In the eight years I've been reviewing television shows, the vast majority of them have been made available to critics before they debuted.

And in every single instance when they were not, the shows have turned out to be bad. Or worse.

Keep that in mind when I tell you that CBS did not let critics get a look at "Four Corners," its new prime-time soap opera that opens with a two-hour movie tonight at 8 on Ch. 2.

We're told that the lack of review cassettes is "due to the late production start . . . and subsequent weather-related delays." And that sounds logical and un-der-standable.

But it also sounds like the excuses every network has used every time it has withheld pilots from critics. And, once again, all those shows were bad.

There's also the somewhat suspicious fact that, of all of CBS's midseason series, this was the only one that was not the subject of any network sessions during the TV critics press tour in Pasadena last month. And there were other shows - including "The Closer" - that did not have completed pilots to show the critics at the time.

Here's what we know about "Four Corners" without having seen the pilot:

- It's an hourlong drama from the creator of "Dallas" and "Knots Landing."

- It's Ann-Margret's first weekly television series.

- She plays Amanda Wyatt, the widowed matriarch of a Southwest ranching family. Her best friend, Carlotta (Sonia Braga), was also widowed by the same plane crash that killed Amanda's husband.

- The basis of the drama is upper-class vs. lower-class, Anglo vs. Hispanic. And both women have over-heated twentysomething offspring causing all sorts of troubles - including Amanda's daughter, who is hot and heavy with Car-lotta's son.

What we also know is that "Four Corners" has had script problems ever since it was proposed to CBS a year ago. That it failed to make the cut for the fall 1997 schedule. That it has undergone some serious revamping since then.

And, of course, that there's no pilot for critics to review.

Maybe "Four Corners" will be the exception to the rule. Maybe it will be a great show.

Just stay tuned . . . and don't hold your breath.