The two stores sell bottled shark fins, the same 12 brands of soy sauce and rice in 50-pound sacks, imported oriental foods that have a limited market in Northern Virginia.

And because both of the small groceries are located along Alexandria's Mount Vernon Avenue, just south of the Arlington border, they are feuding over who should be allowed to serve what is believed to be the most concentrated Thai community in the Washington area.

The grocers' dispute -- scheduled to be heard Wednesday in Alexandria Circuit Court -- illustrates the increasing competitiveness in the thriving ethnic commercial center.

"He wants his customers back," said Moraras Nirapai, the owner of Bangkok 54, the oriental grocery shop on upper Mount Vernon Avenue. "He calls my customers. We had an agreement. He said he wouldn't. If I knew he was opening another place, I may not have bought this one."

Nirapai has claimed in that lawsuit that the man who 16 months ago sold him Bangkok 54 violated the sales contract by opening a competing business six weeks ago.

The $70,000 sale agreement, typical of many such contracts, forbade the seller, Kriengkrai Prathipasen, to open another oriental food shop in the same area, according to the suit.

Prathipasen, who was interviewed at SukhoThai, the Thai grocery on lower Mount Vernon Avenue, denied violating the contract. "It is not my business," he said this week as he stood near 150 bottles of soy sauce in the store. "It belongs to my ex-wife."

The store's business license names his wife, Petcharee Prathipasen, as the proprietor. Court records show she divorced Krienghkrai Prathipasen in 1981.

"She lives with my brother now," Krienghkrai Prathipasen said. "I just help them once in a while . . . . I haven't done anything wrong."

His Thai competitor who sells the same brands of soy sauce and imported videocassettes from the Southeast Asia 10 blocks away, insisted Prathipasen has violated at least the intent of the legal contract.

"He's really behind the business," Nirapai said. " . . . When we bought the place we paid for his customers. Now he's taking them back -- he's calling them up and lowering his prices. Already our business is hurt."

Pakee Suthamchai, an employe at Bangkok 54, said Prathipasen has come into the store and told people about the new shop. "He sat there," Suthamchai said pointing to a pile of yellowed Thai newspapers, "and told people he opened a new store. We were so upset. Mad. But what could we do?"

Prathipasen, like Nirapai a native of Bangkok, scoffed at the idea that two grocery stores could not survive in an area that is home to an estimated 450 Thai immigrants and 3,000 other Asians, including Vietnamese, Koreans, Cambodians and Laotians. He talks about American capitalism.

City officials say the competition between the two stores has intensified as the neighborhood, targeted for redevelopment, has bloomed.

"There has been a lot of change since 1981-82," said Marianne Tillotson, the city's commercial revitalization coordinator. "A train used to run down the avenue and it was full of older developments. Now it's got . . . the best place to clean oriental rugs, the best place to buy hot chili, the best Creole restaurant."

Since 1981, Alexandria has spent $280,000 polishing what is called the Mount Vernon Avenue Corridor, adding uniform street signs with a rainbow logo, Victorian-style wrought-iron benches, wooden trash bins and brick sidewalks.

Last year, $240,000 in public and private loan subsidies helped small businessmen refurbish shabby buildings, and in the proposed 1987 budget, City Manager Vola Lawson calls the Mount Vernon Avenue Corridor a top priority and requests $575,000 for it.

Though there are no figures pinpointing the number of businesses owned by immigrants, city officials say they are steadily increasing and estimate that between 10 and 15 percent of the 240 businesses along the corridor are now run by foreign-born residents. The number of immigrants in the area is also difficult to obtain, because the last census was taken in 1980, before the recent wave that brought many to Alexandria.

"There has been a lot of turnover in the past 10 years," said Jack Powers, executive director of the city's Economic Opportunities Division. For instance, he said, "The Blue Fox corner bar has become Los Amigos a Tex-Mex restaurant ."

The upgrading of the Mount Vernon area, which encompasses much of Arlandria West, has begun to force some of the immigrants to outlying areas, such as Manassas and Woodbridge, according to Kim Cook, director of Project Bridge, a pilot Northern Virginia immigrant and refugee program funded by the federal government. For those who want to stay, she said, rising rents have meant fiercer competition for apartments, jobs and businesses