Major U.S. banks lowered their prime lending rates yesterday to 11.5 percent from 12 percent in the wake of Friday's half-point cut in the Federal Reserve Board's discount rate, but these latest declines in interest rates were not enough to boost the stock market, which closed sharply down on the day.

The Dow Jones Industrial Average finished down 21.25 points at an even 1000. The list of blue chip stocks on the New York Stock Exchange has lost 65 points since reaching a record high on Nov. 3, the day after Election Day.

Chase Manhattan, the nation's third largest bank, led the prime rate move yesterday. It was quickly followed by Chemical Bank, which had raised its prime to 12 percent only last week, after several weeks as the only major bank charging 11.5 percent. The last time the prime was generally as low as 11.5 percent was in September, 1980.

Banks can afford to lower their prime because the cost of funds that they borrow in the money markets has declined. Yesterday the federal funds rate -- charged on overnight money that the banks borrow from each other -- was below 9 percent.

Although economists believe that lower interest rates should eventually help the nation to pull out of recession, the Federal Reserve's discount rate move had been widely anticipated and so was "a bit of a non-event" as far as the stock market was concerned, Elliot Platt of Aubrey Lanston said yesterday.

The cut made it clear, however, that the Fed has moved away "at least temporarily" from strict control of the money supply, Platt said. The central bank has encouraged interest rates to fall even though monetary growth has exceeded the Fed's targets, and is widely thought to have eased credit conditions at least partly because of the prolonged and deep recession. Last week it said its discount rate cut came against a background of "continued sluggishness in business activity" and progress against inflation.

Despite recent declines in interest rates, top business economists have recently become even more gloomy about the prospects for recovery next year, according to a survey released yesterday. The National Association of Business Economists (NABE) predicted growth of only 3.3 percent next year, below the 3.5 percent forecast in the August survey. Administration officials have said that 4 percent growth rate should be possible in 1983.

Meanwhile, Henry Kaufman, chief economist of Salomon Brothers, warned yesterday that while the odds were still against a repetition of the Great Depression, "the odds are shrinking."

Several economists believe that interest rates must fall still further before the economy will respond, although the NABE survey showed that nearly 80 percent of the business economists think that current monetary policy is "about right." This is a rise from earlier this year, before the Fed began to ease credit conditions.

The Fed has moved gradually in reducing its discount rate -- the rate charged to financial institutions that borrow from the Fed -- bringing it down in steps of one-half point at a time. It probably will not lower it again until at least the end of next month, after the next meeting of the Fed's policy-making Federal Open Market Committee, analysts said yesterday.

While the cut in the discount rate helped to bring other market interest rates down yesterday, consumer loan rates remain very high. Credit card interest rates range from 18 percent to 21 percent, and many have recently been raised. These rates may affect consumer willingness to spend during the coming Christmas season, analysts say.

Retailers have so far been somewhat pessimistic about the prospects for Christmas sales, and recent economic indicators have not done much to relieve that gloom. Employment and production shrank further during October, recent government figures say, although there has been some sign of improvement in the housing and auto markets. These are both highly sensitive to the level of interest rates.

The prime rate is supposed to be the rate which banks charge to their best customers. However, many large corporations negotiate loans with banks at below prime. Smaller and medium-sized businesses are more directly affected by changes in the prime.