It's 10 o'clock on a Saturday night when Tyrell Biggs strolls into the hotel lobby wearing a sweatsuit, not a mark on his face from the heavyweight fight he won earlier in the day. His 6-foot-4 3/4, 215-pound body molds into the soft couch, his high tops rest on the coffee table.

Tyrell Biggs is totally relaxed.

"When I go back to the hotel, I relax," he said. "I'm back in my room at 8. I'm not out chasing girls. The funny thing is, I can still enjoy myself without taking drugs and drinking.

"I'm probably the only boxer out there who lives clean."

A little more than a year ago, the 1984 Olympic gold medalist never passed up a chance to party and admits he had a cocaine habit that reached deep into his savings. After a buildup of personal problems, fueled by criticism that he "was a heavyweight without a punch" and heckling at his first professional bout against Mike Evans at Madison Square Garden, Biggs said his abuse of cocaine and other drugs reached its limit.

A week before Christmas 1984, he voluntarily checked into the Care Unit Hospital in Orange, Calif. He stayed there four weeks and didn't fight again until April. He talks publicly about his drug problem, the fact that he attends Alcoholics Anonymous as many as six times a week when not training. He also sees a counselor and is subject to "pop" urine tests by his comanagers, Shelly Finkel and Lou Duva.

"He said that telling him not to take drugs was like telling him not to eat," said his publicist, Kathy Duva.

Said Biggs: "The longer you stay away from it, the stronger you are. I went through it once, and that is a goal in itself."

Before he went into the Care Unit Hospital, his trainer, George Benton, had difficulty getting Biggs out of bed in the morning to train. But training now is an obsession, something to keep his mind from partying.

"I wasn't taking boxing too seriously," Biggs said. "I got spoiled by the amateurs. I could pretty much go through the motions. That carried over into the pros. After I went through that, I made a 180-degree turn. I figure now that I'm not doing (drugs) anymore, I should be extraordinary."

In his return bout in April, Biggs surprised many by knocking out Mike Perkins in the first round. Biggs, 25, still is undefeated, knocking out the five opponents before last Saturday's meeting here against James (Quick) Tillis, his toughest foe to date.

Tillis fought Mike Weaver for the title in 1981, and in his career had gone against four other world champions. Biggs didn't knock out Tillis, but he used the left jab well and won a unanimous decision.

"Tillis still had a lot left," Biggs said. "I kind of had to show him what I'm made of. Now I've passed the test, it's time to move up."

Passing the test was important to Biggs, who had been criticized for fighting weak professional opponents. But he still believes that the best road is the long road.

"There is some stiff competition in these next fights," said Biggs, who will go against David Bey on March 9. "The only thing I can say is, I'm still learning."

Another criticism leveled at Biggs is his lack of tenacity in the ring. But his trainers, who have helped change his style since the Olympics, say the victory over Tillis proved otherwise.

"He took the shots pretty well," said Lou Duva. "Don't anyone question the chin of Tyrell Biggs." Said trainer Benton, "In three fights, he'll be as good as any heavyweight."

Under the guidance of Benton, Biggs is using more upper-cuts and punches to the arms and is changing the speed and strength of his blows to keep his opponents off balance. "Now, I know how to throw punches with the weight behind it," he said.

Biggs said in three or four fights he will be ready to challenge for the title. A year ago, he was just happy to get back into the ring.

"I think it's going to take a helluva fighter to beat me," he said. "I think I've learned how to win."