A 21-year-old homeless man was fatally stabbed in the parking lot of a Fairfax County fast-food restaurant late Tuesday, county police said yesterday.

The man, whose name was withheld pending notification of relatives, was stabbed in the upper body. Police found him about 11:40 p.m. outside Arthur Treacher's Fish & Chips in the 9500 block of Lee Highway, near the Fairfax City border. He was taken by ambulance to Inova Fairfax Hospital, where he was later pronounced dead, police said.

Police said the man, an immigrant from El Salvador, was fighting with two other men in the restaurant's parking lot almost two hours after it closed. The man was stabbed several times, said Officer Bethany Funston, a police spokeswoman.

Funston said detectives know of neither a motive nor a suspect in the county's 11th homicide this year. There were 10 slayings in Fairfax in 2004 and in 2003.

She said investigators were "following up on some promising leads." Another spokeswoman said they included an account that the fight was among a group of homeless men who make their camp in the area.

At Arthur Treacher's yesterday afternoon, employees said they knew nothing about the slaying. Customers streamed in and out of the small restaurant, carrying bags of fried seafood in their arms. And traffic rushed past on Lee Highway, unaware that the paved parking lot was a crime scene hours earlier.

Funston said it was not known whether the altercation started in the parking lot or whether it spilled over from one of the nearby establishments, which include a gas station, a convenience store and a high-rise apartment building.

The scene of the slaying is not far from busy Fairfax Circle, where Lee Highway merges into Arlington Boulevard, and a cluster of shops that lines both thoroughfares.