Sugar Ray Leonard showed Johnny Gant who was the boss of their neigh-borhood last night before a record Maryland boxing crowd of 19,743 at Capital Centre.

He finished off Gant with sudden fury after 2 minutes 57 seconds of the eighth round, when referee Joe Bunsa halted the welterweight bout to spare Gant further punishment.

Leonard's flashing right hand knocked down Gant 15 seconds before the end of the round in the midst of an exchange inside when, for some reason, Gant came down from his erect, jabbing stance and bent down from his 6 feet of height and began mixing it inside.

Gant took the mandatory eight-count and then Bunsa asked him if he was all right. When he nodded assent, Bunsa reported, he saw Gant's gaze was Glazed with uncertainty.

He permitted Gant to continue, but Leonard swooped in with about four savage punches, lefts and rights to the head and the referee intervened.

"Gant did not complain when I did," Bunsa said. "He might have gotten hurt if I had not halted it."

It goes into the books as a techbnical knockout in the eighth.

Leonard was ahead on all three officials' cards through the first seven rounds. Referee Bunsa scored it 34-31 and so did judge Larry Barrett. Judge Terry Moore had it a 35-28 sweep under the five-point-must system.

Moore did not give Gant a round. Bunsa gave him the fifth and called the fourth and sixth even. Barrett gave Gant the seventh and had the first and sixth even.

It was unbeaten, undrawn Leonard's 18th victory, 11th by knockout.

Gant failed to finish for the fourth time in losing his 12th bout against 44 victories.

Gant, 29, bothered Leonard 22, for several rounds. He succeeded in holding off Leonard with long jabs and occasionally snapped right leads to break the combinations leonard attempted to put in motion.

Leonard was spoiling for a slugging match from the outset, so much so that he became impatient with Gant's cautious style and missed badly with right chops to the head.

Gant tired a bit at the end of the fourth round, but before the bell for the fifth his corner shouted, "Go with a right hand."

It worked. Gant surprised Leonard with three straight right crosses to the head.Yet, just before the roundending bell, Leonard unloaded with an overhand right that made Gant clinch.

As if Leonard had lured Gant into opening up a bit in the fifth round, manager Angelo Dundee gave Leonard a pat on the rear leaving his corner for the sixth, suggesting, "Now's the time to go get him."

But once more, Gant kept Leonard from getting close enough with his punches from a side-to-side bit of bobbing and weaving.

Leonard got another significant signal before the seventh round when an ice pack was applied to his right eye. Although there was no visible damage, he began stalking Gant with more disdain for the veteran's snaky jab.

Gant got a similar hint before the eighth round, when his left eye was dressed with grease as a precaution. Either he suddenly ran out of gas or he was beginning to feel a cumulative effect from stronger Leonard's punches.

In any case, he bent down his rangy frame and chose to swap shots inside with an deviously eager Leonard.

A glancing, but whipping, one-two combination upset Gant's poise and he tried to hide it in a desperate clutch.

Then Leonard displayed the killer instinct of a prospective champion. He landed with a left swing and a right swing to the head; caught Gant with a head-snapping uppercut.

Gant faced up to his predicament and gambied for a lucky punch. But his speed of hand and his previously husbanded energy were spent.

Leonard clubbed him with two sizzling rights to the jaw and when he tried to claw at Leonard to clinch, the 1976 Olympian dropped him with a short right in his own corned before Bunsa took his merciful action.

At 146 to Gant's 144 3/4, Leonard looked several pounds heavier, and stronger at that juncture.

Gant's solace was that he earned a flat guarantee of $25,000 from the Capital Centre gross gate of $300,000-plus and a percentage from the closed-circuit television showing at the D.C. National Guard Armory. Leonard had a guarantee of $25,000 and, after expenses, split with Capital Centre, 50-50.