The prime rate, which peaked at 21.5 percent in December 1980, is less than half that today. Mortgage rates have dropped to their lowest level in almost five years. The interest rate on some dealer auto loans is now in the single digits.

At the same time, department stores still charge 21 percent-plus on revolving credit. Unpaid balances on credit cards require 18 to 19 percent annual interest payments. And personal loans for walk-in customers generally remain unchanged at 18 percent annual interest.

"Commercial borrowers have benefitted more from a decrease in the prime than have consumers," Rep. Barney Frank (D-Mass.) said recently.

Robert Heady, publisher of Bank Rate Monitor in West Palm Beach, Fla., which tracks interest rates, reports no significant downward trend, considering the way rates are dropping on deposits. He observed that some lenders are trying to make up for the tight squeeze last January when they had to pay higher rates on deposits.

With the exception of residential mortgage loans, automobile loans and some lines of credit tied to the prime rate, consumer loan rates have yet to show any significant decline. This is true in the Washington area as elsewhere.

A telephone survey of a dozen credit providers conducted over the past three weeks revealed that the interest rate on the unpaid balance of revolving charge accounts at leading retailers remains at an all-time high. Woodward & Lothrop bills at 21.8 percent, Hecht's at 21.6 percent and Sears Roebuck at 21 percent. A Sears spokesman said there were no current plans to reduce the rate. The local merchants declined to comment.

One reason for the continued high rates is the relatively high administrative cost of financing small loans. For example, Sears' average credit balance is $472.

Craig Ulrich, an attorney for the Consumer Bankers Association, suggests another deterrent is the paperwork involved in notifying customers of a change in rates as required by law. Still other reasons cited for the continued high rates include the lack of competition among stores, customer apathy -- few shoppers would make a purchase based on the revolving charge rate -- and, of course, profit at a time when retail sales are stagnant. May sales actually declined slightly from April.

Virtually unchanged are rates prevalent on bank cards. Citicorp, for example, retains 21 percent on its Choice card, 19.8 percent on MasterCard and 19.8 percent on the line of credit attached to the preferred Visa card. A spokeswoman for American Express said the vast majority of the banks offering a line of credit on its Gold Card charge 18 percent annual interest.

A few institutions tie the credit line to the prime rate. Chevy Chase Savings and Loan has begun to offer regular and premium cards at 4.5 percent over prime. As of last week, Sovran Bank, which was charging 12.5 percent before April, charged 12 percent and will reduce the rate to 11.5 percent on July 1. A spokesman said Sovran can offer that rate by holding expenses down -- there has been no advertising campaign -- and maintaining very high credit standards. He added, "None of our competitors has made a major effort to undercut us."

Credit grantors, remembering how they were burned when market rates rose and they were unable to raise their rates, are reluctant to lower them now. Robert Gibson of the National Foundation for Consumer Credit, a nonprofit credit counseling center, said he sees no prospect of a reduction for the foreseeable future.

"Retailers must be convinced inflation will stay down," he said. "They are also watching tax and deficit legislation and hoping for a strong stand by the Federal Reserve."

Rates on plastic -- which often reflects impulse buying -- often, but not always, are higher than those on lines of credit accorded regular bank customers. These overdraft accounts, known by various proprietary names such as Ready Money, remain largely unchanged at 18 percent in this area, but there are some exceptions. Perpetual American Bank charges 12.5 percent; First Virginia Bank, 11.5 percent.

Unsecured loans, or personal loans without collateral, range from 15 to 18 percent in this area, with little movement. One exception is Continental Federal Savings and Loan, which cut back to 16 percent from 17.5 percent a month ago.

There has been little incentive this year for cutting rates, according to Albert E. DePrince Jr., chief domestic economist of Marine Midland Bank. Demand has remained strong until now, with total consumer installment debt up 21.3 percent over last year. However, April figures showed a gain of $8.27 billion, off a bit from the March gain of $8.34 billion. In revolving credit, which includes retail and bank card borrowing, the May increase was $2.13 billion, compared with the April increase of $2.63 billion.

Mickey D. Levy, an economist with Fidelity Bank in Philadelphia, expects credit card rates to recede, given the recent decline in the cost of funds. Allen Sinai, chief economist at Shearson Lehman Brothers Inc., expects consumers will see big reductions by the end of the year if inflation continues low and there is continued weakness in the manufacturing sector.

Citicorp, which often leads the way on retail rates, recently announced a loan sale on bank card credit. Between June 15 and Sept. 15, one-half of the charges go on the card at the old rate of 18 percent, and the other half at 12 percent. Madison National Bank advertised a home improvement "loan sale" with a promotion typical of an appliance sale. "For three hours only, on one day only," rates were reduced from the original price of 16 percent to 11.75 percent. After the sale, the rates went back up somewhat.

Vice President Francis Simmons explained that the bank is repricing its loans across the board because the market is dropping. Moreover, Madison wanted to add to its loan portfolio and chose home improvement loans as the vehicle.

The greatest movement in consumer lending appears to be in larger automobile and home equity loans. One factor is competition from dealers who have been pricing loans for hard-to-move compacts and subcompacts at 8.5 to 8.8 percent. (Loans on the more popular full-size cars remain in the 13 to 14 percent range.) Another is the increasing trend toward tying the loan rate to the prime rate. As such, several banks have dropped their rates at least one-half percentage point, and some a full percentage point, in the past month.

Car loans at the institutions surveyed ranged from a low of an 11 percent variable rate at Maryland National Bank to a high of 14 percent at First National Bank of Maryland.

Home equity loans can be made as standard second mortgages with fixed installment payments or the newer form of open-end loans without fixed payments. First American Bank, for instance, charges 14 percent on a fixed loan and prime plus 1 1/2 percent on the open-end loan. Loan amounts typically range from $10,000 to $100,000, and funds can be accessed by check whenever needed for paying college tuition or financing a vacation.

The variable-rate loan is growing in popularity, and the competition among banks appears to be greater, resulting in some promotional rates. For example, Chevy Chase Savings and Loan offers an 8.75 percent loan until September 1985 when the rate will rise to 1 1/2 percent over prime. American Security Bank has lowered its rate to 10 percent. Riggs and Maryland National reported no change in their rates, which were 12.5 and 11.5 percent respectively.

On home equity loans, there is invariably some kind of additional up-front cost, known as appraisal, loan origination or administrative fee. It is either a flat fee or a percentage and can add considerably to the true annual percentage rate for the borrower, especially if the loan amount is modest. At American Security Bank, for example, the fee ranges from $250 to $750; at Perpetual American, it is two points, or 2 percent, of the loan amount.