"NICHOLAS Nickleby" and "The Skin of Our Teeth" both provied that good theater can be good television -- indeed, that great theater can be great television. Neither of these plays was a smash hit in the ratings when recently televised.That doesn't matter a bit. That matters so little it is hardly worth discussing.

The people who did watch and did enjoy these plays -- "Nickleby" on the ad hoc Mobil Showcase Network of stations, "Skin of Our Teeth" on PBS -- probably got incalculable amounts of pleasure and satisfaction from them, the kind of reward you don't get from many television programs because most television programs aren't designed to be good, much less great.

But what both productions proved is that theatrical devices can work on the air, even though by the laws of vidio they probably shouldn't. In "Skin of Our Teeth," actors step out of character to say, among other things, that they can't stand the play, and at one point there is a mass defection by many in the cast. In "Nicholas Nickleby," the theatrical integrity of the original Royal Shakespeare Company production was preserved. We saw actors playing not only many different characters, but pieces of scenery, props, a carriage; and we saw them performing sound and stage effects.

Actors spoke narration directly to the camera, yet somehow this didn't compromise the credibility of the Charles Dickens story at all, and only increased its charm. Perhaps there are a number of technical explanations for the success of this transition from stage to tape, from the Old Vic to the living room, but the simplest one is also entirely acceptable: "Nicholas Nickleby" was magic, and magic doesn't need to be explained.

"The Skin of Our Teeth" was magical, too; this play always has been, since Thornton Wilder wrote it in 1942 and it won the Pulitzer Prize. "Skin of Our Teeth" was the 1983 premiers telecast for the praiseworthy and frequently superb "American Playhouse," which in its 39-week season will present 20 new productions (some multiparters) and 17 repeats. Because some of the "Playhouse" shows are on film, not tape, they don't quite qualify as theater, but that's splitting hairs.

"American Playhouse" is a boon and a blessing and not to be quibbled about.

Surprisingly, though, this "Skin of Our Teeth" was, according to PBS, "the first live telecast of a theatrical stage production in the history of public television." For shame! In 25 years they never did another live paly? "Skin of Our Teeth" arrived not a moment too soon. It proved to be several moments too long, however, spilling over 20 minutes past its appointed hour of conclusion, but more power to "Playhouse" for not cutting the original text.

In production notes, PBS emphasizes the crisis orientation of Wilder's work; it was first written in wartime, then revived during the Cold War, and now here it was again, to remind the human race, in an era of frightening economic uncertainty, that it has always had a way of surviving calamities, even those it brought on entirely of its own incurable stupidity (in this sense, it was appropriate that Wilder's play about renewal was broadcast live from the Old Globe Theatre in San Diego, rebuilt and reopened after having been destroyed by an arsonist).

Wilder wrote in his own introductory notes to the play that its two lead characters, Mr. and Mrs. Antrobus, "have survived fire, flood, pestilence, the seven-year locusts, the ice age, the black pox and the double feature, a dozen wars and as many depressions... They have survived a thousand calamities by the skin of their teeth. Here is a tribute to their indestructibility."

The PBS production proved a tribute to a play's indestructibility. Largely this was due to three key performances: Harold Gould's every-mannish Mr. Antrobus, Blair Brown's wittily frivolous Sabina, and, most of all, Sada Thompson, who was as magnificent as the Rockies in her portrayal of Mrs. Antrobus, hale and imposing and stalwart to the hilt. And even beyond the hilt. Great plays are not just processions of great moments, but Thompson had her greatest moment near the end of the second act, when she made Mrs. Antrobus' speech about the mysteries of womanhood sound like the most eloquent and timeless feminist statement ever made.

Mrs. Antrobus has just thrown something into the ocean off Atlantic City. She says, "It's bottle. And in the bottle's a letter. And in the letter is written all the things that a woman knows. It's never been told to any man and it's never been told to any woman, and if it finds its destination, a new time will come. We're not what books and plays say we are. We're not what advertisements say we are. We're not in the movies and we're not on the radio.

"We're not what you're all told and what you think we are: We're ourselves. And if any man can find one of us he'll learn why the whole universe was set in motion. And if any man harm any of us, his soul -- the only soul he's got -- had better be at the bottom of that ocean. And that's the only way to put it."

The frustrating thing when confronted with a performance like this on television is that there's no way, sitting in one's home, to tell the actress how much she's appreciated, how stunningly she's hit the bull's-eye, although the audience in the Old Globe did burst into applause when the speech ended. The ABC series "Family" got awfully trite and tired in its "sensitive" sermons about family life, but Sada Thompson, and her costar, the late James Broderick, were the constants that gave it feeling week after week.

Sada Thompson is an extraordinary and gifted actress, and yet television gives such performers few chances to prove themselves. The major challenge they face is maintaining a sense of self-worth while putting themselves in the service of mediocrity.A live dramatic role is the true test of acting prowess; movies and taped TV shows can all be faked, more or less. That's one value of live performances on TV. Another is the momentum that is built up by actors who perform a play from its beginning to its end; they get caught up in it, they are transformed by it; and the people watching know it will never happen just exactly this way again.

Anyone who says there's no difference between a live TV show and a taped TV show is just plain crazy. Being live is no guarantee of being exceptional, of course. An "NBC Live Theater" production of "A Member of the Wedding" earlier this year, despite the impassioned efforts of young actress Dana Hill, tended to just roll around the room, thudding against the walls. The play creaked, and many of the performances seemed listless. It wasn't good television or good theater.

For the record, PBS' was not the first television production of "The Skin of Our Teeth." It was staged live on NBC on Sept. 11, 1955 -- a "Sunday Spectacular" starring the famous director George Abbott as Mr. Antrobus, Helen Hayes as Mrs. Antrobus, and Mary Martin as Sabina (a role created by Tallulah Bankhead). The late Alan Scheider directed, and John Cameron Swayze appeared "as himself," because the role of a newscaster was merrily written into the proceedings by Wilder. On the PBS version, which included some harmless updating that changed radio references to television references, the newscaster's role was wearily and poorly played by the criminally overexposed John Houseman.

Early ratings indicate small audiences for "The Skin of Our Teeth." In New York, Los Angeles and San Francisco, there was an enormous drop-off in viewing from the program that preceded the play, a "Nova" installment called "Hawaii: Crucible of Life." But television has spent years educating the American viewer away from live drama; no one can justifiably expect the nation to thunderingly rally forth just because an effort is made to revive it.

Others will try, some will succeed. There's an almost uncountable number of plays, American plays, that are worthy of revival on television, either restaged as studio productions or performed as theatrical events, the way "Skin of our Teeth" was. Pay-TV operations like Home Box Office offer taped plays, but what plays -- Neil Simon and "Camelot" and that sort of yech. There's so much more there, waiting to be rediscovered, and there's an audience out there that hardly gets anything meaty and nutritious to chew on.