provided with assistance.

A frequent refrain in Washington and on Wall Street is that there are no current market prices for toxic securities. But people who buy and sell these investments say that is a simplistic reading of the problem. They say most kinds of securities can be valued and are being traded, but trading has slowed as sellers and buyers disagree about what that the price should be.

The value of these securities is based on the future cash flow they provide to investors. To determine that, traders have to make assumptions about the housing market and the economy: How high will the unemployment rate go in the coming years? How many borrowers will default? What will homes be worth?

The Standard & Poor’s group, Market, Credit and Risk Strategies, which operates independently from the company’s credit ratings business, has been studying troubled securities for investors and banks. The bond that is trading at 38 cents provides a vivid illustration of the dilemma in valuing these assets.

The bond is backed by 9,000 second mortgages used by borrowers who put down little or no money to buy homes. Nearly a quarter of the loans are delinquent, and losses on defaulted mortgages are averaging 40 percent. The security once had a top rating, triple-A.

Michael G. Thompson, a managing director at the S.& P. group, says his computer models can easily calculate what the bond is worth under different situations. “This is not rocket science, this is straight bond math,” he said. But determining what the future holds is much harder. “We are not masters of the universe who can predict the macroeconomic environment,” he added