Chrysler Corp. and Ford Motor Co. are recalling 6,900 subcompact cars and trucks.

Chrysler said it is recalling 2,000 Dodge Omni and Plymouth Horizon models for repair of fuel tank leaks. Ford announced it is recalling 4,900 trucks to replace potentially defective engine fans.

The 1978 cars were introduced by the No. 3, auto maker only last week in hopes of regaining a dwindling share of the domestic automobile market. The leads stemmed from an assembly line error at the firm's Belvidere, Ill., plant, spokesmen said.

Backseat carpeting in some of the cars was inadvertently stapled through the top of the gas tank, Chrysler said.

"We have determined that approximately 2,000 vehicles may have one of more small holes in the top of the gasoline tank," Chrysler said in a telegram to the National Highway Traffic Safety Administration.

"These holes may allow gasoline to leak when the tank is completely full. They result from an inadvertent departure from the specified assembly procedure."

Chrysler has produced about 25,000 of the subcompacts so far and reported that 2,473 were sold during their first week in dealer showrooms.

Chrysler said the improper procedure "has been corrected in the plant. The affected vehicles have been identified and Chrysler will initiate recall to replace those gasoline tanks which have been perforated.

Ford Motor Co. yesterday recalled 66,000 Mustang II and Pintos to correct defect in the steering coupling. The No. 2 automaker said the recall covers cars built early in the 1974-model year.

"On some of these vehicles, the steering coupling flange that connects the steering gear shaft to the steering column could slip," said Stephen P. Geoffrey, manager of the service engineering office for the Ford parts and service division. The slippage is most likely to occur during parking or other low-speed maneuvers.

Ford said it has received no reports of serious accidents or injuries resulting from the defect.

Ford said the fan blades on some vehicles could crack, causing blade parts to break off.

The company said it had no reports of injuries or accidents from the defect, which involves C-series trucks with FT engines and automatic transmissions.

Ford said dealers will replace the fans at no cost to the owner. Letters notifying owners of the defect will go out soon, the company said.

Ford said it also is recalling 500 trucks in Canada and nine trucks overseas.

And Volkswagen is recalling more than 200,000 1974 through 1976 VW and Audi models to correct what the Transportation Department termed "potentially defective" accelerator cables.

Included in the recall are 1975 and '76 VW Rabbits, and Sciroccos, 1974, and '75 VW Dashers, and 1974 Audi Foxes.

Volkswagen does not know how many of the cars have defective cables which could break, returning the engine to idle, or fail partially, making the throttle stick in the open position.