WASHINGTON — Leading members of Congress on Friday demanded that federal regulators strengthen proposed banking rules and scrutinize trading closely in the wake of JPMorgan Chase’s disclosures of trading losses.

“The fact that this can happen at a bank with a solid reputation like JPMorgan is evidence that our banking regulators must remain vigilant,” said Senator Tim Johnson, the South Dakota Democrat who is chairman of the Senate Banking Committee, “and why opponents of Wall Street reform must not be allowed to gut important protections for the financial system and taxpayers.” The bank has been a leader of industry lobbying against new strictures on trading practices.

The chairwoman of the Securities and Exchange Commission, Mary L. Schapiro, said the agency was focused on JPMorgan Chase’s newly disclosed trading losses, and other people with knowledge of the agency’s activities said it was already examining possible civil violations involving the bank’s public statements and disclosures.

Two Senate authors of the law restricting certain kinds of high-risk trading by banks blasted federal regulators, saying that the agency’s draft regulations would not adequately address trading of the kind that has now cost JPMorgan Chase enormous losses.