Cancel the call to Perry Mason. Tell Sherlock Holmes to go smoke his pipe. We don't need Mickey Spillane, either. The mystery of how the San Antonio Spurs thumped the Bullets by 21 points has been explained by Doug Moe, the Spurs' coach. Defense did it.

This qualifies as news. Most witnesses believe San Antonio last played defense against Mexicans at the Alamo. Numbers tell us the Spurs led the NBA in scoring and also gave up more points than anyone else. Defense, for the Spurs, was thought to be those three or four seconds between George Gervin thrill shows.

Not so, Moe insists. He insists with passion. He read the local newspapers yesterday and said he cracked up. He couldn't believe how the Bullets had been portrayed as semicompetent bumblers who couldn't hit Bella Abzug's hat from three feet.

"What are we then-garbage?" Moe said. "We're a pretty good basketball team. Unless you're blind, you can see that. The key to that game was that our defense completely shut off what they wanted to do. But I read the papers and all I see is how they made a lot of turnovers and didn't shoot well."

Moe is an open and friendly man who, in his days as a pro player, worked on defense. To say his Spurs don't play defense-the conventional image of the team is that it runs and shoots more than the James gang ever did-is to insult his hoop heritage.

"It just cracks me up," he said, slapping a palm against his temple. "We laugh about it. No one here even mentioned our defense. Why? They're afraid to. We have a reputation. Nobody believes we play defense. Like, if we made a lot of turnovers, everyone would talk about how great the Bullets' defense is. But if the Bullets make the turnovers, we don't cause them, they're the Bullets' fault.

"Because we give the image of carefree run and gun, anthing we do defensively nobody can see. They have no idea we play defense. But, Hey, do you know why Elvin Hayes only got two shots the first 18 minutes of the second half?"

At midnight after the game, Perry Mason was called in on the case with Holmes and Spillane in the bullpen. No one had come up with a clue when Moe, at a lunch table yesterday, confessed that the Spurs had kidnaped Hayes and taken him out of the Bullets' offense.

"We had heard the Bullets' guards were in a slump, but we didn't care," Moe said. "We're more concerned with Bobby Dandridge and Hayes. Hayes and Dandridge, Dandridge and Hayes. They've beaten us time and time again.

"Wo we would double up on them sometimes."

By doubling up, Moe means a San Antonio guard would leave his assigned man and help play defense against Dandridge and Hayes. That leaves a Bullet guard open for an instant, but San Antonio, unlike some teams who have tried this strategem, does not double the big boys every time they get the ball. The Spurs want some unpredicatability about the double coverage so the Bullets cannot adjust to it easily.

"If anyone would wake up, they'd see our defense was good," Moe said. "Like, how did we play against Hayes?"

Some eyes, perhaps dozing, saw the Spurs' Mike Green going against Hayes, occasionally playing alongside him to discourage passes in to him.

"Not at all," Moe said. "Green was dead behind Elvin all the time. And then we'd drop a guard back to help out."

One need not be Albert Einstein, or even Charo, to decide it is smart to play two men against Hayes and Dandridge, especially when the Bullet guards are shooting so terribly it makes little difference if anyone guards them. And Moe knows just as well that the maneuver is not guaranteed to work again. Hayes and Dandridge can score from 17 feet in the dark.

But as long as someone was asking, Moe campaigned for his defense. As beautiful women want to be loved for their minds, three-points-a-minute basketball teams want to be loved for their defense. And when someone asked if a guard-oriented offense could win a seven-game series - the Spurs' offense revolves around Gervin and James Silas, who are averaging about 50 points a game - Moe turned evangelist again.

"What's the longest shot Silas took?" Moe said.

Maybe 15 feet.

"What's the longest shot Gervin took?"

Ten feet.

"So what the hell is 'guard play'? Our guards might be doing the scoring, but look where they are scoring from. They're scoring from forward territory. They're scoring from the same places Hayes and Dandridge do. Our guys don't take 'guard' shots."

It should be noted that Moe's small lectures yesterday were designed as educational and not meant to insult the Bullets. Fact is, Moe forever disqualified himself from admittance to the Terry Furlow School of Verbal Aggression by delivering a monologue in praise of the Bullets. Moe said:

"The Bullets are so tough, both physically and mentally, that they'll come back Sunday. They come back probably better than any team in the league. That's how they were able to win two games at Atlanta. Do you know how hard that is to do? Atlanta can run you out of town but the Bullets went down there and won twice. That takes guts.

"The guards aren't shooting well right now, but they could bust out of it Sunday. They're good shooters. Don't forget, the Bullets' guards won the series against us last year.

"I'm looking for a tough game, and that's what the Bullets are good at. We had everything going our way down the stretch in the first game. The Bullets couldn't get the ball in the hole, they made bad passes, everything went wrong for them.

"Well, the same thing could happen the other way. If we aren't ready, the Bullets can blow us right off the court. There's a real possibility the Bullets can blow out early." CAPTION: Picture, no caption, By James M. Thresher-The Washington Post