The nation's largest savings and loan association dropped its prime mortgage rate 4 3/4 points to 12 3/4 percent yesterday, but local lenders said they expect the decline in mortgage rates in this area to be more gradual.

The rate at Home Savings & Loan Association of Los Angeles had been 17 1/2 percent, which is generally higher than mortgage rates in the Washington area.

"We're not responding to it at this time," said Thomas W. Owen Jr., president of Perpetual Federal, the area's largest savings and loan. Owen said he expected Perpetual would study the move next week. Perpetual's rates are at about 15 percent.

"I think we're going to see a gradual decrease in mortgage rates, but how low it's going to go is questionable," said Edgar Peterson, president of National Permanent Savings and Loan. "I don't anticipate any drop in interest rates of over 4 points at one time," he said. Rates at National Permanent are also at about 15 percent.

"If savings flows reverse and we start to get a positive inflow of funds, we would be aggressive in marketing," said Eugene Dunn, executive vice president of First Federal of Arlington, where rates are about 14 percent. Dunn said savings deposit had begun to pick up in the last 10 days. "But we can't tell yet whether it's a trend or a little shot in the arm," he said.