The higher interest-rate ceilings on savings accounts announced this week by federal regulators represent an effort to compromise between depository institutions competing for the shrinking dollar. The result, said one economist, is as complicated as Rube Goldberg contraption.

The regulators set an effective floor of 9.5 percent on 30-month small-saver certificates sold by savings and loan associations and 9.25 percent on those sold by banks. This means that even if the interest rates on 30-month Treasury securities go lower, the rates on these certificates won't. The ceiling was left at 12 percent for thrifts, 11.75 percent for banks.

More stringent penalties for premature withdrawal were authorized. for the first time, a depositor stands to lose part of his or her principal, as well as interest, by withdrawing the money early.

The changes in the six-month money market certificate mean investors will get one-quarter percentage point more than the discount rate on Treasury bills. A savings and loan can offer one-quarter percentage point more interest than banks only when the interest rate on the underlying Treasury bill is between 7.25 and 8.78 percent. Above or below those figures, both institutions may pay the same rate on new money market certificates.

An exception is made for maturing six-month certificates that are rolled over at the same institution. In this case, banks will pay as much as S&Ls regardless of the underlying Treasury bill rate. This move is designed dissuade customers from switching their funds from banks to savings and loans.

This is the second controversial decision taken by the Depository Institutions Deregulation Committee since its creation by Congress a couple of months ago. The first -- which may be abandoned -- was to bar institutions from offering gift premiums for new deposits and bringing in new customers.

DIDC is made up of the six financial chief of the U.S. Treasury, the Comptroller of the Currency, the Federal Reserve, the Federal Deposit Insurance Corp., the Federal Home Loan Bank Board and the National Credit Union Administration. The banks, which are pressing for a rapid phase-out of the one-quarter percentage point differential enjoyed for many year by thrift institutions, have a numerical advantage on this committee.

According to those present at the committee's deliberations -- the policy-forming sessions were closed to the press -- the thrifts' regulator fought hard to save the differential but lost. (When the quarter-point advantage for certificates paying over 9 percent was lifted last year, S&Ls saw their share of the MMC market fall from 54 to 41 percent. while the banks' share rose from 30 percent to 47 percent.)

As a compromise, the committee voted to take away the differential on all except a narrow range of six-month certificates but to allow both banks and thrifts to pay one-quarter percentage point more on these certificates and one-half point more on 30-month certificates than the underlying Treasury bill rate would have justified. The result is a plus for the investing public, although a headache to calculate.

The U.S. Savings and Loan League immediately cried out that the decision represented "a major new defeat for housing" because it favored commercial banks over thrifts. Generally speaking, the interests of small banks that lend to small business and farmers are thought to have won out.

Like previous rate actions, the move also was designed to make a dent in the growth of money market funds. Historically speaking, the commercial paper, large certificates of deposit and bankers acceptances that constitute the bulk of the funds' portfolios tend to have higher yields during a recession as people put their money into safer investments like Treasury bills. Although this hasn't yet happened, the financial regulators are trying to blunt the effect of expected higher MMF yields by making money market certificates more attractive.

David Silver, president of the Investment Company Institute, the trade association for mutual funds, said yesterday he didn't think the small upward movement in MMC rates would have any effect on money market fund growth. (These funds are now yielding over 12 percent; the new "clone" funds are yielding over 10 percent.)

Neither is the move expected to hurt sales of Treasury securities, although it breaks precedent by undercutting the government's own securities. If interest rates continue to plunge, money market certificates -- based on Treasury bill rates -- will become better buys than the bills themselves.

Some individual investors may be dissuaded from buying Treasury bills, an economist said, but the large institutions are likely to prefer the liquidity of Treasury securities rather than subjecting themselves to premature withdrawal penalties by buying MMCs.

But, added the economist, the committee may change its mind again if Treasury bill rates go too low. And he said he, for one, would breathe a sigh of relief when this Rube Goldberg regulation is dismantled.