David Soul trying to look thoughtful is like Orson Welles attempting to slip gingerly into a seat on the Eastern Shuttle. It defies the laws of nature. Why does Soul get so many TV movie roles? He can't even look soulful. When it comes to simulating human emotions, he is the consummate ersatz.

"Homeward Bound," the CBS movie at 9 tonight on Channel 9, would be groggy and morose enough without Soul's slovenly, hangdog sulk, but with Soul in a key role, the movie turns into a warm glass of milk and quickly curdles. Actors who star in a series like "Starsky and Hutch" that calls more for driving ability than acting ability ought to become cabbies or truckies once the series end, but Soul appears in movie after movie on the air.

This time he plays the father of a 14-year-old boy who is dying of TV cancer, the kind that only people on TV die from. This form doesn't affect the appearance, never becomes unseemly, produces only mild fatigue or, in this case, one bout of vomiting in a men's room. Dad is divorced, and for a month's custody of his son, the doomed teen asks to go visit ornery, cranky old grandpa at his winery in Northern California.

That gives an excuse for a picturesque drive up coastal Route 1, but how we will suffer for this fleeting pleasure! Dad and granddad hate one another with a passion, or a half-passion, and this leads to some potent dramatic colloquies:

Gramps: "You're a chicken."

Dad: "You're a fool."

Son: "Why don't you two just shut up?"

Writer Burt Prelutsky must be trying to pull the public leg with this angst-ridden pastiche, a feckless cross between Bad o'Neill and Bad Steinbeck translated into the flat vocabulary of the TV movie. It's hard to believe Prelutsky ever expected us to believe that his dumpy, leaden hero once aspired to being "another Hemingway," especially when he sashays up to women in bars to ask, "Have you ever been through analysis?"

That the guy writes TV commercials is supposed to constitute the ultimate sellout. But it could have been worse. He could have been a writer of TV movies.

Moosie Drier, seasoned veteran of the ABC Afterschool Specials, plays the stricken lad with as much forbearance as possible. Michelle Downey, as the pretty girl he literally finds up a tree, makes a welcome, attractive distraction. And Barnard Hughes generously flatters the poorly written role of grandpa.

But the director, Richard Michaels, failed to give Prelutsky's comatose script the breath of life it needed. Reconciliation between gramps and dad has no impact when it finally, inevitably, arrives, and every time Soul goes into one of his pouts over what-could-have-been, you want to scream, at the very least, bloody murder. Maybe David could get a job as Dan Rather's chauffeur; it would be a more honest way to make a living.