Once, it was a model of cooperative enterprise, proof that a business, voluntarily organized and owned and controlled by members, could compete against traditionally for-profit-only firms. That was 40 years ago.

In recent times, the Silver Spring-based Greenbelt Consumer Services, Inc. - the second largest consumer cooperative in the country - lose its way.

Some say it grew too big for itself. Others, that the former Greenbelt management team lot sight of their commitment to consumer involvement and pursued dreams of empire instead.

At one time, the Greenbelt cooperative was an impressively large business: 22 supermarkets, 5 pharmacies, 10 gas stations. Today, it is down to 12 supermarkets and 7 gas stations. It had been trying to erase at $1.5 million deficit left over from the 1970-72 period, but last year suffered a loss of $462,-00. The book value of its stock has fallen from $10 per share to $5.58 as of January, 1977.

Most serious of all, Greenbelt as not refunded any profits to its membership since 1959. Called "patronage refunds," these returns are a unique feature of cooperatives and distinguish them from other forms of private enterprises. They are generally awarded in proportion to the amount each member spends at the co-op.

Despite its troublesome past, Greenbelt is not about to abandon its 38,500 members. Its chain of Scan furniture stores have been operating profitably throughout the dark years and are continuing to expand. Last year, a tenth Scan store opened for business.

More significantly, the cooperative has filed with the Securities and Exchange Commission for permission to seek new members.

Much of the guarded optimism among the co-op's staff centers around their new chief executive, Roy Bryant. He was hired at the end of last year from the large and successful Berkeley Co-op, bringing with him 30 years of food industry experience.

Why leave a sunny and profitable operation on the West Coast for something uncertain and less appreciated in the East? Because, say those who know Bryant's mind, co-ops have become a way of life for him and for many in the West, as he thinks they can become for many in the Washington area.