Most persons assume a Visa card is a Visa card is a Visa Card, and that all Master Charge cards are alike. In fact, there are big differences. Suppose you and your friend have Visa cards and you go to the same bank to take out $2,000 cash advance loans with your cards. Suppose, too, that you both pay off your loans after exactly a month. The finance charge for you might be $60 while your friend's finance charge might be $20. Or take a similar, through less dramatic, situation - this time involving use of the Visa cards for retail purchases rather than cash advance loans. Suppose you and your friend have been carrying $1,000 card balances and each of you makes retail purchases totaling $500 on the 10th of the month. Your finance charges at the end of the month might be $10 higher than your friend's. Who pays more depend on which bank "issued" the card. There are about 20 Washington area banks issuing Visa cards, Master Charge cards or both. Each bank is free to set its own interest rates and other terms within certain limits set by law, and the bank you get your card through is the bank that takes the entire loss if you fail to pay off your balance. These banks simply affiliate with one or both of the national interchange systems - Visa (formerly Bank Americard) and Master Charge (the Interbank System) - for paper-handling convenience. In the past, many banks had their own cards with their own names. The Bank of Virginia Charge Plan is a surviving example. But customers who had these cards could not use them with merchants in other parts of the country. To solve this problem, since the mid-1960s most banks have affiliated with Visa or Master Charge. If you make a purchase in a distant city, the merchant can cash in your sales slip with an interchange-affiliated bank in the city, and that bank, in turn, can collect from your bank. In becoming a member of one of the interchange systems, a bank simply agrees to handle sales slips in this way and to follow a common card format. The major differences among cards affiliated with the same system have to do with: Interest rate. On balances resulting from cash advance loans, some banks charge 12 percent while others charge 18 percent. On balances resulting from retail purchases, Virginia banks charge 18 percent regardless of balance size, while Maryland banks are limited by law to 12 percent on the portion of a balance above $500. Because the District's legal interest rate ceiling is 11.5 percent, none of the District banks has considered it profitable to issue its own card. Method of computing interest. No bank charges interest on a balance resulting from retail purchases paid off in full within 25 days of the first billing. But if you carry a balance from month to month, some banks will start charging interest on each new purchase as soon as you make it, while others will give a free ride until you get your first bill reflecting the new purchase. Similar variations affect cash advance loans. Transaction charges. On a cash advance loan, some Virginia banks charge as much as 2 percent of the amount of the loan at the time of the loan on top of the interest charge. As a result, for the first month of such a loan, you pay the equivalent of a 35 percent annual interest rate. But none of the Maryland banks imposes these transaction charges, and not all of the Virginia banks have them either. To get the best of these various terms, you have to shop. Start by calling various banks and asking for truth-in-lending disclosure statements. These statements should enable you to make comparisons. Be warned that some are hopelessly obscure, but some are actually intelligible. If you cannot figure out what one says, you can check with bank personnel. But, again, don't count on a lucid explanation. You may get conflicting statements from different persons. Do not confine your shopping to the jurisdiction you live in. Some of the best terms for retail purchase credit are available on cards issued by Equitable Trust and Suburban Trust in Maryland. Anyone from the District or Virginia can apply. Also, consider getting different cards for different purposes.For large retail purchase balances, the terms of United Virginia's Visa card are not as favorable as those of a Visa card from Equitable Trust. But for a cash advance loan, the United Virginia card offers a 12 percent interest rate, compared to the 18 percent rate Equitable Trust charges most customers (except customers with credit limits exceeding $3,500). Before settling on one or more bank cards, you may want to consider two other alternatives: the independent cards and the "travel and entertainment card" cards. The terms of the independent cards, Central Charge and NAC, are roughly competitive with the terms of many of the bank cards, and some individuals whose credit histories do not qualify them for the bank cards find the independent cards easier to get. But these cards, which are not affiliated with banks or with national interchange systems, cannot be used to get cash advance loans and do not enjoy nation-wide acceptance for retail purchases. The "travel and entertainment" cards - American Express, Carte Blanche, and Diners Club - differ from the bank-issued cards in two important respects. They charge customers an annual fee - currently $20 to $30, depending on the card - and they expect you to pay off your balance from most types of purchases right away, preferably within 25 days of billing. In addition, the travel and entertainment cards have traditionally been limited in the types of purchases for which they are accepted. But they are now expanding into many new retail outlets, from auto repair shops to clothing stores. American Express has a special arrangement with some banks to market what it calls its "Gold Card," which is directly competitive with Visa and Master Charge cards. You can use the Gold Card to get cash advance loans, and you also can use it to extend the due date for payment of a retail purchase balance. If you do not wish to pay off a retail purchase balance within 25 days, you notify the American Express Company and it will tell the bank that arranged your Gold Card that it is to give you an automatic loan to pay off the American Express balance. From the point on, your obligation is to the bank, just as it would be with a Visa or Master Charge card. At several local banks, this Gold Card system is a particularly attractive arrangement. For instance, at Riggs Bank and Union First Bank in the District, you pay only 11.5 percent on balances that originate through use of a Gold Card. This compares very favorably to the 18 percent interest rate most common on Visa and Master Charge retail purchase balances.