The old credit unions are adding new twists to handle your money

Looking at all the ads, one could get the idea that banks and money market funds are the only ones that know what to do with your savings. With claims and counterclaims of high interest rates, safety, and ''check writing privileges,'' the advertisements would like you to think that, when it comes to managing your money, you have a choice between banks and savings-and-loans on one side and money funds on the other.

There is another place for your money, however, that is getting more sophisticated and competitive. The only question is: Are you eligible?

This seemingly exclusive financial club is the credit union, that collector of small deposits and purveyor of low-interest consumer loans. While credit unions do not have the glamorous image of the money center banks or the high-flying money funds, they do have more than 46 million members and over $78 billion in savings.

That may seem small in comparison with more than $200 billion in the money market funds, but almost all credit union deposits are from individuals, while half or more of the assets in money funds come from institutions and corporations.

Despite their 46 million members, the credit unions think there is still plenty of room for growth. A survey last year by the Credit Union National Association (CUNA), the credit union trade association, found that while 20 percent of all adult Americans were credit union members, 24 percent said they were eligible but had not yet joined a credit union. These are the ones the credit unions are after.

There are also many people who are eligible to join a credit union but don't know it. There may be a credit union in their hometown for residents of that town, or a credit union in one company may have expanded to take in the workers at another factory nearby or one producing similar products.

A key to attracting some of these people is the US Central Credit Union, an organization CUNA calls the only private, nationwide banking system in the country. US Central acts like a national bank for the credit unions, giving them liquidity, professional guidance, and correspondent services.

US Central began in 1970, and stayed fairly small for a decade. But since September 1980, CUNA spokesman Howard Cosgrove says, its assets have ballooned from $2 billion to nearly $8 billion, bolstered by higher savings, fewer loans at local credit unions, and the attraction of several new services offered by US Central.

US Central is made up of 42 ''corporate'' (state or regional) credit union organizations, which provide financial services, like local check clearing and professional advice, for some 20,000 individual credit unions throughout the US.

To compete with money market funds paying 81/2 percent interest on a $1,000 deposit and offering check writing, many credit unions are offering rates that are close or equal to these returns. They also have competitive rates on their ''share draft'' accounts, the credit unions' equivalent of a checking account. At some credit unions, interest on deposits is also close to the banks' new money market and Super NOW accounts recently approved by federal regulators. And because credit unions' expenses and their account fees are often lower, the real rate of return is even closer.

Backed by US Central, many credit unions are also either moving into or exploring such high-finance operations as money market funds invested in US government-backed securities, discount brokerage accounts, and individual retirement accounts.

Mr. Cosgrove acknowledges that many credit unions, however, have decided not to take in all these fancy new services and keep expenses as low as possible. Here, he said, members are happy with just a deposit account and low-interest, easy-term loans.

''But the majority of the members do belong to credit unions with other services,'' he said. For these people, US Central and the expanded services it provides make a good excuse to join the once-stodgy credit union. 'Stanger Trust' for investments

My neighbor sold some investment property and said the proceeds were placed in a ''Stanger Trust'' where the capital gain is tax-deferred and the money can be reinvested in investment property at a later date and the capital gains remain tax deferred. The Internal Revenue Service in Portland, Ore., says it knows nothing of such a trust and has no publications covering it.

What is a Stanger Trust? Is it legal? Does one have to consult a tax lawyer or certified public accountant (CPA) to get information on how to make use of it? - C. H. To start with your last question: Yes, you should consult with a tax lawyer or CPA. The name ''Stanger Trust'' comes from a tax case heard in the US Court of Appeals for the Ninth Circuit, which covers the Northwest. The court ruled in favor of an arrangement similar to the one you describe set up by someone named Stanger.

While you may be able to set up such a trust in your part of the country, remember that its legality has not been upheld nationally. This is an example of a case where a tax-saving idea may be legal in one part of the US but not in another, because of differing court rulings. So anytime you hear of a new tax idea, whether it is being used in your part of the country or some other area, check it out with some tax attorneys or CPAs. It is possible that one of these professionals has heard of it while another has not. If you would like a question considered for publication in this column, please send it to Moneywise, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115. No personal replies can be given by mail or phone. References to investments are not an endorsement or recommendation by this newspaper.