WASHINGTON — Irked that Goldman Sachs appears to have reaped a $2.9 billion taxpayer-aided windfall on an investment of a mere $20 million, some experts and watchdogs say the Wall Street giant should return the money to the U.S. Treasury.

"This wasn't rocket science, what was going on," said Michael Greenberger, a University of Maryland law professor who specializes in complex securities. "Anybody who understood this market knew that there was the potential for Goldman to later unwind proprietary trades. But the Obama administration and the Fed simply never inquired." "It's a very simple call to make," said Sylvain Raynes, a frequent Goldman critic who's an expert in the kinds of deals in which the investment bank landed an apparent jackpot. "They should never have been given this money, and they should give it back."

The assessment by the Financial Crisis Inquiry Commission also exposed a potentially huge regulatory omission in the rescue of the insurance giant American International Group, which was the conduit for more than $90 billion in tax dollars to U.S. and European banks.

It's now clear that the Federal Reserve Bank of New York, which quarterbacked the hurried, $182 billion bailout of AIG to avoid a meltdown of global financial markets, did little to guard against windfalls for major banks and investment banks.

The financial crisis panel's final report late last month found that Goldman's $2.9 billion payout came on "proprietary" trades — investments in which the firm used its own money rather than the more typical deals completed on behalf of clients.

The panel, inquiring into a McClatchy report last June, said that Goldman got $1.9 billion of the payoff after the taxpayer bailout of AIG began.

Critics say that in the rush to save AIG and avert systemic collapse of the financial markets, regulators treated Goldman like everyone else. But Goldman was different.

While most banks that got billions of dollars from AIG simply relayed the money to clients they'd insured against losses, Goldman got to collect a more than 100-fold return on a number of securities that soured, because none of its clients was involved.

The prospect of a repayment by Goldman — the firm that drew the most outrage over Wall Street's role in the financial crisis — would be welcome news now as President Barack Obama has been forced to propose huge cuts in federal programs as a way of dealing with a $1.6 trillion budget deficit for fiscal 2012.

Steve Ellis, of the government waste watchdog Taxpayers for Common Sense, said that "It's up to the federal government to demand accountability and transparency" regarding Goldman's payout.

"We can't afford to shell out cash without asking hard questions and demanding that the very same actors that got the economy into this mess take some of the burden on themselves," he said.

Congress could try to impose a tax on banks' profits from the bailout or adopt some other legislation to "claw back" the money, but it would be difficult because Goldman received it unconditionally, said Michael Greenberger, a University of Maryland law professor who specializes in complex securities. The New York Fed attached no strings to the money and let AIG decide how much Goldman would get.

Goldman, which paid a whopping $31.6 billion in employee bonuses in the past two years, denies that the trades in question were proprietary, signaling that it has no plans to send more money back to Washington.

In 2009, Goldman was quick to repay a $10 billion loan from a Treasury Department program to bail out banks. Last summer, the firm paid an additional $550 million to settle a related civil fraud suit filed by the Securities and Exchange Commission.

Goldman spokesman Michael DuVally rejected the characterization of the AIG payment as a windfall.

"We used the money we received from AIG to meet our obligations to clients with whom we hedged on the other side of these trades," he said.

Joseph Mason, a finance professor at Louisiana State University-Baton Rouge who has advised federal banking regulatory agencies, said that most large banks manage their risks with so many contrary trades that assertions they profited from a particular deal "can be obviated very quickly."

The issue, however, goes to the heart of the controversy over whether any of the megabanks that helped cause the crisis got sweetheart deals as part of the bailout.

"In the heat of the moment, the Treasury and the Fed weren't worried about who was participating in the housing bubble . . . or their level of involvement" when they shelled out money, Mason said.

"You run up the market, you cause a nationwide crisis and you're given money to continue. That sounds to me like an incentive to go out and do it again."

The New York Fed said in a statement that the bailout protected Americans, as well as AIG's policyholders and trading partners "from the catastrophic consequences of AIG's disorderly failure during the worst financial crisis in generations, (and) allowed AIG to meet its contractual obligations without discrimination." A New York Fed spokesman declined to comment on whether taxpayers backstopped any other proprietary trades

Greenberger, however, sharply criticized the handling of the AIG bailout, naming Federal Reserve Chairman Ben Bernanke; Treasury Secretary Timothy Geithner, the former New York Fed president; and Larry Summers, until recently Obama's chief economic adviser.

"This wasn't rocket science, what was going on," said Greenberger, who was a senior staffer at the Commodity Futures Trading Commission during the Clinton administration. "Anybody who understood this market knew that there was the potential for Goldman to later unwind proprietary trades. But the Obama administration and the Fed simply never inquired.

"They had all the power at that point. Goldman needed that money. They were on their knees, and that was the point at which hard bargaining should have been taking place."

However, Greenberger said he worries less about recovering taxpayer money than about preventing a future financial meltdown, because the banking industry is lobbying fiercely against rules implementing recent congressional overhauls by improving market transparency and limiting risk-taking.

AIG's big debts to Wall Street emanated from the decision of its highflying London-based Financial Products unit to write insurance-like protection for major banks and investment banks on some $78 billion in offshore securities, most backed by subprime or similarly dicey home loans. In many cases, the banks had written identical insurance protection for the buyers of the securities.

When the housing crash sank the securities' value, AIG was sent reeling toward bankruptcy by a chorus of banks demanding payment of tens of billions of dollars under the terms of the contracts, known as credit-default swaps.

Geithner, Treasury secretary Henry Paulson and Ben Bernanke elected to save AIG from bankruptcy, partly to keep banks afloat. As part of the rescue, the New York Fed directed AIG to cover the full face value of $62 billion of most of its swap contracts with Goldman and other U.S. and European banks.

Goldman, which collected $14 billion of those funds, said it merely forwarded the money to investors for whom it had written the same protection.

But the inquiry panel concluded that Goldman cashed in on another $5 billion in more exotic bets on so-called synthetic securities that weren't back-to-back trades. With AIG Financial Products unworried about a housing downturn, Goldman paid 0.1 percent of the securities' face value, or about $5 million annually, to bet in 2005 and 2006 on the default of a set of securities that neither party owned.

DuVally, the Goldman spokesman, said that the deals "were client-related, not proprietary transactions," emphasizing that, "The idea that we received a . . . windfall is wrong."

DuVally declined to detail the hedges — bets in the opposite direction — and wouldn't say whether Goldman had anything close to $2.9 billion at stake.

Another $1 billion in Goldman-AIG trades had yet to be unwound as of July.

It's still unclear whether other banks also collected windfalls for proprietary bets.

The French colossus Societe Generale, investment bank Merrill Lynch (now owned by Bank of America) and Germany's Deutsche Bank collected a combined $22 billion from AIG as part of the 2008 settlements. Deutsche Bank also insured billions of dollars in securities backed by commercial real-estate loans.

Spokesmen for AIG and all three banks declined to comment.