The quartet has no name, no recording contract and no hope of reaching an audience larger than its own members. But the group has been playing together almost every Sunday night for 20 years.

Last Sunday was no different. Violinists Fred Carlson of McLean and Marilyn Schwaner of Alexandria arrived at the Georgetown home of cellist Richard Osius for an evening of chamber music. Violist Monroe (Monty) Vincent, an original member of the quartet, was recovering from surgery and unable to attend. It was agreed that no lesser excuse would have kept him away.

He was replaced that night by violist Debby Baker of Silver Spring, one of about a dozen people outside the group who can be counted on to fill a vacancy on short notice.

If theirs is a remarkably stable group, many amateur players prefer to lead a more unstructured musical life. Most rely on word of mouth to find other interested players, but more than 200 musicians from the Washington area are listed in the Amateur Chamber Players Directory for North and Central America. The directory lists musicians by address, instrument and level of proficiency.

Among more than 50 Northern Virginians listed in the directory is Lee Fairley, a member of the association since its founding in 1947. Fairley, a retired foreign service officer, has been playing chamber music since he arrived in the area in 1941 as a reference librarian for the Library of Congress.

The directory lists 3,000 musicians in the American edition and nearly 1,000 people in the overseas edition. In fact, the founder of Amateur Chamber Music Players Inc., Leonard A. Strauss, devised the idea of a chamber musicians network in despair of having to play his violin alone in hotel rooms on his frequent business travels.

Dr. Albert Casabona, an orthopedic surgeon from Oakton, recalls a recent trip to Honolulu, where he called people on the list who took him to their home for an enjoyable afternoon of quartets. Chamber playing visitors to this area might find Casabona equally willing to extend the invitation for an evening of string quartets at his home. He joked that it's sometimes difficult to reach him at work, but that his secretary knows that she can always put a chamber music call through.

Casabona, like many devoted amateurs, studied his instrument seriously as a child, but turned to another career. That decision was due in part to the influence of his parents, both members of the prestigious Cleveland Symphony Orchestra under the baton of George Szell. "This is why I'm a physician," he said, "because my parents were both violinists and they didn't want me anywhere near the business."

Now he is content to play with friends, while introducing other amateurs to one another. It was his introduction that brought Osius into the Sunday evening gatherings five years ago when there was an opening.

The group tackles even the Beethoven quartets, among the more complex works in chamber music. Under the watchful gaze of an oil painting of Osius' great-great-great-grandfather, he plays music held by a freshly polished wooden music stand that belonged to his father, a cellist in string quartets for more than 40 years.

Nearby his 3-year-old daughter Lizzie, who had just begun violin lessons, traded glances with her father, perhaps thinking of the day when she would be doing the same thing.