Just as "All in the Family" begat "Maude," and "The Jeffersons," and "The Mary Tyler Moore Show" begat "Rhoda" and "Lou Grant," now "Alice" has begotten "Flo," and a whole new cast of characters that presumably could reproduce as well.

In this case of video mitosis, the wisecracking head waitress from Mel's Diner, the restaurant where "Alice" works, moves back home to Cowtown, Tex. d

In this premier episode, Flo arrives home ostensibly on her way to a hostessing job in Houston. She takes her mother, sister and old friend to the roadhouse and is persuaded to buy the bar from the owner who is so desperate to sell he keeps lowering the price and accepts her mobile home as collateral. The rest of the action (and presumably the series) is concerned with her difficulties in getting the place open and running.

As situation comedies go, this one is as funny as the form allows. The reason is that its creators make no pretense at duplicating real life; all the characters are Characters with a capital C, larger than life and twice as sassy.

Their excess succeeds (although half an hour is about as much as you could take of comedy this broad) largely because the actors are skilled and the characters intelligently developed to play off each other. Polly Holliday is Flo, and she is endearingly middle-aged, her hair sprayed into a seemingly metallic bouffant arrangement, and she dishs out one-liners like a shcoolboy flipping rubber bands.

The pattern of gags to come are clearly established in the first episode, which airs tonight on Channel 9 at 9:30 p.m. Flo and her prune-faced, prudish sister (played by Lucy Lee Flippen -- who could resist a name like that?) do not get along, and Earl the bartender is a male chauvinist. "He said he'd rather dip sheep than work for a woman," Flo reports.

There's a soulful busboy-piano player, sort of a poet-in-residence, played without a twang by Stephen Keep, and a whole wagonful of other supporting characters.

While it is hard for the average person to begin to understand how network executive decide that one goofy idea for a television show has merit while another doesn't, "Flo" is at least as good as a half dozen other shows that have achieved success. It relies totally on Colorful Characters, but at least these actors attempt to make them believable.