For those idea of an American musical comedy is "A Chorus Line," where the synchronized kicking serves as an exclamation point to a lot of psychological grousing, "The American Dance Machine," at Ford's Theatre, shows what the term used to mean.

Big dance numbers from shows from the 1940s to '60s have been reproduced and put together into a revue that not only is fun to see, but has something fresh to say about this American art form. When musical comedies attempted less in the way of content, more attention was paid to form. Any simple, optimistic love story could do, if the songs, and dances were strong and the production had a high professional gloss.

In the revue, you can notice that the earlier shows had a frank desire to please and later ones with more sophisticated themes still kept their commitment to being visually appetizing. They are both different from today's style, in which the heavy theme discourages the frivolous.

Thus when "The American Dance Machine" opens with everyone on stage wearing dark sweatshirts and pants, it looks like another '70s show, in which no one is going to pander to any audience love of lavish production. And yet what it goes on to do is to demonstrate how much skill and talent went into creating the pleasure of the big number - it was not, after all, just the costumes, which this show goes on to suggest just enough, with budget petticoats and props.

It is a dance form with an emotional range from high spirits to exuberance and back down to high spirits. Even a dance of mourning, from "Brigadoon," is done in this tradition of indomitable optimism. And the highlight is Harold Cromer, as a hopeful performer only allowed to work the intermission, with his bouyant and successful efforts to "sell" himself through sheer force of pleasurable entertainment.

This is an old theater tradition, and a contrast with the modern style of the narration, to be done each week by a different actress. (Hope Lange is on this week, Tammy Grimes next week, and Chita Rivera the week after.) There, a television-awards-show style takes over, and we hear much too much about the legendary, so and so, and the wonders of everyone's having put this together for us. Musical comedy was never intended to have to get to use through gratitude, and more than the through pity. As its best, it does it just by showing us a bright and happy time.