If you ever see Barbara Walters coming up your driveway with a film crew, you will know you've got it made. Walters and her primetime specials celebrate famousness; the topic is always success. Those whose homes she invades know they have achieved it or she wouldn't be there.

The 50th Barbara Walters Special (Tuesday at 8 p.m., Ch. 4) is a collection of highlights from the first 49. It celebrates Walters' success, too. She's become a bigger star than many of those she's interviewed.Why doesn't someone go to her house and snoop at her? She probably wouldn't allow it - or thinks she's the only one qualified and glamorous enough to do the interview. She's very wealthy, you know; she probably has a big iron gate and a flock of German shepherds.

On the special, she talks not only about her victories in interviewing the famous, but also about little embarrassments. She seems sorry that she said to President-elect Jimmy Carter, "Be wise to us, Governor; be good to us." Of course she's sorry. Who wouldn't be?

She is more concerned with being ridiculed for having asked Katharine Hepburn what kind of tree she would like to be. "She brings up the subject of a tree," Walters says defensively. Then she replays the tape to prove her point. Sure enough, Hepburn brought up a tree. Walters asked, "What kind of a tree are you, if you think you're a tree?" Hepburn said an oak.

Walters explains that when she started the specials in 1976, the idea was to mix showbiz stars with political figures. Jack Paar used to do this with aplomb on "The Tonight Show." But Walters says that even though she found her own interview with the Shah of Iran to be "riveting," the ratings were not pretty. And they "plunged" when she visited Vice President and Mrs. Walter Mondale.

So now, she says, she saves the politicos for "2020," the ABC News magazine show, and sticks to the glitzerati for the prime-time specials, which are made by her own production company. This gal is rich.

She does ask pretty good questions.

To Don Johnson: "When did you lose your virginity?"

To Richard Pryor: "Are you totally off drugs?"

To Boy George: "Are you bisexual?"

To Brooke Shields: "Who is Brooke Shields?"

No, not all the questions are good, but many of the answers are. She asked James Garner if he would do a nude scene. He said, "God no. I don't do horror films." Bette Davis gives the recipe for a good marriage: "Communication, separate bedrooms and separate baths."

The people who come off the best are those who seem the least impressed with themselves. Walters is staggered by Bing Crosby's modesty. In the last interview he gave, he tells Walters he considers himself a "terrible actor" and not a great singer.

Asked how he would describe himself, Crosby says, "Oh, I'd say he sang a fair song - in tune most of the time - that he could read lines pretty good, had a good sense of comedy timing, fair vocabulary. And not a bad fellow all around. That's it."

Laurence Olivier says, "I just don't like me." And Clint Eastwood says, "I don't have a lot of brains, but I have a good gut feeling." Tears come to the eyes of Patrick Swayze when he notes that his father did not live to see him achieve success.

There's more than talk. Walters goes jeep-riding with Ronald Reagan, boat-riding with Fidel Castro, elephant-riding with Jimmy Stewart, and yatch-riding with John Wayne. She sings with Dolly Parton, plays drums with Ringo Starr (about as well as he does, actually), clowns with Steve Martin and soft-shoes with George Burns.

Walters has grown thicker-skinned over the years so that she doesn't fly into rages when criticized any more. Perhaps she learned the secret of happiness from Bette Midler, who says the trick is to just stop caring what your detractors say.

Walters should probably feel guilty for paving the way for such imitators as the dismally voyeuristic Robin Leach. She made celebrity interviews big business - and now that business is too big. But it's worth remembering that her celebrity journalism was considered trashy when it started and now, considering what we have today, it seems a class act.

There has to be a best of everything - even of things not necessarily worth doing - and in her field, Barbara Walters is tops. She's America's gab queen and her 50th special is delightful. The 51st probably will be, too.