FOR MORE than 2.3 million Washingtonians, a trip to the bank actually means going to a credit union. While even the largest credit unions in the state are still dwarfed by regional and nationwide financial institutions like Wells Fargo, Bank of America and the homegrown Washington Mutual, they have become a force to be reckoned with.

 In order to compete with banks for convenience and availability, credit unions have formed alliances to share resources such as ATMs, through the Co-op Network, now one of the largest ATM networks in the country. And more recently, they have adopted "shared branching," which gives members access to their accounts and services at any one of 1,600 credit union offices nationwide.

"The banks have had a many-years head start in putting branches out there," says Gary J. Oakland, CEO of Boeing Employees' Credit Union (BECU), the state's largest credit union. "And there's just no way with our size and nature that we're ever going to catch up from a branching standpoint, so let's share the branches that we have." Oakland says BECU has been opening a number of minibranches in area supermarkets, following a strategy that the major banks pioneered a few years ago. In fact, he says most of the transactions BECU processes arrive via ATMs, store-based mini-branches and banking over the Internet.

Although credit unions started out as savings institutions with tightly restricted membership rules and offering small loans, they have been morphing into something that looks very much like a bank, at least from the outside. And their expansion has hit a raw nerve among banks that find themselves increasingly in competition with them.

 BECU, for example, was formed in 1935 by 18 company workers. Today it is the fifth largest credit union in the country. Assets have gone from their initial $9 investment - 50 cents from each original investor - to more than $6.3 billion, and its loan portfolio is nearly $5.4 billion. BECU has also been expanding its reach, first by making family members eligible to join in 1973, then by adding a "once a member, always a member" rule four years later. By the mid-1980s, BECU had 96,000 members and $569 million in assets.

The credit union has also branched out in the services it can offer members, which now include checking (formally known as "share draft accounts"), ATM cards, CDs and IRAs, as well as Visa cards and home equity loans. In the early '90s, it spawned BECU Financial Service Organization to provide financial planning services and partnered with a mortgage company to begin offering mortgage loans.

Traditionally, credit unions were limited in the scope of services they could offer and, more significantly, in who could join. Members needed to have something in common, whether it was working for the same company or in the same profession (such as nurses and teachers), belonging to an organization or club, or living in a particular community.

In 2002, the Washington legislature loosened the rules. Since then, BECU has opened itself up to anyone who lives, works, goes to school or worships in the state. At last count, the organization had about 427,000 members, one among every 12 state residents. This year the credit union embarked on a major advertising campaign to recruit new members, helping it maintain an annual growth rate of better than 12 percent. Gary Oakland says it's essential for credit unions to attract new members, because that's their only means of raising capital.

Even relatively small credit unions, such as iQ in Vancouver, with 38,000 members and about $350 million in assets, have adopted the everyone-in-the-state formula for membership, although they have remained committed to their primary regions.