The Federal Home Loan Bank Board took the country one step closer to full interstate banking yesterday by giving savings and loan associations broad new power to jump state lines and by relaxing branching restrictions on S&Ls in the District.

The bank board, which regulates S&Ls, gave federally chartered institutions the right to cross state lines if their home state gives that right to state-chartered thrifts. Today, 12 states give state-chartered institutions that right.

The rule also gives the bank board additional authority to entice healthy thrifts to purchase ailing ones. The bank board could allow federally chartered thrifts that buy an ailing S&L to expand into as many as three additional states in the region where the ailing thrift is located. Until now, S&Ls acquiring sick thrifts were permitted to expand into only one additional state.

The bank board also passed a long-awaited ruling allowing S&Ls in the District to branch into either Maryland or Virginia, but not both, and to allow S&Ls in the two states to open branches in the District.

The ruling does not change the status of local S&Ls, such as Perpetual American Bank of Alexandria, which, through the purchase of ailing thrifts, already has offices in the District and Maryland, bank board officials said.

But, it will permit Columbia First Savings & Loan, a D.C. thrift with assets of $1.3 billion and offices in Virginia, to expand into Maryland.

It also will allow Meritor Savings Bank of Arlington, which has assets of $900 million and offices in the District, to expand into Maryland. "We're delighted with the new opportunity," said Meritor spokesman John McRorie. "About 40 percent of our customers reside in Maryland, and this gives us a way to serve them better."

Analysts and thrift-industry executives hailed the new rules as raising the value of healthy and unhealthy institutions alike. The relaxation of interstate branching rules will enable healthy institutions to compete in wider market areas, they said.

Perhaps more important, analysts said, the bank board has found a way to raise the value of troubled thrifts, such as National Permanent Bank, the District's largest thrift institution, without the use of controversial accounting techniques.

The new interstate rule governing the acquisition of ailing thrifts gives the bank board a bigger bargaining chip as it seeks solutions to 461 troubled institutions across the country. Selling an institution costs the Federal Savings and Loan Insurance Corp. -- the bank board division that insures deposits up to $100,000 -- much less than liquidating a thrift.

"The bank board will be able to move bad S&Ls much more quickly," said Emanuel Friedman, S&L analyst for Johnston, Lemon & Co. of the District. "It's a very dramatic change."

"No one really wants a bad S&L," he said. "What they want is the right to buy healthy ones in new markets. That's what they're really buying. The [rule] change increases the competitiveness of every good S&L in the country."

Bank board officials agreed that giant companies from a variety of industries may be able to benefit from the new rules, even though additional regulatory approval may be needed. Citicorp, Sears, Roebuck & Co. and Ford Motor Co. all own thrift institutions, for example.

But bank board officials played down the significance of allowing healthy thrifts buying an ailing institution to leap into several new states.

The ruling on D.C. institutions takes effect 30 days after the rule is published in the Federal Register. The national interstate rule will take effect as soon as it is published. Both rules could be published as early as Monday.