A 43-year-old Arlington man who stopped at a Gainesville, Va., grocery store to buy soda was shot and killed yesterday morning after an argument outside the store with a man armed with two handguns, Prince William County police said.

A 27-year-old Sterling, Va., man was arrested shortly after the shooting and charged with first-degree murder, police said.

Investigator Henry Wood of the Prince William County Police Department said the men apparently did not know each other, and a motive for the shooting was unclear.

Wood said Calan R. Derden of the 3600 block of North 22nd Street, Arlington, was on his way to visit friends in Gainesville when he and a female companion stopped at Phil's Market, a small grocery store at 14112 Lee Hwy., a few miles west of Manassas, about 10 a.m.

While in the store, Derden became involved in a dispute with a man who was carrying a .357 magnum in a shoulder holster and a .44 magnum handgun in a hip holster, Wood said.

The men left the store, and the argument, which Wood said included threats by both men, continued in the store's front parking lot, according to the officer.

"I think Derden was ordered out of the store, or at least he the gunman called him out," he said.

While outside, the gunman pulled the .357 caliber weapon from his shoulder holster and fired once, striking Derden in the left side of the chest near his rib cage, according to Wood.

Derden was taken to Prince William County Hospital where he died a short time later. Derden's companion, a 30-year-old Falls Church woman whom police declined to identify, was not wounded.

A short time later, police arrested Thomas Cumberland of 200 North Emory Dr. in Sterling. Cumberland, who told police he was employed as an elevator installer in Northwest Washington, was being held in the county jail without bond last night pending a hearing.

Wood said that Cumberland had been seen carrying two holstered weapons "cowboy style" before yesterday's shooting, and that area residents had complained about Cumberland to the Loudoun County Sheriff's Department in the past.

Wood said that it was not illegal for a person to carry holstered weapons, and the complaints about Cumberland stemmed from residents who were frightened by the sight of the weapons.

"It's hunting season," he said. "It's not unusual to see someone dressed as a hunter, but it's usually a shotgun they are carrying. It's legal to carry a handgun as long as you don't whip it out of the holster and brandish it," he said.