Just one more small thing Americans and Europeans don't quite agree on: General Motors X cars. Americans love them.Europeans don't.

European sales have bombed while GM has had all three U.S. plants -- Ypsilanti, outside Detroit; Tarrytown, N.Y.; and Oklahoma City -- working two shifts a day since April 1979, making the redesigned, front-wheel-drive cars.

U.S. sales have been good to torrid, but the Europeans turn their thumbs down. Or nose up. The two-shift operation of those plants is in stark contrast to other American automobile assembly operations.

When GM began making the all-new vehicles, the corporation shipped 10,000 to Belgium, aimed at the Swiss, German and Benelux markets. They were not a big hit. In fact, GM has just now finished reconditioning and selling 725 cars that were shipped back for lack of interest there.

The reconditioning included filling catalytic convertors with chemically treated pellets and changing seat belts, headlamps, and in some cases even brake linings. The bulk of those returned were Chevrolet Citations. But some Pontiac Phoenix, Oldsmobile Omega and Buick Skylark models also took the boat back this way.

According to GM overseas spokesman John Maciarz, all 725 cars have now been sold to fleets after being reconditioned for the United States at GM's Baltimore plant.

Maciarz said the market got soft in Europe just when the first GM European-type cars arrived there. He said it was the primary reason for the trans-Atlantic shuffle. GM refuses to divulge any of the costs involved in the ship-there, ship-back operation, but an educated guess would be somewhere between $300 and $600 per vehicle.

Both the National Highway Traffic Safety Administration and the Environmental Protection Agency approved the move, Maciarz says. Buyers also were told of the complete shipping shuffle and signed disclosure notices about the cars having been shipped to and from Europe.