Take Route 66 straight through Peyton Place, continue on past Knots Landing, Dallas, Somerset and Pine Valley, make a left turn at God's Little Acre, a right at King's Row, follow the Hollywood Freeway to the Sunset Boulevard off-ramp and there you are -- Puberty Junction, setting for as much diddling, fiddling, twiddling and jimmy-jo as every you sunk your eyes into.

Officially, though, it's known as Midland Heights in "Secrets of Midland Heights," the new CBS teen-age sexus maxiums that premieres at 10 tonight on Channel 9. Lee Rich, whose Lorimar Productions gave the world "Dallas," thinks he's found the perfect formula for another steamy-steamy serial -- lots of lusty kids feeling their way toward adulthood in a town rife with moral corruption and political intrigue.

It deserves among the highest accolades that can be lavished on pandering and prurient television slop: Yum yum yummy yum yum!

In fact, "Midland Heights," though it has nothing to do with anything resembling life, is not badly acted, is attractively put together and does succeed at the paltry level it wants to. Many of the kids in the cast are engaging and earnest and some day may get a chance to play actual characters in a real drama.

And as for the adults, venerable Martha Scott sums them up, and captures the essence of the series, when as a wealthy and powerful matriarch she philosophizes in the premiere, "'Gauche' doesn't bother me."

"I'm a virgin," confesses a desirable young sprite to a breathless young man. "But -- and this is a very big 'but' -- I'm tired of being innocent, and I want to give it up." A few scenes later and they're off on a hayride. "This is a night of firsts, isn't it?" she says.

"Why me?" he asks. "Why not you?" she asks. "Why put off till tomorrow what you can do tonight?"

But these well-laid pland do quickly go awry when our young woman and her young man arrive at the Granary Cabins motel and see a familiar roadster. "That looks like my father's car," says the lad. "He must be in Number 19!" Yes he IS! A with the girl's own MOTHER!

And what a bucket of cold water that is!

Now what kind of a bottomless pit is this Midland Heights? It's a quiet town -- until the lights go out -- and the kind of place where the hayrides may be lascivious in nature but the kids still sing old chestnust like "Tom Dooley" and "Michael, Row the Boat Ashore." Oh, brother.

And one other thing about Midland Heights. There's a black person living there. Just one, or so it seems. She's a nurse at the local hospital. When hunky-clunky football star Burt Carroll (Lorenzo Lamas) is confined to a bed there and makes a lateral pass at the nurse, she says no thanks, she's afraid she'd lose her job.

When he complains about the brusque way she ascertains his temperature, she says, "You're lucky I took it in your mouth."

As on "Dallas," and predictably enough, a central figure in the continuing story is a Machiavellian manipulator, in this case not J. R. Ewing but "Uncle Guy" (Jordan Christopher), such a dastardly cuss that he opens and reads his niece's diary and has her boyfriend railroaded out of town, albeit in a Volkswagen. He thinks the girl might come between him and his inheritance and besides, he just wants to be mean.

Among the youngsters, the most appealing, intelligent and agreeably spunky is Holly Wheeler -- the good-humored virgin on the hayride -- played by Linda Grovenor. It only makes an insane kind of sense, then, that CBS has announced the following: "Linda Grovenor, who plays Holly Wheeler in the series premiere, has since been replaced in that role by Marylin Jones. Miss Jones will portray Holly in all subsequent episodes." m

When it comes to sheer wickedness, Midland Heights has nothing on Television City.