WASHINGTON—Jamie Dimon got right to the heart of Congress's concern yesterday when he told a Senate Banking Committee hearing that his bank, J.P. Morgan Chase, "did not cherry pick the assets in the collateral pool."

He fielded—as did others testifying in the banking committee's crowded, but cold and cavernous hearing room—repeated questions from senators trying to delve into the details of the collateral the federal government received for helping the emergency takeover of Bear Stearns - and just how that was valued.

Unsurprisingly, there were a lot of defensive statements by both bankers and federal regulators who insisted they were bailing out the American economy, not just one financial institution. But no specific details—let alone an actual price tag—of just what the federal government got for sticking its neck out  were disclosed during the five plus hours of testimony.

Dimon, who noted that J.P. Morgan was taking on  $300 billion of Bear Stearns debt, testified that the "process of designating what collateral would be pledged was overseen by the New York Fed's adviser, BlackRock, a recognized expert in the field."

He warned, however, that "no one can predict how that portfolio will ultimately perform—and, of course, it could actually increase in value—if the portfolio declines in value, the first $1 billion of that loss will be borne solely by J.P. Morgan."

Under questioning, Dimon said there was a confidentiality agreement with the Federal Reserve preventing him from disclosing any more, but noted that the collateral was "investment grade." When Robert Menendez, Democrat of New Jersey, tried to zero in further on the contents of the government's newly acquired portfolio, Dimon said that the collateral was not the risky mortgage-backed securities and hedge fund assets, and that it was Bear Stearns' valuation —backed by BlackRock— that established its value.

"Why did Bear fall on a series of rumors if it was not a question of valuation at the end of the day?" Menendez said.

Earlier, Ben Bernanke, the Federal Reserve chairman, insisted that American taxpayers' risk was "not remotely close" to the $29 billion ($30 billion minus the $1 billion J.P. Morgan took on), and most, if not all, of it would be recouped when the investments were sold - which can happen over a period of 10 years.

Dimon and Bear's chief executive, Alan Schwartz, gave their testimony after waiting out four hours of senatorial grilling of Bernanke and others. A full complement of Senate banking committee members were on hand to hear the first extended explanation of how Bear went from a top Wall Street investment firm to near-collapse in a matter of a few days.

Timothy Geithner, president of the Federal Reserve Bank of New York, described the round-the-clock negotiations to save Bear Stearns from what those testifying frequently called a "run on the bank."

A chastened Schwartz insisted that Bear had strong liquidity that met required guidelines, but said it was felled by an avalanche of unsubstantiated rumors that thoroughly undermined market confidence.

Senators pressed Christopher Cox, chairman of the Securities and Exchange Commission, to say whether investigators were looking into whether the rumors were from sellers shorting the stock. Bear stock plummeted from about  $60 to $5 within a few days in mid-March—and the amount of trading soared.

Cox said he was constrained from disclosing investigations and potential litigation, but  but about the third time he was asked, he hinted that the enforcement division was busy looking into exactly what took place in the lead-up to the Bear Stearns mess.