Two men were fatally shot in separate incidents in the District yesterday by assailants who brazenly walked into businesses during busy daytime hours and gunned down their victims in front of witnesses.

Frank Gibson, 32, was killed about 10:40 a.m. in a confrontation with a robber in the Hudson Trail Outfitters Ltd. store in the 4700 block of Wisconsin Avenue NW where he was the general manager.

About five hours later, Andre Reese Jr., 18, was in one of the barber chairs at Troyit's Barber Shop in the 2400 block of Martin Luther King Avenue SE when two gunmen burst in.

Seeming to pick Reese out from among three barbers and at least one other customer, they opened fire, pumping bullets into Reese's head and torso.

It seemed to be an execution-style killing. "They definitely didn't want him to do any talking," one police official said.

The earlier shooting on a commercial strip in well-to-do Tenleytown shocked nearby residents and business owners, who said the area has seen an increasing number of burglaries, robberies and other crimes in recent weeks.

By midafternoon yesterday, when word spread that Gibson had died from the gunshot wound, co-workers were still collecting bits of information, reconstructing the attack. One said the gunman passed a note, and Gibson's only comment from behind the counter was, "What?"

Homicide investigators said there were signs of a struggle. But the broken glass on the counter, said one store employee, may have been caused by the paramedics. The only thing clear is that two Patagonia storm jackets, each worth $300, were missing.

Two employees and several customers were in the store at the time, but none was close enough to witness the confrontation from the beginning, said one investigator. Susan Strain, the comptroller for the 13-store chain, said Gibson apparently helped the man select the jackets, and then went behind the counter.

Gibson rang up the sale, and at that point the man made his demand. "Evidently," said Strain, "the individual pulled a gun and demanded money, and Frank resisted and he was shot."

Gibson, who was married and the father of a toddler, was shot in the abdomen. The gunman fled and ran north on Wisconsin Avenue, where a passing police officer spotted him and gave chase. The man headed east on Albemarle Street and jumped into a waiting Ford Escort. The car, with District tags and driven by another man, sped off.

Gibson was taken to Georgetown University Medical Center, where he died at 1:13 p.m.

Strain said Gibson, of the 4000 block of Pinebrook Road in Alexandria, joined the chain three years ago and recently moved from a Virginia store to the one in Northwest, where he was the general manager. He was strong-willed, even "ornery," and not the type to take abuse, she said. He is survived by his wife, Patricia, and son, Kyle.

He was "an all-around good guy," said Strain. "He was a real strong leader for the people here . . . a good force."

The shooting death of Gibson marked the second killing during a robbery attempt in the city in a week. On Tuesday night, Clarine Collier-Wilson, 28, was stabbed to death in front of her two daughters by a man who demanded money on a street in Adams-Morgan. So far this year, about 55 of the District's 443 homicides have occurred during robberies or robbery attempts, police said.

The Tenleytown commercial strip has had a recent wave of crime. On Thursday night, an armed man robbed the Joanne Hallmark Shop, three doors from Hudson Trail Outfitters. A camera store on the block also was robbed recently by a man who took money collected for a Lion's Club fund-raising effort, merchants said.

In the card shop robbery, owner Marlene Luber said the gunman got away with less than $200. That holdup and the one yesterday are not related. Luber said the man who held up her shop was white, and police said yesterday's suspect was black, as was his companion in the car.

Police said the gunman in yesterday's shooting in Tenleytown is about 6 feet tall, weighs about 160 pounds, and was wearing a green military-style jacket and a green baseball cap. He was carrying a brown shopping bag.

They asked anyone with information to call the homicide division at 202-727-4347, or the Crimesolvers hot line at 1-800-673-2777.