Wall Street, trying to preserve profits from swap trading in the face of tougher scrutiny from Washington, has found a new way to keep some of its overseas deals private. It's called Footnote 513.

Banking lawyers have seized on the wording of the footnote, contained in an 84-page policy statement issued in July by the main U.S. regulator of derivatives. The largest banks told swap brokers in late September that the language means certain swaps still don't fall under the agency's new trading rules, according to three people briefed on the discussions.

London-based ICAP Plc, one of the largest swap brokers, told the banks it didn't agree with their interpretation, said the people, who spoke on condition of anonymity because the discussions weren't public. Other brokers accepted the banks' position and have been trading billions of dollars in contracts outside the new regulatory system, the people said.