There are so many family sitcoms on television these days, it's hard to tell one from another. Viewers tuning in to NBC's new comedy series "Under One Roof" tonight (Channel 4, 9:30) will have no such problem. It's the absolute worst. It's so bad it makes "Family Ties" look like "Masterpiece Theatre."

The show stars Ross Harris as Spencer Winger, a moody teen-ager with corkscrew curls who's supposed to be a cross between Dennis the Menace and Holden Caulfield. His mother Doris, played by Mimi Kennedy, is described as "wacky" -- a sure sign the writers don't have a clue to her character.

Actually, there is something very used about this "new" series. It's really the old "Spencer," a show that premiered in December and was pulled from the schedule shortly after. But that's never stopped Hollywood from trying. Just haul out the old characters, give the plot a lube job and go back to Ma Maison for lunch.

It's difficult to explain the story line. Like "Waiting for Godot," nothing happens.

Tonight's episode opens with the news that Spencer's father has run off with his 23-year-old bookkeeper. (In the production notes she is described as a "19-year-old girlfriend." That shows you how long this turkey has been sitting on the shelf.)

For no apparent reason other than to gloat over the misfortunes of their daughter, Spencer's grandparents move in. Spencer moves to the attic. His grandparents (veteran character actors Harold Gould and Frances Sternhagen) carry on like geriatric nincompoops.

She: "Who's there?"

He: "It's me. Who were you expecting?"

She: "I was expecting you. I was hoping for Robert Redford."

(Big laugh here, thanks to the laugh track.)

He: "If I were Robert Redford, would I be knocking on your door?"

(Adult male snicker track.)

The dialogue is so stale you can see the green mold on the screen. There is much leering and talk of sex and "bimbos."

Spencer has the requisite number of goofy pals, Doris has her circle of friends -- tough cookies with cream centers straight from Central Casting. Doris is presumably trying to heal her broken heart by inviting these hens over for a bridge game. Talking about Doris' errant husband, one of the gals quips, "He must have liked the way she juggled her books," which brings the house down.

The show reaches its predictable crescendo when Spencer -- who probably just picked up his first copy of Psychology Today -- blames himself for his father's absence.

"I'm not what my dad wanted," he pouts. "He wanted the Beaver."

After this half-hour, so do we. Ward, call the boys to dinner.