International Harvest Co. is recalling more than 20,000 heavy trucks to replace unsafe front axle aluminum wheel hubs, the National Highway Traffic Safety Administration announced yesterday.

The company will replace the aluminum hubs on 1975 through 1977 model Transtar, Cargostar, CONCO, Fleetstar, Loadstar and S-Series trucks.

Agency administrator Joan Claybrook said oil leaks on wheel rims or tires are a possible sign of this problem.

"A failure will probably be accompanied by noise, wheel vibration and difficulty in steering," she said. "Failure to heed these warning signs could result in loss of a wheel and a dangerous crash situation."

No accidents have resulted from this defect, the agency said.

International Harvest will send notification letters to owners about Nov. 15. Replacement parts will be available at dealers Dec. 15.

The safety agency also announced it has begun an investigation into possible automatic transmission problems with 2 million 1973 through 1978 Ford. Mercury and Lincoln passenger cars.

"When the shift lever is placed in the park position vibration from a running engine or a slammed door can cause the transmission to jump into reverse gear," the agency said. "If the driver has left the vehicle, it could move backward by itself, causing accident, injuries or property damage."

Involved in the investigation are models with automatic shift levers mounted on the steerinf column and which have 351-cubic-inch and larger engines.

The agency said there have been a total 31 owner complaints about this problem, involving one death and 14 injuries.

Ford Motor Co. also announced that it is recalling about 1,900 of its 1978 Econoline vans and club wagons in the U.S. for safety defects.

The company said the adjusting sleeve clamps on some of the vechicles could break, separating the tie-rod adjusting sleeve resulting in a loss of steering control.

No accidents or injuries involving these parts have been reported, Ford said.

The company also is recalling 135 units in Canada and 10 in export markets because of the problem.

Mercedes-Benz of North America the importer of the German-built luxury cars, is recalling 419 of its 1977 model 6.9 sedans to replace the ignition distributor.

A Mercedes spokesman said the distributors involved do not meet the emission control specifications submitted to the federal Environmental Protection Agency.