HBO's "Oz" returns for a third season of eight episodes tonight with its nasty power undiminished. Rare is the installment of this very visceral prison series that doesn't contain a moment so horrific it threatens to take your breath away.

Usually that involves sudden, shocking violence, rather a natural hazard in a building full of murderers, rapists and armed robbers. Death is ghastly enough by itself, but on "Oz," producer Tom Fontana and his collaborators keep finding ways to make it even ghastlier.

Clearly not everybody's cup of red-hot lava, "Oz"--returning at 10 p.m.--is the kind of show one can greatly admire for its sterling craftsmanship, striking style and kick-butt daring and still not exactly look forward to--or feel safe in recommending it to any but the most stouthearted of friends.

As the season opens, the Oswald Maximum Security Penitentiary has had its name changed to the Oswald State Correctional Facility. Our on-camera inmate-narrator (Harold Perrineau) explains that the change may reflect the fact that in this place, "nobody's penitent." The prison setting strips away most of the pretense and niceties of normal society and reveals men at their most repugnantly primal.

Women can be primal too, of course. Among that minority in Oz is Shirley Bellinger (Kathryn Erbe), a death row beauty who looks as if she wouldn't harm the proverbial fly--but did something much worse--and a new arrival, guard Claire Howell (Kristin Rohde), so preternaturally predatory that she makes some of the men look like pussycats.

One problem with the show is an embarrassment of riches where acting talent is concerned. Invaluable regulars like Rita Moreno, B.D. Wong and Edie Falco (who's sensational on HBO's "The Sopranos" as Tony's wife) seem to appear only for glimpses, and illustrious newcomer Milo O'Shea pops up only briefly as a new head of health services at the prison, part of the slimy governor's privatizing and cost-cutting campaign.

Among the most daunting new arrivals tonight is Snake, a surly con played by Treach, a rapper with Naughty by Nature. Convicted of armed robbery, Snake blabs braggingly to fellow prisoners of having committed a far more heinous crime. This plot line, planted tonight, is further developed in next week's episode, which was directed by actor Matt Dillon.

As an actor and talk show guest, Dillon often appears not to have a brain in his head, at least so's you'd notice, but he does a solid job of building suspense in the episode--as does director Nick Gomez, an old "Oz" hand, in tonight's opener. Other actors directing shows in the series include Chazz Palminteri (the episode airing Aug. 4) and the always-intriguing Steve Buscemi (the episode that airs Aug. 11).

No less prestigious an actor than Uta Hagen will appear in next week's show as the mother of an inmate. "Oz" attracts some of the best talent working in television, even though being a guest star on the show often means your character will end up sliced, diced or impaled.

Flashbacks and narration will help bring newcomers up to speed on the various factions and tensions that rule the Emerald City, as part of the facility is called. The loathsome Aryan brotherhood continues to be led in sundry conspiracies by super-sinister Vern Schillinger (JK Simmons) while the Muslims plot their own counter-offensive, led by, among others, Adewale Akinnuoye-Agbaje as Simon Adebisi.

Among the most touching continuing relationships is that of the O'Reily brothers, Ryan and Cyril (Dean Winters and Scott Winters). A somewhat weak link in the cast, Terry Kinney, still seems sappy and sanctimonious as Tim McManus, chief of the corrections officers. Ernie Hudson is strong as ever as the warden, however, and his son, Ernie Hudson Jr., arrives tonight as a young inmate whose significance in the story will grow in future episodes.

So there you are--by the time an exhausted critic has listed just part of the admirable cast, revealed a plot line or two and meted out the requisite praise, it already seems he's gone on and on.

Suffice it to say that "Oz" remains full of treachery, terror and sudden moments of quixotic tenderness. No one could be blamed for wanting to hide behind the couch until it's over, but those who do watch are likely to find themselves gripped, buzzed and spellbound.

CAPTION: Terry Kinney, left, and Edie Falco in HBO's "Oz."

CAPTION: Eamonn Walker in the uncompromisingly gritty prison drama "Oz."