A brisk, thoughtful shocker that manages the trick of surmounting its own implausibilities, "News at Eleven" takes aim at a target that television usually ignores -- television itself. The CBS movie, at 9 tonight on Channel 9, is a beneficial exercise in exploiting the exploiters. It views local TV news with a very contagious alarm.

Essentially, it's "The China Syndrome" of eyewitness newscasting.

Martin Sheen, who always seems to turn up in conscience-stricken TV movies like this, plays a San Diego anchorman drawn into complicity on a tawdry sex story that proves just the bitter tonic for boosting his station's news ratings. The villain of the piece is the station's new hotshot news director, a liar and a zealot who listens in on his reporters' phone conversations and thinks the idea of ethics in journalism is plainly quaint.

Peter Riegert contributes a quintessential sense of smarm in the role, so that even when the plot becomes slightly preposterous, his nasty energy deflects one's incredulity. The story is also strong enough -- or maybe just audacious enough -- to carry a viewer through the inevitable windy speeches about morality and TV newscasting and whether the two are mutually exclusive.

Anchor Frank Kenley (Sheen) has returned to the San Diego market after failing in the big time, New York, perhaps because he has just Too Much Integrity. Scarcely has he been ballyhooed as San Diego's answer to Dan Rather when a sleazy story surfaces about a local junior high school teacher accused by a 14-year-old student of having seduced her.

The news director wants to run with the story, and when he does, the ratings for the previously low-rated newscast start to bubble. Kenley's misgivings grow when writer-director Mike Robe's script conspires to involve him personally in the accused teacher's story. A friend of the anchor's teen-age daughter admits in an ambush interview that she, too, had sexual relations with the teacher, who up to that time had looked like the innocent victim of an emotionally disturbed adolescent.

Robe confuses his own case when he shifts gears on the teacher, but if he hadn't, the film would have become the teacher's story rather than the anchor's. Unfortunately, some of the plot turns become grievously far-fetched, as when the news director insists on airing the ambush interview even after charges against the teacher have officially been dropped.

In a nation, and an industry, that has enough lawyers to do "Hands Across America" every day of the week for a year or two, it seems glaringly odd that this San Diego TV station never even considers running these highly litigable stories past house counsel.

Even so, the subject is so ripe that the details seem not to matter. The news director hides behind hollow cant; he brandishes the First Amendment like somebody's advertising slogan. "The public has a right to know, and it's our obligation to report," he says defensively. His real passion is reserved for a later speech to his staff after breaking the sex scandal story: "You know, our ratings jumped half a point on this last night."

During an interlude at the corner bar, anchor Kenley and a veteran coworker talk about television news. "Every sweeps month we go through this," the coworker says of the sensationalistic stuff. "We hype the ratings four times a year and we charge our advertisers accordingly."

Perhaps as a sop to its own affiliates, who might be viewing this movie with a certain testiness, the CBS film even implicates the networks, in a way. " '20/20' does an in-depth report on Cher's Broadway opening," the old veteran grumbles, "and '60 Minutes' does Johnny Carson . . . 'Riptide,' Rather, it all comes from the same box. Monty Hall was once an anchorman. Mike Wallace was a game show host."

This may not be the most sophisticated media criticism in the world, but for it to be uttered on prime time is something of a breakthrough. And unlike such previous television films as "Pray TV," a namby-pamby huff at the evangelical broadcasting industry, "News at Eleven" really does seem to have a tough, aggressive attitude.

Barbara Babcock plays a deputy district attorney who's a very forgiving friend of Kenley's. Sydney Penny, who made such a memorably cute debut in "The Thorn Birds," does a fine job as the anchor's 15-year-old daughter, who is appalled by the insensitivity of the reporters ("I think TV news stinks" is the way she puts it). Sheree J. Wilson is particularly pungent as Christine Arnold, a young and pretty anchor at the station who is not hampered by Kenley's inhibiting sense of responsibility.

Real TV news directors and reporters may find much to scoff at in the scenario Robe has conjured for this picture, but the basic troubling points it makes are valid and, considering the forum, refreshing. Robe is also skillful enough as a dramatist to have invented a satisfying comeuppance for the ruthless news director, whose utter ignorance of the community he claims to be serving eventually helps do him in.

In a telephone conversation with the station owner, the news director agrees that "the news has to pay for itself from now on." Indeed, for local stations, the news is a major profit center. There are aspects of "News at Eleven" that recall real-life excesses of TV stations bounding heedlessly after a buck and trampling rights of privacy, or other rights, or simply good manners, in the process.

Yes, "the media" as whipping boy is getting to be a cliche'. But as even some paranoids are actually being chased and hounded, some whipping boys now and then truly deserve a thrashing. "News at Eleven" gets in a few good licks.