Washington, D.C., middleweight Simon Brown, who had lost his first bout last November to Marlon Starling, stopped Kevin Howard in seven rounds last night to highlight a busy card at the Washington Convention Center.

Two other District professional boxers, cruiserweight Boone Pultz and welterweight Maurice Blocker, remained undefeated in their 10-round, nontitle bouts.

Hector Frazier, son of former heavyweight champion Joe Frazier, didn't fare as well, losing by TKO.

Brown (22-1, 16 knockouts) wore down his opponent in the third round, landing combinations to Howard's head and body. Howard defended himself until the sixth, when Brown consistently connected with right overheads and left hooks to his face.

Brown fueled excitement for the next round, punching after the bell sounded. Howard immediately moved his face close to Brown, and the boxers had to be held back.

"I went back to the corner," said Brown, "and tried to listen to everything. What I needed to do was to try to throw the combination."

Said Jose Correa, Brown's trainer, "I said, 'he's trying to go for broke. Stay relaxed.' "

Midway through the seventh round, Brown's hard right cross had Howard falling back against ropes. Brown kept after Howard, and the referee stopped the fight.

"He's a good fighter," said Brown. "My skill was just a little better than his."

Pultz, who improved his record to 13-0 with nine knockouts and one no-contest, went after Alvino Manson with vigor in the fifth round with a series of combinations and a left hook that stunned Manson. After another flurry, he followed with a clean right cross.

Manson fell suddenly in the seventh. It came as the two were exchanging body punches. Pultz slipped in a short left hook, and, after hitting the canvas, it took Manson three minutes to stand. He was taken to Howard University for routine observation and was "doing fine," said his trainer Henry Orr.

"I thought he was a tough, hungry opponent," said Pultz. "I tell you, I haven't hurt anyone in three or four fights. It was good to see it's still there."

In a mundane fight, Blocker won a unanimous decision over Leland Hart of Atlanta. Blocker used his left jab well to improve his record to 22-0. Hart did a good job of blocking many punches. "He was really strong," said Blocker. "I didn't get frustrated,though. I'm undefeated. No matter how I win it, I'm happy.

"Because of him getting low, I maintained him with the jab. Use the jab and everything follows."

Said Hart: "He just fought a smart fight by keeping his jab going. After a while, I got to feeling good and got the drive going. I was stiff at first, but by the time I caught up, he was going."

Tyrone McKelvy of Washington won a split decision over Floyd Simmons of Baltimore.

James Sudberry of Hamilton, Ohio, earned his technical knockout over Frazier when the elder Frazier threw in a towel 1:29 into the fourth round. Jeff Nance won a unanimous decision over William Lucas and Larry Pringle of Washington ended his bout with Don Parker in a draw.