The Washington Bullets are not the only team that has trouble drawing spectators at home for the National Basketball Association playoffs. CBS, which televises NBA games with an impressive array of talent, isn't attracting as many viewers as it had expected.

After the first two weekends of playoff coverage, the network's ratings were down 34 percent from last year for Sunday afternoon games and 13 percent for late Friday night games. This follows a 5 percent decline in viewership for the seemingly endless regular season.

CBS is completing the second season of a four-year contract, the terms of which call for it to pay the NBA $47 million in rights fees. "If the situation doesn't improve over the next two years," says one concerned network executive, "pro basketball key League - right off national TV."

Why the slump?

CBS suspects that last year's ratings got a healthy boost from curious viewers getting their first look at David Thompson, Julius Erving and the other jewels of the defunct American Basketball Association who were playing in the NBS for the first time. This year the novelty, if not the enduring enchantment for the true fan, has worn off.

Moreover there is speculation that most people, especially in the Midwest and Northeast, do not want to stay indoors and watch basketball on Sunday afternoons now that spring has sprung after a miserable winter.

Basketball is a winter game. But the NBA's elongated schedule gives us the day days of the regular season during the sport's logical time period and the surging excitement of the playoffs when the weather has turned nice and few people really care about hoops any more.

Dr. J may be fascinating, but he can't compete with the Sunday sun when flowers are in bloom.

CBS has a geat deal of influence on playoff scheduling, but thas little alternative but to make them stretch from now to eternity.

The network knows that interest will dwindle the longer the playoffs go into the warm weather months. But it has no other time but Sunday afternoons to schedule the games.

"Sunday night? If you pre-empt Archie Bunker, your switchboard lights up," says the CBS man."Monday night? Pre-empt "M*A*S*H" and your switchboard explodes. The basketball people who tell you it will go in prime time are crazy. The only sports that go in prime time are heavyweight championship flights, pro football, the World Series or some super event like the Olympics."

Evidence to support this conclusion has recently come from ABC's Monday Night Baseball. Last week it was clobbered in the ratings by CBS's "National Collegiate Cheerleading Championships," which drew almost twice as many viewers in New York as the Yankees-Orioles game and one-third more in Chicago than the Cubs-Phillies game.

CBS is committed to televising some of the best-of-seven NBA championship series games in prime time, but the prospects for a big audience are bleak.

Ratings figures are little more than numerical gibberish to the average man in the street, but a comprehensible gauge is "audience share" - the percentage of sets in use at a given time that are turned to a particular show.

Last Sunday, the first game of CBS's regional doubleheader (Bullets-San Antonio or Philadelphia-New York) drew a 24 share. The second game (Seattle-Portland or Denver-Milwaukee) got a 19 share.

In the same time period, ABC got an 18 share for auto racing, 19 when it switched to boxing, and 21 for "Wide World of Sports" (George Willig climbing a rock, lives). NBC got 17 percent of the nation's turned-on sets with the Houston Open golf tournament and 19 percent for its anthology show, "Sports World."

The previous Sunday CBS got a 22 share for NBA's Game 1 and an 18 share for Game 2. ABC captured 21 percent with boxing and 26 percent for "Wide World" while NBC trailed with only an 11 share for women's tennis and 16 for "Sports World."

Adding up the shares for both weekends, it is obvious that the largest bloc was tuned to stations showing syndicated shows, old movies or other local programming.

A week ago the late Friday night game on CBS (Seattle-Portland or Denver-Milwaukee), starting at 11:30 p.m. in the East, got a 23 share, compared to 25 for a "Baretta" rerun on ABC and 34 for "The Tonight Show" on NBC. The previous Friday, the Seattle-Los Angeles game got a 24 share, the same as "Baretta," while Johnny Carson again prevailed with 32.