Moses Malone believes that when he puts up a shot, only two things can happen: either he will score or get the rebound.

The Houston Rockets' 6-foot-10, 240-pound center has been doing both regularly. His average of 40 points and 19 rebounds during the last seven games represents the NBA's most impressive short-term individual statistics this season.

Thursday night Malone had 21 offensive rebounds--breaking his own NBA record--in a 117-100 victory over the Seattle SuperSonics. He also scored 38 points.

The 21 rebounds broke Malone's record of 19, and came in what was probably the most physically dominating one-man performance in the NBA this season. The SuperSonics, one of the NBA's biggest and most physical teams, had won seven straight games and 16 of their last 18. Malone outrebounded the SuperSonics by himself, 32-29.

"I was helpless against him," said Jack Sikma, Seattle's 6-11, 230-pound all-star center. "We were all helpless."

That has been a common feeling lately. Malone had 53 points in one game, 47 in another and has had 20 or more rebounds four times in the seven games.

Larry Bird and Magic Johnson may be more exciting, but when it comes to the most elementary skills of the game, scoring and rebounding, Malone has become the NBA's most dominating complete player.

He is leading the league in rebounding, averaging 14.1 a game, and is third in scoring, at 29.5. The last person to lead the NBA in both categories was Wilt Chamberlain in the 1965-66 season.

"The only other time I can remember playing this well was in high school," said Malone, who went directly from Petersburg (Va.) High School into professional basketball despite signing for a scholarship with the University of Maryland.

"There are a lot of reasons for it, but it's happening mainly because I work hard. I've lost some pounds, my body feels good, I'm getting my rest.

"I never thought about the game in terms of having fun, but this is fun. The difference is that we're winning (26-22). Big points and big rebounds aren't fun when you lose."

Malone doesn't go much for finesse, either. Once he gets the ball, he turns to the basket and immediately either puts up a shot or uses a power move to the hoop.

The SuperSonics tried to control Malone by alternating Sikma and 7-2, 270-pound James Donaldson as his defenders. They tried playing behind him, playing on the side, fronting him, hacking him, smacking him and whacking him. Nothing worked.

"Whatever you do, don't make Moses mad," said San Antonio Assistant Coach Morris McHone. "Just put somebody on him to bother him a little bit, but don't get physical with him because he'll eat you up. He loves that."

The Washington Bullets, who have been impressive on this current trip with victories over San Antonio and Dallas, play the Rockets Saturday night at the Summit (WDCA-TV-20 at 9). Bernie Bickerstaff, the Bullets' assistant coach, scouted the Houston-Seattle game and left shaking his head.

"The best way to defend against Moses might just be to let the ball go into him, because when you don't, they swing it to the other side and then he can get whatever position he wants inside," Bickerstaff said. "You know if the shot misses, he's going to get the rebound and then he's got a layup."

"The key to our winning is that Moses is getting the rest of us involved, too," said Rocket guard Calvin Murphy. "You have the confidence to take a shot because you know if it misses, he'll get it back for you. Everyone knows you can't guard him with one man, and that's what opens everything else up."

Malone's style is unique. He usually looks as if he's disinterestedly sauntering up the court. Then he suddenly moves into position.

Most opponents double-team him, with a guard dropping back to front him. Malone usually beats that by turning toward the basket as soon as he gets the pass. He usually has three players around him every time he shoots, but he is so strong, his shot seldom is blocked. When he shoots, he jumps at a backward angle, shaking defenders off him.

But it is his offensive rebounding that makes Malone such a threat.

Even when he can't control the ball outright, he has a knack for tapping it to himself. He doesn't always jump high, but he jumps quickly and snatches the rebounds instead of waiting for them to come to him. Malone also has a great instinct for getting into position for rebounds.

During Thursday's game, Bill Willoughby took a high, arching 15-footer from the left side. Sikma and Donaldson formed a shield under the basket in front of Malone, who was in the middle of the lane. Malone glanced at the ball, sensed it was going long and positioned himself to the right of the lane, away from both Sikma and Donaldson.

The ball bounced off the rim to him and he made a layup.

"Pound for pound, I don't think any player can match Wes (Unseld) when it comes to rebounding," said former Bullet Elvin Hayes, now a Rocket. "But I don't think any player is as devastating as Moses on the offensive board, because he is so active. The way to stop a good offensive rebounder is to screen him off the board, but you can't screen Moses away with even two men."

Malone does have a weakness--he tends to drift a little too far from the basket on occasion and take a no-arc 16-foot jumper, which is out of his range. But Coach Del Harris says he can live with that.

"Mo has earned the right to take that shot if he feels like it," Harris said.