There are only two reasons for making a trade. One is to bring in somebody you want. The other is to get rid of somebody you don't want.

The recent Golden State-Houston basketball trade was a bonanza in that it accomplished both objectives. Golden State freed itself of Joe Barry Carroll, described by one NBA general manager as "a thoroughly miserable person," and acquired the unrealized Ralph Sampson. Houston was inclined to show Sampson the door, and overjoyed to welcome Sleepy Floyd, even if it had to take "Joe Barely" as well.

Because of the salary cap, you rarely see blockbuster trades anymore involving stars rather than draft picks. The last one exchanged Jeff Ruland and Moses Malone in 1986. Before that? Phoenix sending Paul Westphal to Seattle for Dennis Johnson in 1980, a trade that quickly diminished both teams. Before that? Probably, Milwaukee accommodating Kareem Abdul-Jabbar's wish to move on in 1975 by trading him to the Lakers for four players who became Bucks starters.

A trade like this is not only rare because it involves all-stars, but rarer still because it involves the most precious commodity in the NBA: centers. Like solar eclipses, such portentious trades deserve study.

This one gives Ralph Sampson an opportunity to reverse the downward slant of his career and grasp the greatness so many have predicted for him.

And it gives Houston the cards to shoot the moon.

Two seasons ago, after they upset the Lakers in the conference finals, the Rockets were one outstanding guard away from the NBA title.

Floyd is that guard.

He averaged 18.8 points and 10.3 assists last season. If you wondered how he might perform in a big game -- since Golden State rarely played any -- he pumped 51 points into the Lakers in one playoff game, a record 29 in one quarter. He can run. He can pass. He can score. Perhaps most important to the rudderless Rockets, he can lead.

The Rockets are suddenly a very explosive team. They already have the best center in basketball, Akeem Olajuwon. Now that the Twin Towers concept has been razed, Olajuwon can play unimpeded around the basket. The versatile Rodney McCray, once the third pick in the draft, will also have more work space without Sampson, since the likely power forward, little known but highly coveted Jim Petersen, is a standard-issue banger -- not a 7-foot-4 Hamlet prone to taking 25-footers in defiance of not having been born a foot shorter.

At guard, the Rockets were burdened with role players being asked to log too many minutes. Floyd's presence suddenly sharpens those roles. With Floyd comfortable at point and shooting guard, the pressure is off Allen Leavell to be a full-time player. And with defenses having to concentrate on Floyd, aging gunners Purvis Short (lifetime 19.4 points per game) and World B. Free (21.2) will find it easier to load up.

If the Rockets don't turn right around and deal him, Carroll can be all gravy for them. True, he has a very soft, uninspired game. But let's not mistake Sampson for Mike Tyson. Over their last four NBA seasons, Carroll's numbers (36 minutes, 21.8 points, 8.1 rebounds) approximate Sampson's (35 minutes, 19.9 points, 10.5 rebounds). Carroll is a big-time NBA center. With a Dale Carnegie diploma, half the clubs in the league would tumble for him. Where Sampson restricted Olajuwon's movement, Carroll will free him to play some power forward. If Carroll's attitude hasn't poisoned the well, he could do for the Rockets what Mychal Thompson does for the Lakers and Bill Walton did for the Celtics. If not, he can fetch a power forward and a backup point guard.

Sometimes a change of scenery is all that's needed to steer a player to a better course. Lenny Wilkens called Dennis Johnson "a cancer" in Seattle, but they love him in Boston. In 1980, Robert Parish was unhappy and not playing to his potential with Golden State. The Celtics made the Trade of the Decade, swapping the No. 1 pick in the draft to Golden State for Parish and the No. 3 pick, with which they selected Kevin McHale. Parish thrived in Boston, where his first coach was Bill Fitch. Maybe Fitch will be twice lucky with Carroll, who, ironically, was that Warriors' No. 1 pick.

Perhaps new surroundings will shake the enigmatic Sampson loose from his deep sleep. How puzzling Sampson is. So much talent and so little spark. Has there ever been such a potentially devastating player? Coaches cower in fear of what he might wreak on the court. Yet so often he's an illusion, a ghost you can't see. To be great you have to be there every night. Sampson regularly plays by rote, like he's 1,000 miles away.

The Warriors told Sampson he's the rock they'll build their franchise on, and he told them he wants to play center. In the past he has rebelled against using his height in its natural setting, and insisted on showcasing himself, like a spoiled debutante, at small forward and guard. Coaches have indulged him by allowing him to decide where and when to express his talent. The result has been an unsatisfying, self-serving work in progress. He must be made to understand the responsibility great talent imposes.

Only once in the 1980s have the Warriors made the playoffs. Golden State has been a sinkhole for a decade. Players disappear, or worse, end up in drug or alcohol rehabilitation. John Lucas, Micheal Ray Richardson, Chris Washburn and Chris Mullin have come undone in the Bay Area. In his first year at the executive helm Don Nelson is bailing water furiously. His history says he'll reach dry land. Should Sampson commit himself to the task, they'll get there that much sooner.