Dodd worked with Sen. Blanche Lincoln, D-Ark., on the measure, including the swaps ban, which ranks among the top hang-ups that could threaten final passage for the overall Wall Street reform bill.
Progress on the bill has been slow going, and the Senate will continue debating amendments at least through early next week, Dodd said Thursday.
The Fed chair's concerns about the swaps ban are similar to those raised by other high profile regulators -- former Fed chairman Paul Volcker and Federal Deposit Insurance Corp. Chairman Sheila Bair. They all stopped short of blasting the measure.
0:00/4:23Buffett's stance on derivativesThe tough crackdown in question is the brainchild of Sen. Lincoln, who is facing a contentious Democratic primary in Arkansas on Tuesday in her bid for re-election. The Senate isn't expected to propose changes to the measure until after Tuesday, congressional aides and lobbyists say.
Congress generally wants to get tougher on derivatives, which are currently traded with no oversight and were a key reason for the taxpayer bailout of American International Group (AIG, Fortune 500). But lawmakers disagree about how much to regulate them.
The measure banning bank swaps goes farther than the so-called Volcker rule, named for the former Fed chief, that would only block some banks from doing such trades for their own purposes and accounts, called "proprietary trading."
The Lincoln proposal blocks banks from all derivatives if the banks want access to cheap emergency loans that the Federal Reserve can make as lender of last resort.
Bernanke said in the letter that banks use derivatives to shed risk that can arise in deals they make over interest rates, currency and other credit risks.
Senate's Wall Street bill in home stretch"Use of derivatives by depository institutions to mitigate risks in the banking business also provides important protection to the deposit insurance fund and taxpayers as well as to the financial system more broadly," Bernanke wrote.
A House bill that passed in December would allow all banks to trade derivatives in a more transparent way. However that bill also allows some trades between some banks and certain companies, such as airlines, to continue without regulation.
But Senate Democrats are tougher on derivatives, in the aftermath of fraud charges that the Securities and Exchange Commission levied against Goldman Sachs (GS, Fortune 500) for selling a complex mortgage-related derivative to investors while failing to tell them that a hedge fund was betting against the product.
When asked about negotiations on the derivatives piece on Thursday, Dodd said he understood that discussions were ongoing, but he wasn't involved in them.
FDIC chief: Bill to limit risky trades goes too farMassachusetts investigation targets banks
