"Lou Grant" is the best now TV show of the season. Like the man in the title, it is a bracing, reassuring combination of an essentially gentle spirit and good, old-fashioned guts. This may be not only what television needs, but what America needs.

Certainly ther's not a prime-time network entertainment series more intelligently crafted or more demonstrably concerned with human nature. Grant, as played with bluster and sensitivity by Edward Asner, could be the first major character in TV history to walk out of a comedy series ("The Mary Tyler Moore Show") and into a dramatic one. The transition is smooth.

There are laughs (though no laugh track) on the premiere, at 10 o'clock tonight on CBS (Channel 9), and pretty rich ones at that. But it's a serious, thoughtful show, and as we remeet Grant, we find him going through one of the loneliest and most unnerving of passages - out of work and droped into a town, Los Angeles, that he once knew but that no longer knows him.

"I'm 50 years old and I have $280 in the bank," he mopes. He's also lost 40 pounds - as has Asner - but people keep telling him, "I liked you better fat."

The creators of this MTM production - writer Leon Takatyan, director Gene Reynolds, producers James L. Broooks and Allan Burns - hit the right tone right off, and early shots of Grant arriving at L.A. airport, his rumpled countenance silhouetted against glass doors leading to the glare outside, set us up for a moving, engrossing hour.

Grant goes to see an old pal at the Los Angeles Tribune (the Los Angeles Times was the principal model for this fictitious daily) and is offered the job of city editor, so long as he can win the approval of the wealthy, feisty woman publisher, played by Nancy Marchand. Their first meeting suggests a rewarding relationship will develop.

The last scene in the premiere, in which she offers Lou a ride in her black cadillac, and then reconsiders, is a hoot. Throughout the program, writer Tokatyan leads characters to the brinks of cliches and then turns then away at the last minute to something inventive and credible.

A few lapses don't hurt the overall good impression. The creators of the show obviously didn't want to spend a lot of time on exposition about Grant breaking into his new job; they wanted to tell a free-standing story, so once Grant is hired, he jumps right into the job with no ado. It's abrupt, but probably a wise course.

Great care has been taken to portray newspaper life realistically - certainly more so than in such unlamented howlers as last year's "Andros Targets" on the same network. It isn't documentary-dull, but "Grant" does give reporters a break, which is not to say an unqualified kiss on the face.

It's even up-to-date; one of the first things Grant spots at the newspaper office is a video display terminal, one of those computer-linked keyboards and TV screens that have become common, if not universally, beloved, at many big-city dailies.

"Grant" doesn't glamorize the business of journalism, as "Andros," in its misguided way, tired to do. But for media folk it should be a special pleasure to watch - not infallibly accurate, but keen to real problems and to the varieties of human animal, drawn to journalism.

The premiere involves the conflict between a Watergate-high young turk reporter (Robert Walden) and a 30-year veteran police-beat man (Peter Hobbs) who has covered cops so long that he has practically become one. The story is resolved in arresting shades of gray; it concedes fallibilies in all the participants, including Grant.

But it also believes in an eventual justice that outs when decent people behave according to a code of decency.

"Lou Grant" is not so much upbeat or downbeat as sensationally sane. Unlike most of the new shows, it doesn't see the viewer as someone to be coddled, bamboozled or coyly titillated. There's a small scene near the middle that epitomizes the style; Grant is faced with a tough decision, so he sits down on a park bench and silently thinks it over while midday church bells chime.It's not a flashy or witty moment; it just strikes you as wonderfully, quietly plausible.

For Asner, "Grant" represents an especially trenchant truimph. Grant isn't just the kind of editor a writer would like to have; he's the hard-knock old pro anyone who relishes people would like to know.

Chewing his pencil at a news conference, regarding a prematurely double-take, testing out approaches to impress the loftly publisher, Asner proves Grant completely worthy of center stage.

"You're not afraid of me, are you?" he growls at a young reporter.

"No."

"Awwwww," Grant says. "That's too bad."

The supporting east includes Mason Adams as managing editor Charlie Hume, Adams is recognizable if you close your eyes and listen to him talk; his has been the unseen voice in dozens of TV commercials. He'll be proud he showed his face on "Lou Grant," though. it is a gruff and lovely credit to all involved. And to television.