"Kaz" is the "Rocky" of lawyers - a hard luck underdog determined to hang in there. Hey, I kinda like this bum.

The new CBS series about a two-fisted attorney who earned his law degree during six years up the river - and who may be restricted to the use of one fist with the crackdown on TV violence - gets a "special preview" Sunday night at 10 on Channel 9. From the look of the first episode, the program is one whose stories may ring patently false but whose roughhewn title character is a hearty addition to TV's heros.

Ron Leibman, who plays the part, makes the character's flaws and vulnerabilities as important as his big personality asset - the desire to improve his lot in life (one of the great themes of series television) and to help keep fellow outcasts from spending great chunks of their lives in jail.

It is never suggested that hero Martin Kazinski was wrongly jailed or framed; merely that he was partly a victim of environmental circumstances. The character as played by Leibaman has winning and stubborn resilience. The best scenes in the first show are the early ones in which he reenters society armed with inky-wet business cards that smudge people's hands and a frame diploma that falls off the wall and crashes to the floor of his crummy apartment.

He moves smoothly through the world of street crime, knowing it first-hand, but neither the show or the character exhibit the cry-baby demagoguery that made "Baretta" so unbearable. "Kaz" is hardly free of simplistics, but it's far better than the average crime show.

The real beauty of Leibman's performance is its dimension, the little glints of desperation he lets filter through the swaggering facade. This sustains Leibman even when the script, by Sam H. Rolfe, has Kaz doing overly cute-brash things, like visiting establishment lawyer Sam Bennett (the perfectly cast Patrick O'Neal) at his home on a rainy night.

"This," says O'Neal, "is beyond belief," and so it Kaz's eleventh-hour courtroom victory on his first case. But Leibman's slap-on-the-back smile and give-me-a-break bravado make "Kaz" very close to irresistible.

In "The Paper Chase," a new CBS drama series that gets its first airing tonight at 8 on Channel 9, we have the most prematurely overpraised TV programs of the year. It's been hailed in advance as literate and intelligent - perhaps because it takes place at a college.

But in a TV season already overcrowded with lawyers, "Paper Chase" hardly seems a novelty of heroic proportions, and the fact is, problems of a young law student in dealing with the Moby Dick of professors do not hold much dramatic potential for series television. The first episode, in which the student is sentenced to classroom anonymity after he flubs in class, is handsomely produced and well-written, but it hardly leaves one breathless for further adventures on the campus.

The film on which it is based - a curiously inconsequential and inconclusive drama - was overpraised too, but in both the film and the TV version, John Houseman, now 75, is indeed an imposing presence as Kingsfield, professor in excelisis. The problem is, Houseman could do the role in his sleep by this time, and might as well, and the relationship between him and student James Hart (James Stephens) doesn't have many promising possibilities.

The premiere was written by James Bridges and directed by Joseph Hardy. A futuje chapter will be scripted by John J. Osborn, Jr., author of the original novel. This is all very prestigious, but the fact is, "Chase" plays noble but dull.

"You don't know how rotten the top can look until you've seen it from the bottom," snarles Jack Cole, whose father has been swindled and murdered, whose mother has dropped dead of heart failure, and who himself has been railroaded into three years of prison. And that's just in the first 15 minutes of "Sword of Justice," 2-hour premiere of a new 1-hour NBC adventure series airing Sunday at 8 p.m. on Channel 4.

Cole, played by Dack Rambo, sets out not only to avenge moms and pops, but secretly to fight that "whole level of crime" that goes on "way above the law," and it sounds as if he's going to be a kind of Superman of Watergates. But - no.

Instead, the program degenerates tediously into a cross between "Switch" and "It Takes A Thief," with a little "Batman" and some "Mission: Impossible" thrown in. It seems Jack is going to catch crooks by setting up elaborate con jobs and sneaking through their file drawers. One begins to long for an outburst of gratuitous violence as the charade piddles on.

Rambo is certainly sufficient when playing the cream puff by day, but as the derring-doer by night he is unconvincing. Bert Rosario has been handed the insulting role of Cole's Puerto Rican accomplice (they were cell-mates in the clinker) and performs approximately the function that Willie Best and Mantan Moreland served in movies of the '40s. Except he never says, "Los feets, don't fail me now."

One might have feared that when NBC's news magazine "Weekend" moved from late night to prime time, the little shop on the corner would overnight be outfitted with computerized checkout counters. This has not happened. "Weekend" makes the passage, as of Sunday night at 10 on Channel 4, with its caustic integrity, sting-ray vision and big soft heart intact.

It is still a marvel of the air.

Shortened to an hour and attractively jazzed up with new music bridges and animated titles, "Weekend" maintains its begruding sardonic respect for human folly; the show's set is still a movie theater marque and the picture that's always playing is a silly weepy melodramatic tragicomedy called LIFE. Producer Reuven Frank and director Gerald Polikoff have tightened the pace - perhaps too zealously for comfort at times - but the tone and attitude are as they were, and they neither duplicate nor imitate anything else on television.

Loyd Dobyns' opening report on England's test-tube baby was not available for advance screening, but the rest of the show was. It includes producer Vernon Hixon's beautifully edited report on Sheldon Levy's Action Movie News operation in New York, which specializes in capturing misery and mayhem in the city's streets on tape and film for the city's TV stations; and producer Craig Leake's gentle heartbreaker on the Southwestern Book Company and the students who sign up each summer to sell its books door-to-door and thereby grab a slice of American pie.

This eassy on the success ethic keeps one teetering on the laughter and tears fulcrum more deftly than almost any piece of fiction recently on television. The beauty of "Weekend" is that one does not feel shoved or manipulated; it's a news show that has the humility to let we poor viewers read something into it ourselves.

Of course, it isn't above coaxing as a little.

Lloyd Dobyns is abetted in his hosting chores this season by reporter Linda Ellerbee. No one can top Dobyns at scoring effortless acerble bull's-eyes, and Ellerbee doesn't try. She does have two problems. She has trouble modulating funny kickers, so that her punch lines don't always register. Also, she looks like an entirely different person in reports on film than she does on tape in the studio. Something about her hair.

One good thing about male reporters on TV is that most of them don't mind always looking exactly the same.

One new feature of prime-time "Weekend" can go right now; the "columns" - one on sports and one on food - that interrupt the show and swim against its visual current. Otherwise it's all perfect, in a roughhouse sort of way. Tempted as we are to make comparisons with ABC's herky-jerky "20/20," "Weekend" beats us even to that pleasure; there's a final, last-minute zinger that will end Americas Sunday with a hugh roar of nasty laughter.