Recent changes in the legal limits on credit card finance charges have produced a bevy of new and increased interest rates and left confused consumers scrambling to find the best deal on credit cards.

Interest rates on credit card balances now vary from 12 to 21 percent and the range of costs grows even greater when you add in such other items as late penalties, origination fee or annual membership.

A cardholder's financial habits are another part of the equation. An annual membership fee will raise the true cost more for the person who pays for charges every month and rarely incurs a finance charge than for one who regularly pays the minimum rather than full amount due.

A requirement that the cardholder maintain a low-interest checking or savings account with the issuing bank can make more difference in dollars than the absence of costs like late penalties.

As of now, the District of Columbia continues to have the most advantageous terms for customers: an 18 percent interest ceiling and no annual fee. But few banks are interested in providing service under these rules. Starting next April, Virginia will have potentially the least advantageous terms of the three jurisdictions: no interest rate ceiling and fees permitted. Maryland falls in the middle: a 24 percent ceiling, but no fees. However, many Maryland customers will come instead under Delaware's terms--which are similar to Virginia's--because big Maryland issuers have moved to Delaware.

In the country as a whole, the number of states that allow banks to charge fees outnumber those that don't by 27 to 16, according to The Nilson Report, a Santa Monica-based newsletter for industry executives. (Eight states put a limit on the fee amount.) A dozen states have no interest rate ceiling for credit card purchases or they allow a floating rate. Only five--California, Delaware, Nevada, New York, and South Dakota--place no limits on rates or fees, while 19 have restrictions on both.

A Washington Post survey of credit card issuers in the area reveals a considerable variation in terms in this transition period. Rates will undoubtedly become more homogenous later on. District results reflect little change since the law was amended last March to permit a flat 18 percent interest rate on the entire balance. The Virginia terms given in the accompanying chart will be maintained until next April. The Maryland terms represent those now in effect.

However, most of the banks that have kept their operations in Maryland indicate they are contemplating a rise in rates by next fall. Although they were legally able to raise rates on July 1, with one exception tbey have not done so. Competition--waiting to see what the other guy is going to do--is one reason. But the main cause of delay is the need to program computers to carry old balances at the lower rate until they are paid off and simultaneously carry new purchases at the higher rate.

Banks and other financial institutions that issue credit cards are listed in the chart accompanying this article; agents for banks elsewhere are not, except as noted. Of the 21 questions asked in the survey, the eight on which there was the most variaton are shown on the chart. There were, for example, almost no exceptions to the custom of allowing between 25 and 30 days before finance charges are imposed on purchases of goods and services, but no free period for cash advances. Some credit unions do not offer a grace period on either type of credit.

All issuers surveyed used the average daily balance method of computing finance charges. When a new purchase is made and added to an outstanding balance, finance charges are sometimes levied on the entire amount. In other words, there is no grace period for the new purchase. In Maryland, about half the issuers use this method. Half do not add finance charges to the new purchase right away. In Virginia, the second method is more common among those surveyed.

Credit limits are hard to determine due to different scoring systems used, the impossibility of quantifying human judgment, and a general reluctance of issuers to discuss the subject for proprietary reasons and for fear of encouraging fraud. Some credit unions have absolute maximums; most banks don't. All issuers maintain that credit limits are determined by the customer's ability to pay. The figures on the accompanying chart are meant just to give a rule of thumb. Many issuers automatically do not renew a card if there is no activity for a year or 18 months.

Of the three jurisdictions, Maryland has the most fluid situation.

Although banks in that state were given the power as of July 1 to raise interest rates to 24 percent (over the previous rate of 18 percent on the first $700 and 12 percent thereafter), they were not allowed to charge annual fees.

The issue of fees remains controversial. Approximately half of all cardholders pay their bills in full each month. The issuer does not make any money on these convenience users; instead, it costs the bank money to send out statements and to advance them money for a month. Why should cardholders who incur finance charges also have to pay for those who don't, banks ask. Yet experiments in other parts of the country with transaction fees, reflecting actual use, have proved less popular with customers than fixed annual fees.

