Hatching A Fastback Duckling.

WHILE American auto sales have plunged -- from a peak of 17 million new vehicles just a few years ago to an annual rate of about 10 million -- many carmakers have continued to add to their product offerings, rolling out new models and slicing the existing market into ever-smaller slivers. Consider the new Honda Accord Crosstour, which joins a nascent group of vehicles trying to carve out a niche between conventional sedans and crossover utility vehicles, which are themselves supposed to be more carlike than truck-based, body-on-frame S.U.V.'s. The Crosstour slides into Honda's lineup between the Accord sedan and the Pilot utility vehicle. Other similar new entries are the Toyota Venza, Acura ZDX and BMW 5 Series Gran Turismo. All have a sloping fastback on a slightly oversize crossover body. Any could play the lead if Pixar followed up its movie ''Cars'' with ''The Hatchback of Notre Dame.'' [ABSTRACT FROM PUBLISHER]