Federal banking regulators are preparing new regulations that would open the way for hundreds of savings and loan associations to change themselves into state-chartered savings banks, according to sources at the Federal Deposit Insurance Corp.

Details of the proposal are to be presented tomorrow to the board of the FDIC, but the change is expected to further blur the distinctions among S&Ls, savings banks and commercial banks and represents one more step in what many experts believe will be the eventual consolidation of the three kinds of financial institutions.

The proposal is expected to end a moratorium on conversions of S&Ls into savings banks that was instituted by Timothy J. Ryan, director of the Office of Thrift Supervision. The OTS is responsible for oversight of savings and loan institutions.

When he halted all conversions in October, Ryan said thrifts were trying to escape restrictions on risky S&L investments that were imposed by Congress last year. The 1989 law prohibited S&Ls from investing in junk bonds and risky real estate ventures, but it did not apply to savings banks.

Congress considered legislation to ban S&L-savings bank conversions this fall, but it tabled the measure after Ryan imposed his moratorium.

The FDIC staff is recommending new regulations that would require any S&L that becomes a savings bank to continue to live by the S&L restrictions on investments, the sources said. The new rules would not apply to the 400 existing savings banks, which would continue to have greater freedom in investing depositors' money.

Savings banks are hybrid financial institutions, a cross between a bank and a savings and loan, that are chartered by 15 states, mostly in New England. Like S&Ls, savings banks concentrate on home mortgage lending, but they also have legal authority to make the same kinds of loans and investments as regular banks, known as commercial banks in industry jargon.

S&L executives say the main reason they want to become savings banks is to escape the high cost of being regulated and examined by two different federal agencies -- the OTS and the FDIC. Federal bank agencies are financed not by taxes but by special assessments imposed on financial institutions based on their size.

The FDIC examines state-chartered savings banks and its assessments are much lower than those of OTS. Executives of thrifts considering conversion estimate that it would cut their regulatory costs by two-thirds.

Another reason to become a savings bank, many thrift industry officials said, is to avoid the stigma of the S&L name, which has been tainted by the most costly scandal in the nation's history.

The expected FDIC action was hailed by thrift industry trade groups.

"This will lead a lot of people to consider converting," predicted James Grohl, spokesman for the U.S League of Savings Associations.

"This was clearly the most important thing on our members' current agenda," said Charlotte LeGates of the National Council of Savings Institutions. "We are in favor of anything that would permit S&Ls to change charters and get away from the high OTS fee."

The new rules do not affect the large number of savings and loan associations that call themselves "federal savings banks." Such institutions as Perpetual Federal Savings Bank and Chevy Chase Bank operate under S&L charters because neither Virginia nor Maryland permits savings banks.