Basketball is an expensive hobby for John Harris. Although some are content to buy a ball and a pair of sneakers and head out to the playground, Harris, a 43-year-old carpet salesman, springs for the round-ball needs of about a dozen players who serve as both a basketball team and circle of friends to him.

Expenses for Harris' team now called the Maryland All-Stars, were approximately $7,900 during the 1976-77 season - $3,300 of it out of his own pocket, he said. The team that year compiled a 56-6 record and finished as runnerup in the National Amateur Basketball Association tournament.This past season, Harris was forced to keep the expenses down to less than $5,000 by playing fewer games (26-3); $2,600 of that outlay was spent on a recent trip to Chicago where the All-Stars, representing metropolitan Washington, defeated the local team, 105-97, to take home the national title.

As a reward, the team expects to represent the United States on a European tour, although the trip has not yet been arranged.

When Harris, a resident of Indian-head, Md., formed the team 14 years ago, it was called Ely's All-Stars and was sponsored by a Charles County furniture store, which Harris managed. Seven years ago, the store was sold and although Harris still works there, it no longer covers the expenses of the team's games outside the county. The team was too good for local competition and Harris was forced to foot the bill himself to go elsewhere to play.

Harris shrugs off the cost of the operation as "an expensive hobby," which provides a good excuse not to "work 90 hours week . . . when there's not basketball.

"Many people like to boat. Maintenance on a yacht costs more than this a year. Some people spend more than I do on cars. This is my hobby-type thing and it helps me sell carpets, too. When I'm at a tournament, I'm passing out cards."

The players appreciate his efforts. "I always ask him, 'John, Why?" said Ollie Johnson, 35, the team's 6-foot-7 center who has played for six years on the All-Stars. "I would say he's a very unique individual. "I always say I'm going to write a book about the sitution. To appreciate him, you have to know him. He's one in a million."

Harris' team is an interesting mix of youth and age, and a broad variety of occupations. On the team there are several teachers - one who coaches an area high school squad - a junior high school assistant principal, a government worker, a personnel officer, an insurance salesman and a graduate student. Johnson and player-coach Tony Upson are the elder statesmen of the club, while guard John Holloran, the first man off the bench, graduated from George Washinton University in 1977.

Joining Johnson, an Oxon Hill resident, in the starting lineup are Aubrey Curry, a 6-2 guard from Upper Marlboro; Lionel Harris, a 6-3 guard from Northwest Washington; Earl Hawkins, a 6-3 forward from Waldorf; and Bill O'Tey, a 6-6 forward from Northwest Washington. Every member has played college ball, several have had shots at making the pros. Johnson played briefly for the Boston Celtics of the National Basketball Association.

Upson said the blend of personalities has kept the All-Stars close and made them more comfortable with the squad's concept of team play, which was a main factor for the team's success at the national level.

"Basically, we've been together so long, we know each other well," he said. "Most of the teams that go (to the nationals) are like all-star teams. They just get together for a short while and they're running and gunning. We have a pattern offense.Each man has his role."

For Harris and members of the team, camaraderie extends off the court to the E.A.S. (Ely's All-Stars) Social Club, which meets often during the season and two or three times between campaigns.

Johnson says he still plays basketball because he likes "just being with people other than work who you can get along with and understand. We have a lot together as far as temperament . . . as far as getting together and working for a common goal.