A record Maryland boxing crowd of 19,000 will see Sugar Ray Leonard try to prove tonight at Capital Centre that he is the champion of his neighborhood, against Johnny Gant in a 12-round bout, before he sets his sights on the world welterweight title in the fall.

In addition to those paying from $7.50 to $30 to watch the live action, expected to start at about 10 p.m., fight fans will pay $20 to see a closed-circuit telecast at the D.C. National Guard Armory.

On Sunday, at 3:15 p.m. on WJLA-TV-7, there will be a free treat. Carlos Palomino of Mexico, the World Boxing Council champion, will defend against Wilfredo Benitez of Puerto Rico, in the latter's hometown, the title Leonard and Gant have their eyes on.

The Leonard-Gant bout will be carried tonight by WMAL Radio. The broadcast begins at 9:50. About 2,000 subscribers in Arlington will see the bout in their homes over the Metrocable and Home Box Office cable systems at the regular monthly charges.

The preliminary bouts begin at 8 o'clock.

Leonard, the 1976 Olympic champion, is favored after going unbeaten in 17 professional fights, 10 by knockouts. He is 22 years old.

Gant, 29, has won 44 of 58 bouts, 25 by knockouts, lost 11 and figured in three draws.

Leonard is handled by Angelo Dundee, who severed his managerial ties with Gant after the match with Leonard was scheduled.

In handpicking Leonard's early bouts, Dundee said, "You look to stay away from strength." He apparently considered Gant too tough until now.

"Ray hasn't been hit by a Johnny Gant," said Dundee. "I'm telling you, Johnny Gant is a puncher. I'm sure Ray will win, but I'll be scared every minute."

Jose (Pipino) Cuevas of Mexico is recognized as champion by the World Boxing Association. Leonard is ranked No. 4 contender by that group and Gant not at all.

The WBC rates Leonard No. 10, Gant No. 8. Ring magazine ranks Leonard No. 3, Gant No. 4. In its United States ratings, Ring ranks Leonard No. 1 and Gant No. 2.

Gant had a shot at the WBA title on Oct. 11, 1975, against Angel Espada of Puerto Rico and lost a 15-round decision in Espada's hometown. On Nov. 21, Gant stopped Sammy Ruckard of Spartanburg, S.C., for his fifth straight victory.

Leonard has not boxed more than 10 rounds, going that distance five times. On Dec. 9 he knocked out Armando Muniz of Mexico in the seventh round.

There had been criticism about the quality of Leonard's opponents, but he made an impression when he decisioned Randy Shields of Hollywood, Calif., in October.

Shields was a ranking contender before being stopped by former junior welterweight champion Wilfredo Benitez in August. He decisioned Leonard for the Amateur Athletic Union light-weight title in 1973, Leonard's last loss.

Leonard is maturing into a natural middleweight and looked strong in handling Muniz in his last bout.

Gant has been knocked out three times. Leonard claims he has never been down in 17 pro and 40 amateur bouts.

Gant is quick of hand and foot and likes to control the pace, preferring to try to amass points with a straight left and a sneaky right cross. With his height, 6 feet, he is a stand-up boxer. He is studiously cautious about exposing his anatomy unnecessarily.