Just as the British and French are discussing grounding their expensive supersonic Concorde airliners, an American entrepreneur -- with a capital E -- is negotiating to use two of them for his all-package airline.

Frederick W. Smith, the fast-paced American businessman who heads the enormously successful Federal Express, an overnight all-package air freight service, wants to use two Concordes to carry packages across the Atlantic, promising next-day delivery.

Smith has been talking with the British and French governments for a couple of months with the idea of leasing two Concordes, with the possibility of using a third as backup, for the service.

According to Federal Express officials, the transatlantic service would operate from a U.S. airport -- either Washington's Dulles International, Newark or New York's JFK -- to Shannon, Ireland, or Prestwick, Scotland. There, Federal Express would set up its central sorting facility, patterned generally after its central U.S. facility in Memphis. Packages would be sorted at the European airport and then put on smaller planes to be delivered to their destinations. Smaller planes also would pick up packages at pick-up points throughout Europe and take them to Shannon or Prestwick for placement on a U.S.-bound Concorde.

According to Federal Express official William Carroll, Dulles and Shannon look like best bets for the service. Because of the six-hour time difference, a Concorde could leave Europe laden with packages at 9 p.m. and arrive here by 10 p.m.; here, parcels would be put on a Boeing 727 to Memphis, be fed into Federal Express' system and be delivered in the routine way, he said. Going to Europe, the plane would leave Washington at 9 p.m. and arrive in Europe by 9 a.m.

Although the Concorde's high operating expenses and mounting losses have caused the French to consider suspending its Concorde passenger operations -- the French are talking with the British about it now -- Smith maintains that Federal Express can make money using them. Although the passenger service can accommodate just 100 persons, Smith says the Concorde could accommodate an awful lot of packages if made into an all-cargo plane.