Because of Maryland's restrictions, four of the largest banks in that state have announced or completed moves of their credit card operations to Delaware. They are Equitable Trust (whose Delaware operations are known as Equitable Bank of Delaware), Suburban Bank, Maryland National Bank (Maryland Bank NA), and First National Bank of Maryland (First Omni). A spokesman for Citizens Bank and Trust had no comment when asked if its credit card division was leaving the state.

The moves have provoked some Marylanders. A spokesman for Maryland Bank NA, which moved in March, said there has been a small number of card cancellations, but it will be some time before the bank can tell how many persons intend to stop using their cards. On the other hand, Union Trust, which is staying in Maryland, said card applications have doubled since March. The Savings Bank of Baltimore, also staying, reported it was "innundated" with 10,000 applications in the last three months, "99 percent of them from people who are more upset at the moves than at the annual fees," said vice president Jeff Brown.

It is in Maryland that the highest and lowest annual percentage rates are found at the moment. Citicorp's Choice card now carries 21 percent financing in that state. By contrast, Guardian Federal Savings and Loan still charges existing customers 12 percent. However, it is not accepting any new accounts, and the low rate appears likely to vanish. Citizens is not accepting new customers, either.

When the prime rate soared in 1980, District bankers lobbied hard to get the interest rate ceiling raised above 20 percent--a level at which credit card operations would become profitable, they said. The City Council agreed on the rise for installment loans, but permitted only a slight change in credit card rates. The 18 percent rate on the first $500 charged and 12 percent on the remainder jumped to 18 percent on all outstanding balances.

The Central Charge card, which Riggs National Bank has issued for many years, is still being offered at the old split rate. Officials said a rate increase is now under evaluation. Apart from Central Charge, there is still no interest among District banks in issuing bank cards, according to D.C. Bankers Association President C. Jackson Ritchie. But he insisted that "the credit card question isn't dead in D.C." Some banks act as agents for out-of-state issuers and seven D.C. financial institutions have recently begun to issue the hybrid American Express Gold Card.

Virginia's usury ceiling will be lifted next spring. Bankers there contend that elimination will not automatically mean customers will pay higher rates. They argue that the flexibility gained will attract more issuers and competition will keep rates in check.

(Several Cleveland, Ohio, banks recently began imposing variable rate finance charges as the fairest solution to fluctuating interest rates, but no local issuers have yet elected to do so.)

First American is the only bank not requiring an annual fee among Virginia banks surveyed, but that policy will be reviewed next year, said a bank official. Citicorp does not charge a fee on its Choice card, nor do any of the federal credit unions in Virginia and elsewhere charge fees.

Of the four credit unions surveyed, three are relative newcomers to the credit card industry. They say their terms may be revised as they gain experience. For now the non-profit organizations can charge lower interest rates than banks because their expenses are lower, their risk is lower with proven member-customers, and they begin imposing finance charges from the billing date.

As terms become more flexible, out-of-state issuers have stepped up marketing of their cards directly or through area institutions. Dominion Federal Savings and Loan, for example, is an agent for Marine Midland Bank in New York. Dominion gets fee income on the Visa and MasterCards it issues for the New York bank, without taking on any liability.

Citicorp markets its Choice card directly. Among the privileges extended to cardholders are a rebate of 1/2 of 1 percent on all purchases over a total of $600 each year, and credit life insurance. Citicorp has applied to the Federal Reserve to allow its customers once again the opportunity of making deposits to interest-bearing accounts called Choice Purchase Plus. Before the option was disallowed, the account paid 8 percent.

American Express markets its Gold Card through local banks. The Gold Card is a hybrid: payment for goods and services is due in full each month, but cash advances are treated like loans, subject to finance charges in monthly installments. While American Express issues the card, the credit limit must be approved by a local bank. Seven D.C. banks, 15 Maryland banks, and 11 Virginia banks now offer the Gold Card.

The interest rate on cash advances is determined by the laws of each state. American Express encourages individual banks to offer the Gold Card as a part of a package of services, so privileges accorded with the card vary. Moreover, additional privileges are available at extra charge. Some of the basic ones mentioned by American Express are no pre-set spending limit, a $1,000 weekly cash advance at U.S. banks, personal checks cashed at hotels, $1,000 in travelers checks disbursed at airport terminals and charged to the card, card replacement in 24 hours, $75,000 in travel insurance, and guaranteed hotel reservations. And for $85 a year extra you can use selected health clubs around the world.