It may well turn out that "Steps in Time," the new American Dance Machine show that began a month's run at Ford's Theatre last night, will sell out for six months on Broadway, as did its predecessor -- an anthology of production numbers from hit musicals of the past that premiered at Ford's two years ago.

The new show, highlighting couple dances rather than ensembles, may be different in content, emphasis and format, but it also has the prerequisites for popularity -- an easy informality, a cadre of skilled, attractive dancers, and a nostalgic medley of variously peppy, sentimental and sexy showbiz numbers in a diversity of styles.

Yet, for all its genuine energy, know-how and flash, "Steps in Time" appears to me to have an overlay of something strained and flat about it that comes both from the nature of the show and the way it's performed. Most of the material consists of "reproductions" rather than originals, and this isn't easily disguised or compensated for. As the domestic spirits industry has discovered, you can put a certain effervescent liquid into bottles, call it champagne and market it as such. The palate, however, isn't invariably fooled. There's a resemblance, all right, but just enough of one to underscore the distance between the substitute and the real thing.

This is not to say that the American Dance Machine had anything but the noblest objectives in mind. The organization was founded by Lee Theodore in 1975 to preserve and revivify aspects of our vernacular dance heritage that might otherwise pass into oblivion. The question raised by the show is not whether this is a desirable goal, but whether it is achievable in practice.

A large part of the problem is that the thrill of so many of the old show dance routines was so inextricably bound up with the specific dance personalities who created and danced them. Without the charisma of the originators, it's debatable whether the material can survive on its own, in renditions by dancers of another generation and sensibility. "Steps in Time" brings this home pointedly in the few numbers that feature guest artist Francois Szony, an exhibition and club dancer noted for a florid, quasi-balletic "adagio" style with which he has toured internationally for three decades. Szony is the real article, and his dancing of his own routines (with the lovely young Washingtonian, Catherine Caplin, who is his present partner) exudes an authority, spontaneity and magnetism that nothing else in the show can match.

The cast slides briskly through the oddly variegated fare that traverses film and stage musicals, ballroom and cabaret numbers, and idioms ranging from jazz to tap to Latin to Broadway. Among the more memorable items are a Katherine Dunham blues duet, and an elegant but uneven Paul Draper tap creation. The headliners, Janet Eilber and Denny Shearer, are efficient but mechanical, for the most part. A lot more pizazz comes through in the work of some of the other dancers, particularly engaging, sparkly Kathleen Gutrick; silky and distinctively individual John Jones; and the vibrant and versatile Vicki Regan.

An intermission would be a small quick way to enhance the show's appeal -- 90 minutes is a long stretch of sitting, especially on those quaint but none too resilient Ford's chairs.