A credit union can be a candy store of personal finance goodies: * Free checking with no minimum balance. * Free credit cards with as little as 13 percent interest.
* Car loans at cut-rates.
Unfortunately for most Americans, a ''Members Only'' sign hangs in the nearly 20,000 US credit unions that cater to employees of a particular company or group. But recently, many of these tax-free, cooperative ''banks'' have extended their welcome mat to others.
Credit unions tied to the sagging fortunes of smokestack industries are on a membership drive. ''It's a thrust for diversification and ultimately, for survival,'' says Robert Kratt, at the International Harvester-Farmall Credit Union, in Rock Island, Ill.
Two years ago, the future for this major tractor manufacturer - and its credit union - was ''tenuous, at best,'' Kratt says. Since then, 160 different companies have eagerly joined to share in the benefits once enjoyed only by International Harvester employees.
The nonprofit status of credit unions, which provide their 47 million members with an alternative to the local bank, usually makes for better rates on loans and savings deposits. Some 85 percent of all credit unions are tied to smokestack industries. But despite initial setbacks caused by recession, many are prospering.
Since deregulation of the industry in 1982, some of the larger credit unions have broadened not only their customer base but their services. Some organizations now offer 24-hour automatic tellers, money market funds, credit cards, and home loans.
''In 1983, we grew by 20 percent. Compare that to the 11 percent growth of savings and loans and 6 percent for banks,'' boasts Edgar F. Callahan, board chairman of the National Credit Union Administration.
Mr. Callahan is in Massachusetts today to receive a commemorative stamp issued in honor of the 50th anniversary of the Federal Credit Union Act. The dedication ceremony is to be held in Salem, Mass., the birthplace of Edward A. Filene, who is considered father of the credit union movement. His Boston-based store, Filene's (a Federated Department Stores outlet), is home to the oldest retail credit union in the country.
A year after passage of the Credit Union Act, which was a necessity for many workers because of the numerous bank closings during the depression, Mr. Filene said that the economic picture would improve when businessmen get over their ''age of scarcity thinking and adapt themselves to the age of plenty.''
Mr. Filene would probably approve of current efforts by industrial-based credit unions to ''adapt themselves.''
''Almost every steel mill in this country has a credit union that's trying to diversify,'' Callahan says.
The Tech Federal Credit Union in Crown Point, Ind., for example, served 10 companies a year ago. Nine were steel mills. Now, 21 organizations contribute to and share the credit union's $57 million wealth.
''We were pushed by layoffs,'' says Michael Hussey, general manager of the credit union. Almost 4,000 members had dropped out in one year. Today, they're recruiting at a rate of about 200 a month, says Mr. Hussey.
Bankers have not been as enthusiastic about credit union growth. ''The original purpose of the credit union was for people with a common bond to pool their savings,'' says Fritz Elmendorf, a spokesman for the American Bankers Association. But rather than legislate restrictions on credit unions, Mr. Elmendorf says the ABA seeks to free banks to compete more effectively.