YES, VIRGINIA, there was a golden age of television; don't you believe anything??? Actually, it is something people ought to be reminded of every now and then, if only so they'll be able to jeer and hoot authoritatively when some addlepated TV pooh-bah tries to say -- as Fred Silverman did a few years ago, before he ran out of networks -- that the golden age is "now."

Not now. It was in the '50s, when instead of a prime time jammed with sitcoms and soapcoms and soupc,ons of sex, TV offered several hours each week of live drama, often original work by bright young writers. One of them who remembers it all fondly is Tad Mosel, now 59 and a drama teacher at New York University, and then a busy member of a fraternity that included Paddy Chayefsky, Reginald Rose and Rod Serling.

"You will never hear me say it wasn't a golden era; I hate it when people say that," says Mosel from New York. "It was as golden as golden can be -- not a zenith, but a flowering period. If it wasn't flowering, I don't know what it was doing. It offered tremendous opportunity to young talent."

What Mosel learned writing for live TV he put to use on his first stage play, "All the Way Home," which won him the Pulitzer Prize for drama in 1961. Tomorrow night at 9 on Channel 4, NBC will air, live from a stage at UCLA, a new production of the play (which was based on James Agee's novel "A Death in the Family") starring Sally Field, William Hurt and Ned Beatty. That exceptional cast also includes Ellen Corby, sufficiently recovered from the stroke she suffered while playing Grandma Walton to take the part of a 103-year-old great-great-grandmother. "Home" will be directed by Delbert Mann, who directed the original live TV version of Paddy Chayefsky's classic, "Marty."

Mosel, who in his NBC photo looks as much like a credit dentist as a playwright, takes pains to point out that this telecast is not like the live dramas of the golden age. It will be performed on a stage in front of an audience; TV plays of the '50s were done in TV studios. The idea, he says (and keeps repeating) is to use television to recreate a theatrical experience; that's the plan of producer David W. Rintels.

Although he'll be at home in New York watching the play on TV like everybody else, Mosel says that as the airtime for "All the Way Home" approaches, he canSee AIR, D7, Col. 1 AIR, From D1 feel some of the exquisite and invigorating terror he used to feel when sweating out those last moments before air during TV's well-spent youth.

"Sitting in the control room while they counted down the last seconds was a thrill unequaled in any other medium," Mosel recalls. "It's something like a curtain going up in a theater, but there you're playing to 1,000 people or so. With TV it was 20, 30 million. It was so exciting, it was almost unbearable."

The playwrights who worked on TV then really were a creative community. "We all knew one another and we all cared about each other. We all wanted each other's plays to be wonderful. There was none of that modern stuff about 'It's not enough that I succeed, my friends must also fail.' " They were so close, he says, that "we never minded taking credit for each other's plays. People were always praising me for things Horton Foote had done. I took compliments for his plays all the time."

In fact, they all wrote so much, and so fast, that they sometimes forgot who had done what; Mosel has trouble recalling titles even now. How did they manage to be so prolific? "Well, we had unlimited gall," says Mosel, who once wrote a half-hour play in one night.

"Actually that was a rewrite of someone else's play. We would rewrite right up to the last minute. I'd be home on Sunday night watching 'The Philco Playhouse' and they'd announce my play for the following week. If they had time to fill, they'd even play a little scene from it. And I'd say, 'Well, good luck to you, because I haven't finished the third act yet.' "

Where did tha playwrights of the golden age go when TV double-crossed them, and the audience, and sold out to the filmed series? Some went into movies, some died, and some, like Mosel, wrote for the stage. "We moved on," says Mosel. "Those of us who learned our craft in television proved to be pretty much undaunted by anything else, because live TV was so hazardous."

He witnessed one or two of the fabled live goofs that were among the hazards. In a TV play directed by Mann in 1953, Mosel saw a woman getting ready for bed and a prop man accidentally stroll right into the scene. "He did the worst possible thing; when he realized he was on-camera, he clapped his hands over his mouth. Then he walked off.

"But I think audiences liked to see the actors pull themselves through; it was part of the collaborative nature of the experience. Unfortunately, they'd sometimes forget their lines, and now and then they'd leave out the entire point of the play."

Public TV is paying inadequate but often rewarding homage to the great days of TV with its series of archival retrievals, "The Golden Age of Television," produced by Sonny Fox. The "new" packaging for the old plays isn't very attractive or thoughtful -- in fact, it's junky -- but the series gives people under 30 a chance to see what all the fuss was about -- "Marty," "Days of Wine and Roses" and "No Time for Sergeants," among others. It's gratifying to learn that many of those plays were indeed just what they've since been cracked up to be; sometimes they even prove to be more than they were cracked up to be.

"Stars never appeared in our plays," Mosel recalls. "Always young industrious actors instead, people like Paul Newman, George C. Scott and Jack Lemmon. When they became famous later, viewers thought they'd discovered them and made them stars, and they had. There was a warmth of communication then that simply does not exist any more."