Trevor Berbick, a 6 1/2-to-1 underdog, got into the trenches with previously unbeaten Pinklon Thomas tonight and gained the World Boxing Council heavyweight championship with a unanimous 12-round decision.

Berbick wore down Thomas with his strength and quickness.

Berbick's victory, before a crowd of about 2,000 in the Riviera ballroom, made him a champion on his second try. He failed to win the WBC title when he lost a 15-round decision to Larry Holmes on April 11, 1981.

There were no knockdowns, but Berbick (31-4-1) was marked around both eyes and Thomas was cut in the corner of his left eye.

Thomas also almost went down in the 11th round when he was put back on his heels by a tremendous left hook to the head. Berbick followed with several hard shots to the head, but Thomas fought back and got out of trouble.

Judges Paul Smith, Spider Bynum and Paul Smith each scored it 115-113 for the 31-year-old Berbick, a native of Jamaica who lives in Miami.

"I was very tempted to bet $25,000 on myself," Berbick said. "But I couldn't because I am a soldier of the cross. I wanted to play with him for the first couple of rounds. I wanted to keep my reserve until it was time to let it loose."

Berbick began letting it loose in the fifth round when both men went at it toe-to-toe, and he took control of the fight over the last six rounds.

Thomas failed in his second defense. He won the title from Tim Witherspoon in August 1984 and knocked out Mike Weaver in the eighth round last June 15. Thomas, who earned $635,000, had new cornermen in co-trainers Bill Prezant and Jeung-Sook Lee. Veteran trainer Angelo Dundee was not working with Thomas because of a reported rift involving the two new men. Thomas is 26-1-1 with 21 knockouts.

By winning, Berbick, who four years ago beat Muhammad Ali in the three-time champion's last bout, earned $50,000 for this fight.