Undefeated Marvis Frazier, a son of former heavyweight champion Joe Frazier, stopped Guy Casale after four rounds of their scheduled eight-round heavyweight bout tonight. The fight was a preliminary to the Sugar Ray Leonard-Tommy Hearns welterweight bout and marked Frazier's sixth straight victory.

The ring physician awarded the technical knockout when he found that Casale's nose had been broken during the fourth round. Casale was not permitted to answer the bell for round five.

Frazier hurt Casale, a native of Newark, N.J., with combinations in the third round, causing swelling around his eyes and a slight cut on his nose. Late in the fourth round, Frazier buckled Casale's legs with a sharp right to the head just before the bell. Casale is 15-3-3.

Unbeaten Edwin Rosario, preparing for a junior lightweight title fight, scored his 20th consecutive victory with a unanimous 10-round decision over James Martinez. Rosario was nearly perfect on the judges' cards, winning by 100-90, 99-91 and 99-91.

But Rosario, ranked third in the world, failed to keep his knockout record perfect. He had knocked out all 19 previous opponents, but tonight never really had Martinez in trouble.

In other bouts, unbeaten heavyweight Tony Tucker of Detroit recorded his 10th straight victory, all by knockouts, by stopping veteran Harvey Steichen of Carson City, Nev., in the third round.

Jesse Prieto of Las Vegas survived a knockdown and two badly cut eyes to earn a draw with Ricky Bunch of Moline, Ill., in a four-round heavyweight fight.