The boys are back in court. The girls too. But it's not the way we are used to seeing them -- all the senior partners at McKenzie Brackman sitting as crabby-faced defendants on tonight's overdue but triumphantly enjoyable season premiere of NBC's "L.A. Law," at 10 on Channel 4.

Not only are their butts hauled into court, but they have to suffer the indignity of hearing themselves referred to as "this stumbling, bumbling group of lawyers," "this collection of kooks" and "this unscrupulous bunch of thieving sharks."

That they are, and how we love them!

They're in court because naughty Rosalind Shays (Diana Muldaur), the corporate headhunter who did her job a little too well last year, wants a few more heads for her belt. She sues McKenzie Brackman for $500,000 over the way she was treated, charging the firm with sex discrimination on the basis of a comment made to her by Ann Kelsey (Jill Eikenberry) in the ladies' room nearly six months ago.

You don't remember that comment? Some "L.A. Law" fan you are! But it's replayed during an assortment of highlights in the pre-credits tease. Instead of "Previously on 'L.A. Law,' " they say, "Last season on 'L.A. Law.' "

And what a season it was; "L.A. Law" just took home its third Emmy as best drama series on TV. For the sake of convenience, Shays's lawyer also recaps many of last season's plot turns as part of the shellacking he gives the firm at the trial.

What else is on the docket this season? Executive producer David E. Kelley, who wrote the season premiere, said yesterday from Los Angeles that a case involving flag burning will come up, but the issue at stake will not be flag burning itself.

In another socially serious case -- one that gets underway tonight -- Michael Kuzak (Harry Hamlin) must defend a white cop charged with recklessly shooting a black teenager during an arrest. The incident attracts the attention of Paul Winfield as a grandstanding activist who would appear to be patterned on the Rev. Al Sharpton.

Kuzak bluntly enlists associate Jonathan Rollins (Blair Underwood) to be "window dressing" in court because Rollins is black, and public opinion against the cop is mounting.

"L.A. Law" doesn't shrink from tackling the really tough cases.

It's true that this is the last season for misty-eyed Susan Dey as Grace Van Owen, Kelley says; Dey did not want her contract renewed and has announced plans to leave at season's end. But as a result, Dey will be especially prominent in the weeks ahead. After a brief and wrenching stint as a judge, Van Owen joined the firm as an attorney.

It hasn't been decided how Dey's departure will be written into the script, but Kelley suggested he would be reluctant to let anything terrible happen to Van Owen. Nine of this season's 22 episodes have been written so far.

Although the Shays trial will end next week, Kelley said, it will "resonate" beyond that, and Rozaholics will be happy to hear she won't be crawling into the woodwork. "She's not a person who goes away easily," Kelley promises.

Two new lawyers will join the firm -- C.J. Lamb, played by Amanda Donohoe, as of the fourth show, and Tommy Mullaney, played by John Spencer (Harrison Ford's loyal ally in "Presumed Innocent"), in Episode 6. Kelley says that even without Shays in the firm, there will be plenty of bitter office politicking.

In the aggravated pathos department, yes, Vincent Gardenia is back as Murray, Roxanne Melman's (Susan Ruttan) delusionary daddy. He no longer seems to think he is Ralph Kramden, but tonight he learns he has Alzheimer's disease, and this will be a continuing plot thread. In a future show, Murray will move in with Benny (Larry Drake) and they will become ostensibly lovable if accident-prone roommates.

Now about this Arnie Becker marriage. Will it last? "We're betting on it here in the office," Kelley says. "I think he's a changed man. But it won't be an easy marriage, clearly." Tonight the formerly philandering Arnie (Corbin Bernsen) poses with wife and stepchild for an icky family Christmas card.

Another crisis in the McKenzie Brackman family occurring tonight should not be revealed in advance, except to say that the pressure of the Shays lawsuit takes its toll on one member of the firm in a particularly dramatic way.

One very brief and very odd scene tonight -- a scene that just hangs in the air and doesn't relate to anything else on the show -- has Abby Perkins (Michele Greene) picking up her son Eric, 9, and taking him to a baseball game. Kelley says the "freestanding" scene is there to help establish Abby as a mother so that she can get involved in parenting issues this season.

Kelley concedes that keeping a show both surprising and satisfying in its fifth season won't be easy. "It's tough to be fresh and new anyway," he says. "Our viewers are tough too. They're looking for twists and changes, and we're challenged to look for story lines that will help us stay ahead of them."

Television that challenges the people who make it and the people who watch it is the very best kind. With most of the new fall shows now revealed to be deadbeats or bummers, with some returning shows looking tattered after three or four weeks on the air, and with even "Twin Peaks" deteriorating into silliness, it's good to see "L.A. Law" back in such great shape.

Truly devoted devotees will note that in the "bumper" slides that precede and follow commercial breaks, the sticker on the "L.A. Law" license plate has been renewed through September 1991. Whoever issues those stickers knows what they are doing.