There is a good reason why Elvin Hayes' 33-year-old Bionic Body hasn't begun to show its age. It may be only 31.

"I began school when I was 4, not 6 like the school officials thought," said Hayes. "In my town (Rayville, La), you got your kids in school as soon as you could. They never asked for birth certificates. You said you were a certain age and that was good enough."

Hayes agrees he born on Nov. 17, but not in 1945, as everyone else believes. "Make it 1947 if you want," he said with a sly smile. "It's been 1945 so long it's hard to change it now. But you would'nt be wrong if you say I'm 31."

Whatever its age, that body remains a remarkable work of ahletic art. At 6-foot-91/2 and 235 pounds, it would be absurd to call the Bullet forward "Little E." But saying Haves is big just because he is so tall is like saying Burt Reynolds is handsome just because he has twinkle in his eye.

Hayes has molded the gifts of that body-quickness, speed, endurance, one of the consummate physical specimens ever to play in the NBA.

And tonight his durability and skill finally may receive a suitable reward. Sometime late in the game against San Diego, Hayes could delight the Capital Centre crowd by scoring his 34th point of the contest, which would give him 20,000 for his 10-year-plus career.

Only none other players in NBA history have reached that plateau: Wilt Chamberlain, Oscar Robertson, John Havlicek, Jerry West, Elgin Baylor, Hal Greer, Walt Bellamy, Bob Pettit and Kareem Abdul-Jabbar. Only Chamberlain, Robertson, Baylor and Abdul-Fabbar did it faster.

At the same time, he will become only the sixth player to have scored 20,000 points while also pulling down 10,000 rebounds (he has 12,1275 for his career), joining Chamerblain, Baylor the gifted magician, achieved these notable records in quite the same manner as Hayes. He has missed only five games in his career (including one because of a death in the family) and has averaged 43 minutes in 843 contests during that span. And he has done it by running the floor like a guard, blocking shots like a center and shooting unlike any other forwar.

"What makes Elvin so remarkable," said Bullet Coach Dick Motta, "is the speed at which he plays games. You don't see him loafing out there very much. No big man has ever got up and down like he does every night. At the pace he keeps, it's surprising he didn't burn himself out after five years in the league.

"He's just a marvelous athlete. The things he can do, noght in and night out. I didn't really appreciate it until I came here and watched him for a seson. He's pure basketball skill."

All this by a player who once wished he would stay short and skinny. When he started to sprout near the end of high school (he was 5-10 before his senior season), he began having trouble finding clothes to fit and shoes that felt comfortable, and it was embarrassing.

"I remember going to a football game and not having any shoes big enough," he said. "So I wound up wearing my cousin's shoes and putting my toes in them and walking on the heels.

"Now they make clothes that fit big people, but when I first got big, noting looked good. You were stuck wearing Army-Navy type shoes and coats that rode up on your back.

"It wasn't any fun being tall."

But now living inside the Bionic Body is scarely a hardship. He is wealthy (he just signed a $450,000, three-year contract extension), famous and, since the Bullets won the NBA title last season, content with his career.

"I remember how I dreamed about just playing in the pros," he said. "Now, to have played this long and to be this close to something so significant, it's very rewarding. Look at how many players there are who have never done it."

From a distance, the body that has helped Hayes achieve all this glory appears taut and on the thin side. But up close, Hayes is a mass of upperbody muscle and strength that tapers to a slim waist and long, springy legs.

It is a form meant to play basketball: not too heavy, yet physical requirements of the sport; agile enough to overwhelm most forwards and compete with most centers.

It gives him the coordination to master one of the game's most difficult shots, the turnaround jumper, which requires precise timing. It gives him the ability to withstand injuries that many players would need a week to overcome.

Hayes has a high pain threshold coupled with a will that refuses to allow him to be sidelined. Only a broken nose, a badly sprained wrist and a heavy dose of the flu have kept him out of uniform in the NBA, and that was after never having missed a game in either high school or college.

"I don't want to rest in games," he said, "Lots of times when they take me out, I say, "Why rest me? I haven't even worked up a sweat."

"When I first started playing basketball, I sat on the bench. Never again, I told myself. Besides, in high school, we played 50 or 60 games a season and all we did is run, run, run. I never came out and I built up stamina. I play better when I play a lot."

Motta tries to rest Hayes more than See HAYES, B3, COL.1 HAYES, FROM B1 HIS PREVIOUS COACHES DID, BUT HAVING HIM AS A BENCH COMPANION IS SOMETIME WORSE THAN HAVING HIM FATIGUED ON THE COURT.

"ELVIN," SAID MOTTA, "NEVER STOPS TALKING ONCE HE COMES OUT OF A GAME. 'WHEN CAN I GO BACK IN? WHY AREN'T WE DOING THIS?' IT'S EASIER SOMETIMES TO LET HIM PLAY.

"BUT WHEN YOU PLAY AS WELL AS HE DOES, I GUESS YOU HAVE A DESIRE TO STAY IN GAMES. 'E' LIVES AND EATS BASKETBALL. IT CONSUMES HIM. HERE'S A CASE OF SOMEONE WITH ABILITY THAT DONE HIS UTMOST TO PERFECT HIMSELF."

ONCE HAYES DISCOVERED BASKETBALL, THE DEVELOPMENT OF HIS GIFTS CAME NATURALLY. HE HAS NEVER LIFTED A WEIGHT. HE DID SPECIAL EXERCISES, MAINLY PUSHUPS, ONLU FOR ONE PROLONGED PERIOD-AFTER HIS ROOKIE PRO YEAR-WHEN HE FOUND A 6-91/2, 215-POUND CENTER COULD BE PUSHED AROUND EASILY BY CHAMBERLAIN, BELLAMY, UNSELD, WAYNE EMBRY AND OTHER NBA titans.

Nor is he particularly protective of his body. He doesn't smoke or drink, but he also eats only one or two meals a day, gets by frequently with three or four hours of sleep and rarely exercises in the offseason.

Is that any way to trat a body?

"Hey, it's just habit," said Haynes, laughing. "I'm always up by 7 a.m., even if I get to bed just a few hours before. I got into that habit when I was a kid and we had chores to de before school. But I've got to have an afternoon nap. I need those two hours everyday.

"I don't need much food to keep me going.On game days, I'll eat two meals but on off days only one.I like lots of rice and beans and good old Louisiana food.I don't eat fish on game days because it doesn't give me strength. And I never try to get too stuffed.

"I think one reason I've stayed so healthy is because I don't do much during the summer. Why wear yourself out unnecessarily? That's how people get hurt. You start taking shortcuts, don't play all out and something happens. By laying off, I always feel rested during the summer.

"When I do get hurt, the first thing I ask is: 'Can I get hurt if I play on it?" Then it becomes a state of mine. When the doctor says go, I play and forget the pain. Even now after 10 years, I still think positively. I don't feel there is a player who can run me or outjump me."

But occasionally even the best-conditioned athlete can have problems. During a physical exam prior to this year's training camp, doctors didn't like how Hayes' heart was functioning. They sent him to Georgetown Universtiy to undergo a stress test on a treadmill.

"They got the test going," Hayes remembered, "and pretty soon the guy in charge calls in a couple of students. Then a few more. Finally there is a whole group in there.

"Hey, I'm getting worried. I want to know what is going on. But they start talking out loud. "Look at how this heart is functioning. This is how a well-developed heart is supposed to operate. Wow.'"

"That's why when I stopped worrying."

But what else do you expected from a Bionic Heart, whether it's 33 or 31?