WATCHING summer basketball league games in Washington requires a little fortitude. It may mean sitting scrunched elbow-to-elbow in one gymnasium, battling sauna-like heat in another or constantly looking toward the sky hoping the thunder clouds will hold off.

Those inconveniences are minor, however, for basketball lovers and self-proclaimed gym rats eager to fill their evenings with free, up-close looks at professional and college stars such as Frank Johnson of the Washington Bullets, John Battle of the Atlanta Hawks, Ed Spriggs of Howard University and the Los Angeles Lakers, Danny Ferry of Duke, Keith Gatlin of Maryland, or former University of the District of Columbia all-America Earl Jones. And that's just in the Urban Coalition League games in the Dunbar High School gym.

There are three other leagues with top talent free for the viewing:

The King Cobra League in Prince George's County is stacked with such players as Billy Martin, the former Georgetown star and current Indiana Pacer; ex-UDC star Michael Britt; and Michael Graham, who as a freshman helped lead the Hoyas to the NCAA title.

The Kenner League at Georgetown's McDonough Gymnasium offers players like the Hoyas' Reggie Williams, Duke's Billy King, American University's Frank Ross, and Mark Tillmon, last year's Washington-area boys player of the year. And the Hobson League in Montgomery County showcases such athletes as former Holy Cross star Dave Mulquin and former George Mason University player Terry Henderson.

"There is no better summer basketball than right here," says Urban Coalition League commissioner Jim Wiggins. "We take pride in saying, 'You can imitate the Urban Coalition League, but you can't duplicate it.' " The other local leagues speak with a similar pride.

The defense may be a wave and a wish, and the shooting touches can be slightly off from inactivity, but fans are treated to a show at every game: 6-foot-10 centers trying to prove they can score 20 feet from the basket; 5-foot-10 guards rarely passing up a chance to end a fast break with a breathtaking dunk.

And anyone questioning the competitiveness of summer ball will have his doubts dispelled, especially during league playoffs, which run from the final week of July through mid-August. These championship-level players are satisfied with nothing less than a title, even if it is simply for a small, token trophy.

"You could say every game is like an all-star game," says American University Coach Ed Tapscott, who, like many major college coaches, often drops by the summer league games.

The Urban Coalition League, which mixes professional and collegiate players, draws standing-room-only crowds of more than 2,700 every Friday, Saturday and Sunday. Part of the fan attraction, Wiggins says, is the element of surprise.

The weekend schedule for the 10 teams is established only one week in advance. Teams have rosters, but if a big-name player just happens to show up in the gymnasium, the league makes sure he has a team to play on.

"You have to be here almost every game or you might miss someone like Ralph Sampson just showing up and playing," adds Wiggins. And if general manager Bob Ferry of the Bullets calls up in the middle of the week and says he wants to send a team of Bullets players down one day, "well, we don't turn him down. We just change the schedule a little, and no one ever minds."

The surprises extend beyond who will show up. Take a recent game between P.J.'s Pub, a team made up of unnoteworthy current and former Loyola of Baltimore players, and Executive III, starring the Hawks' Battle, a 6-2 guard who has been averaging more than 50 points per game. With two seconds remaining in the game, Battle was isolated on the left side to try a tying shot. But the crowd favorite, 5-8 Mo (Go Go) Hicks, stripped him of the ball, and P.J.'s won 137-135.

Those kinds of defensive heroics are a rarity, of course: Pouring the ball through the hoop is Job 1. But "the players try as hard at these games as they do when it counts during the season," says fan Wilson Richardson of Northeast D.C., his eyes glued to the action at a recent Kenner League game. "They are playing to stay in shape, but they know anyone who comes out here would be disappointed if they did not give their best."

Kenner games, which do not allow professional players, draw several hundred spectators, but the most important fans are the four oscillating ones in each corner of the steamy, unairconditioned McDonough Gymnasium.

The King Cobra League, the newest area summer league for both professional and collegiate players, plays its regular season games inside at Forestville High School. Despite its recent formation, it's grown fast because it offers a chance to work in extra playing time with mid-week action against topflight competition.

The Hobson League, known as the Maplewood League until this summer when it was renamed after its founder, Howard Hobson, occasionally flirts with the big time, but it has remained a place where a group of neighborhood players can still enter a team that will play against current and former college stars.

Two of the three nightly games at Fleming Park or Hoover Junior High are played outdoors where fans sit on grass-covered inclines several feet from the out-of-bounds lines. The scoreboard is not fancy -- just someone displaying red and green cardboard numbers after each score.

For spectators, the compactness of each summer league home offers a different perspective on the stars.

"People get into the game more; they have that 'little thing' with the players because they are right next to them," says Wiggins. "Players don't just leave the court here like they do in big arenas. They get mobbed by the fans, and they still might get dressed and just go sit in the bleachers. They will sign autographs for hours. You just don't find that at the Capital Centre." DRIVING TO THE HOOPS

Here's where you can find the area's top summer basketball: URBAN COALITION LEAGUE -- Games every weekend through August 17 at Dunbar High School (First and N Streets NW). Friday at 6 and 8 p.m.; Saturday and Sunday at 2 and 4. Championship game Sunday, August 17, 4 p.m. Call 399-9788 for more information. KENNER LEAGUE -- Games every weekend through August 10 at McDonough Gymnasium (on the campus of Georgetown University). Friday at 6:30 and 8:15 p.m.; Saturday and Sunday at noon, 2 and 4 p.m. Championship game Sunday, August 10, 4 p.m. Call 583-2717 for more information. KING COBRA LEAGUE -- Games at 7 and 8 p.m. every Tuesday, Wednesday and Thursday through August 5. Regular season games through July 24 at Forestville High School, 7001 Betz Drive, Forestville. Playoff games starting July 29 at William Beanes Community Center, 5108 Diana Drive, Suitland. Championship game Tuesday, August 5, at 7:30 p.m. at Beanes Center. Call 699-2401 for more information. HOBSON LEAGUE -- Games Monday and Wednesday through August 6 at Fleming Park (end of Fleming Avenue off Grosvenor Lane in Bethesda); Tuesday and Thursday through August 7 at Hoover Junior High School (8810 Postoak Road, Potomac). Games nightly 6:30, 7:30 and 8:30 p.m. Championship game either Wednesday, August 13, or Thursday, August 14, at site to be determined. Call 468-4210 for more information.