L.P. Steuart, Inc., the oldest and once the largest Chrysler-Plymouth dealer in the Washington area, has sold one of its dealerships and abruptly closed the other.

The Steuart family also sold its interest in two local taxi groups with which it was long associated, Eastern Cab Assn. and Imperial Cab Assn.

The L.P. Steuart dealership on East-West Highway in Silver Spring was closed Monday, a move that Chrsler regional officials said surprised even them.

A Chrysler spokesman said the company would take over the lease on the building and the dealership would reopen soon. Since Steuart shut down, a number of local dealers have bid for the franchise, he said.

Ed Dempsey, manager of the dealership, said the owners decided, after 40 years at the location, that "with the losses over the past three years, it was better to close it down and lease the building".

He said customers' cars that were in for repairs would be fixed and returned to them as soon as possible. The inventory of new and used cars will be wholesaled or returned to Chrysler.

Steuart's other location at 34th Street and Benning Road, N.E., was sold effective Nov. 1 to Monroe Lenoff, who changed its name to Monroe Chrysler-Plymouth. Lenoff also owns Monroe's Automotive Center on West Virginia Avenue, which he purchased in 1972 from other Steuart interests.

The Steuart Chrysler-Plymouth operations are now owned by Harry Martens, a son-in-law of the late L.P. Steuart. Neither Martens nor his son could be reached for comment yesterday.

L.P. Steuart had a third location, in downtown Washington, but that closed in 1974.

The Martens also owned Central Warehouse Distributers, the Chrysler Corp. parts dealer for a region from Richmond to Philadelphia, as well as Martens Chevrolet and Datsun and Volvo dealerships in the Washington area.

The deversification into other auto brands reportedly had strained relations between Chrysler and the Martens, who believed they could be more successfull with other makers.

An official of Chrysler, which recently has lost market share to Ford and General Motors, said Lenoff had already increased sales subtantially at the dealership he took over. The Washington region reportedly is Chrysler's largest.

The Imperial and Eastern Cab operations, which were among the largest buyers of Chrysler cars, were transferred to Daniel Smith and his son, of other taxi operations, including American Fleet, City Cab. Anacostia, Albert and James, who own a number Bell, Cholly Cherry and Barwood-D.C.

Washington, taxi associations act as umbrellas for drivers, who buy or lease their cars from the associations, and depend on them for services such as maintenance, financing, insurance, advertising and radio contacts.