LUCILLE BALL is soaked to the skin by a sprinkler on the CBS Lucy special airing Monday night. Later, she steps into a vat of Potato salad and then she sits on a cake. It's all in the line of suffering for one's art.

How many different substances has she been doused with during her 27-year television career? "OH-HO!" laughs Lucille Ball over the telephone from Los Angeles. "That's one I haven't counted. Well, there's water, milk, ink, dye, uh, the stuff they use in fire extinguishers, and, oh God, I've ridden in the Colorado rapids - besides water from a hose and almost drowning in a shower. I was in the tank at Marineland with the porpoises for an hour and half - I was really in there, too - and gee, what other stuff did we - oh, a lot of wet substances, a lot of mushy stuff like dough and mud and all kinds of gooey mixtures."

She is reminded of the time on one of her later shows when she sank up to her lower lip in what was supposed to be quicksand with Jack Benny. "Oh yeah, I forgot about that one. And that was real goo. Gritty goo. That was real gritty goo."

And, bub, that was entertainment . What Lucy did on television, especialy on "I love Lucy" during the '50s, was not very subtle and did not address social realities of its time or any other, but it was clowning in such a timeless vein that "I Love Lucy" reruns a quarter-century old are still drawing audiences on TV stations all over the world. She's the most enduring personality in the history of television.

On "The Lucille Ball Special," Lucy tries to recapture the madcap charm of those early shows and, even at 66, shows a flair for slapstick and comic timing. But the script is feeble and formula, the mishaps contrived, and the median age of the cast so high that the hour begins to look like the Miami Beach follies of 1977. The pathos is all unintentional; it would be better if the writers had put some in on purpose.

The program reunites Ball with Vivian Vance, the original Ethel Mertz, Gale Gordon, who appeared on her subsequent series, and Mary Jane Croft, who played the snobbish neighbor on later episodes of "I Love Lucy" (she was the "Phyllis" of the black-and-white age). It was directed by Marc Daniels, who directed the first episodes of "I Love Lucy," and written by two former "Lucy" writers, Madelyn Davis and Bob Carroll Jr.

"We had a ball," says Lucy. "It was a big, wonderful reunion. Vivian and I hadn't worked together in years, years. There's a lot of Lucy in action in the show, a lot of Lucy shtick. I have a different last name but it's still Lucy." Because she broke her leg four years ago while making the movie "Mame," she cannot bounce around the way she used to. "My leg is fine, but I can't jump up and down on it or do the physical things that I love to do," she says.

She attributes the success of "I Love Lucy" and the durability of the Lucy character to the fact that her shows were well-written, performed live in front of an audience, and never dealth with current events. There are no episodes with titles like "Lucy Gets an Abortion" or "Ricky Has a Vasectomy." It's too pat to declare today's situation comedies superior to the slapstick of the '50s on the grounds that they are far more relevant, because when you gain relevance you lose something else. Those old "Lucy" shows are possessed of a comic spirit - an organic rather than a contrived zaniness - that all of today's comedies lack.

So naturally, though Lucy says she enjoys watching "All in the Family," she did not approved of the recent episode - written by two of her own former writers - in which Edith was threatened with rape. "I didn't like that," she says. "I thought that was unnecessary. I wouldn't have done it. It was very well done but I don't think they needed it.

"I never did topical things. That's why we're still in reruns in 82 countries."

Not being topical is no more an automatic virtue than being topical is, most comedy series are dissapointments no matter what their degree of topicality. What the "Lucy" character has inits favor is that it was drawn in a classic clown tradition; "I Love Lucy" was basically performance comedy, while most of the best comedy on television today is script comedy.Lorne Michaels, producer of NBC's "Saturday Night Live," says he noticed the distinction when he was advising the network on comedy sequences for its first "First 50 Years" nostalgia special last year.

"A lot of Sid Caesar just wasn't funny any more," Michaels found when he looked at old kinescopes from the vault. "It depended to much on the script. Writing dates more than performance does. The stuff that held up was Milton Berle - basic comedy."

And the sad fact is that basic comedy is poorly represented on television today, except for reruns of old shows. The second "First 50 Years'" special on NBC, a forgettable compilation by and large, came ironically alive in its last five minutes, when Frank Sinatra sang "Send in the Clowns" over faded footage of great comics on early television - Bert Lahr, Ed Wynn, Fred Allen, Berle, Benny, Abbott and Costello, Groucho. It was devastating, it was heartbreaking; it said in effect, "This will never happen again."

In the '50s, the great clowns came to television from other spheres - film, the theater, radio - in search of the greatest audience of their lives. The audience and the clowns found each other and vaudeville was momentarily revived. BUt the demands of TV ate up a career's worth of material in a few year.

"It's a wild medium, television," says Lucy. "The closeness of it! It was apparent from the first two years we were on the air. At the time it was a great surprise because we had no idea that people would run up and want to touch you. What had to get used to it, because they had never done that before. But they felt so close to you because you had been in their living rooms. Now of course, it's old hat. Everybody knows it. Television is the quickest form of recognition in the world."

"I Love Lucy" wasn't only Lucy. The ensemble acting company was incomparably charismatic, especially Vance and the late William Frawley as neighbors and landlords Fred and Ethel Mertz. And of course, Deai Arnaz, then husband of Lucill Ball as well as "Lucy Ricardo" and the pioneer of the three-camera film technique still used on some comedies. Arnaz wrote his first book, "A Book," last year and Lucy, now married to Gary Morton, read it. She thought it was "very well done," too.

She has also read "Lucy and Ricky and Fred and Ethel, The I Love Lucy Book," now in paperback, and thinks it's probably "the best one done," although she says it overstates the backstage friction between Vance and Frawley.

"That wasn't quite true. He was the same in real life as he was on the screen; he was an irrascible gentleman and sort of crusty and he got a little loaded once in a while and shot his mouth off in front of the writers and they took advantage of it. But most of the one-liner were aimed at getting laughs rather than being a putdown, because when he and Vivian were together, they shared the same lawyer, they cried, they talked, they hugged and kissed."

On "The Lucille Ball Special" Lucy plays an Indiana housewife who gets through to President Carter on one of his phone-ins and invites him to dinner; he doesn't come but Miss Lillian makes a separately taped guest appearance at the end. It's pale comedy; the only things that matter on the show are the memories it stirs of the old days of Lucy and Ethel. At one point they spritz one another with spray cans full of red frosting.

When Vance enters Lucy's home with a "How ya doin' girl?", anybody brought up on "I Love Lucy" will get a deja vu little thrill. Lucy is by no means what she once was, but it's reassuring to see that one of our clowns is still clowning.