Not long ago things were simpler. There were three positions on a basketball team - guard, forward and center. Now, in the National Basketball Association, the game has evolved into one with five positions, each requiring its particular skills.

There is a point, ball-handling penetrating, small or No. 1 guard to set up and run the offense; a shooting, No. 2, big or off guard, to take the outside shot and provide movement without the ball; a small or quick forward to run and shoot and move the ball, and a power forward to rebound, set the picks inside and provide muscle. Then there is the center - still called the center - who brings it all together.

The top centers today are Bill Walton of Portland, Kareem Abdul-Jabbar of Los Angeles, Bob Lanier of Detroit, Bob McAdoo of New York, Dave Cowens of Boston, Dan Issel of Denver and Artis Gilmore of Chicago.

Walton is the best.

He isn't a top scorer, but he could be if the shot more. He is that rare athlete who makes all of his teammates better.

"Walton is the man right now," said George McGinnis of the 76ers. "You can surround him with average players and still win."

Walton has reasonable shooting range and can play with his back to the basket or facing it, opening the possibility for an inside pass or a drive to the basket. He is the consummate team player, the perfect person around whom to build a team. He blocks shots, rebounds and starts the fast breaks. Perhaps he also is the best passing center today. He is almost fundamentally perfect and has the right temperament. He loves to play and hates to lose.

All of the top centers have individual styles and strengths, but none can do all of the things Walton can do.

Abdul-Jabbar and Gilmore have fine inside games and their strong suit is putting the ball in the basket.

They want the ball low and, when they get it, they shoot rather than pass. Both are limited, though, and the farther they are from the basket, the less effective they are. Both seem to look only for what comes their way, saving most of them energy for offense.

Gilmore and Abdul-Jabbar get a lot of rebounds, but neither is a good rebounder. Neither is very aggressive and seems to come up only with the rebounds anyone 7 feet tall should get.

Abdul-Jabbar does have his sky hook, that he can shoot with either hand, and that makes him almost unstoppable down low.

Gilmore has an array of close-in shots, but none is unstoppable.

McAdoo is the best shooter among the top centers. He doesn't make many moves or drive much. He roams the floor until he gets the ball and fires it up. He plays more like a forward because he likes to face the basket as opposed to playing with his back to it.

Lanier, Cowens and Issel are perhaps the most versatile offensively because they can play with their backs to or away from the basket. All three also have great range on their outside shot, forcing the center outside with them. That, in turn, opens the middle.

Lanier and Cowens also are aggressive, tough rebounders, who also set screens.

Forward is perhaps the toughest position to play and the best athletes often end up there.

A forward has to be able to shoot, pass, rebound and set picks. A center doesn't always have to be a good passer and a guard doesn't have to be a good rebounder.

"Rick Barry is the ultimate forward," said Joe Roberts, the Warriors' assistant coach. "He can drive, shoot and pass. He is as well rounded as you can find. Most of that is training and early development. If you don't learn to dribble early, you never will.

"By the time you get to this league, there isn't that much changing of a player's game you can do."

Bullets' Coach Dick Motta is another who feels that Barry could be the best all-around forward in the league.

"He's the most clever assist man, he's the best clutch shooter and he's the man I would want to have the ball in the last minute of a tight game."

The votes Barry doesn't get as the best forward belong to Julius Erving of Philadelphia.

Barry and Erving are set apart from most of the others by their ability to do whatever situations demand - pass, drive or take a good shot from the outside.

Elvin Hayes of the Bullets has as much natural ability as Erving and Barry, but he isn't an innovator. He shoots a mechanical turnaround jump shot, sprints downcourt for dunks, shoots a straightaway jump shot and has an awkward drive to the middle. That is basically the extend of his offensive repertoire.

Hayes is considered a power forward. He is expected to rebound play defense and score. The other top power forwards are Maurice Lucas of Portland, George McGinnis of Philadelphia and Truck Robinson of New Orleans.

Barry and Erving are considered small forwards. The other top small forwards are Bob Gross of Portland, Bob Dandridge of Washington and Walter Davis of Phoenix, David Thompson of Denver.

Guard-oriented teams don't win championships often, but it is the guards who set the tempo.

Penetrators such as Kevin Porter of New Jersey, Norm Van Lier of Chicago, Tom Henderson of Washington and John Lucas of Houston make things happen.

As primarily ballhandling guards, they are quick, good dribblers and passers. They are not necessarily good outside shooters, but drive to the basket well.

Shooting guards such as Phil Chenier of Washington, Doug Collins of Philadelphia, Fred Brown of Seattle, Lionel Hollins of Portland, Calvin Murphy of Houston and Jo Jo White of Boston are bigger but not necessarily as good at handling the ball as the point guards. Their basic requirement is that they have to move well without the ball and consistently hit the open 22-footers.

And finally there is a special group of guards who can do everything: Pete Maravich of New Orleans, Walt Frazier of Cleveland, Earl Monroe of New York and Phil Smith of Golden State.

"Pete is the best," said Houston's John Lucas. "He can do everything. He's not playing with a particularly good team, but he still makes his teammates better. If he ever went with a good team, people would see all the things he can do."