You can't avoid being intrigued when a TV star opens his first conversation with you by saying, "Do you want to hear the truth, or do you want to hear the press agents' bull excrement?" (using the ruder term for excrement, of course). That's exactly what David Hasselhoff did, drawing himself up to his 6-feet-4-inch height and staring down through startling green eyes under a mop of curly dark hair.

The star of Knight Rider then proceeded to give examples of truth versus press agentry. "The first thing they wrote," he growled, "was that I was discovered by Joyce Selznick, the movie talent executive, when she walked into a restaurant in Marina del Rey where I was working as a waiter. Actually, someone set up an appointment for me to see her in her office at Paramount Studios. I guess she forgot about me because I waited for her for nine hours. Then she arrived, looking very tough with a cigar in her mouth, and the first thing that happened was that her dog bit me on the leg. While I held a handkerchief to the wound, she said, 'Can you act?' I said 'Yes.' She said, 'Bull excrement. But you have the look, so I'll take you on as a client'!"

Another public-relations myth exploded by Hasselhoff is a statement in an NBC biography to the effect that he left the soap opera The Young and the Restless and the very next day was signed for Knight Rider causing him to exclaim, "I have to believe I have a guardian angel.

"More bull excrement," said Hasselhoff. "I had been in The Young and the Restless for six years and I was going through the worst period of my life: tired of playing the part of dashing Snapper Foster; tired of devoting all my waking hours to learning 25 pages of script every day; tired of being turned down for parts in prime-time series. I was drinking too much and blowing all the money I made. But I still was very much in the afternoon soap."

It was then - March 1982 - that Soap World, a show about soap-opera stars, invited Hasselhoff to grace its booth at a convention of TV syndicates in Las Vegas. "I was glad to get away for a weekend of gambling." Hasselhoff said, "so I did it. The ladies swarmed around the booth yelling,'Hello, Snapper.' A lot of them didn't even know my real name until I signed the autographs. They said,'David What?' "

Hasselhoff continued: "When the convention was over, I took a plane back to L.A. A man a few rows away kept looking at me. Finally I said to my seatmate, an entertainment lawyer,'Who is that guy who keeps staring at me?' The lawyer said, 'Don't you know? That's Brandon Tartikoff, the Entertainment president of NBC.' I said to myself,'Oh, boy.' I straightened my tie, fixed my hair and got up to go to talk to Tartikoff. But the minute I stood up, the seat belt sign went on and the stewardesses made me sit down in my own seat. We were flying through a storm, so the same thing happened three other times. When the plane landed at Burbank Airport, I ran after Tartikoff, but he got into a waiting limousine and took off before I could reach him.

"I said to myself, 'Oh, well, I've blown it again.' But the very next day, I got a call to come and test for the lead in NBC's Knight Rider pilot. I didn't find out until later that Tartikoff had turned to his seatmate on the plane, a guy who knew me from the afternoon game show Fantasy, and had asked, 'Who is that kid back there? I saw women leave the slot machines to waylay him at the convention, and here he is again on the plane.' The Fantasy guy told him my name, and that's how I got the call. But I still had to go through a lot of hell and uncertainty, plus more Young and the Restless, before I finally got the part."

So much for Hollywood legends. Hasselhoff delights in deflating them. "There's my costar in Knight Rider, for example," he says. "lt's a car- a souped-up computerized Pontiac Trans Am called Kitt, that can talk, think, fly 50 feet through the air, drive by itself, intercept police calls, elevate me through its roof, push huge dump trucks out of the way, plough through walls, do 10 times as much as the General Lee in The Dukes of Hazzard. But in one show, Kitt was faced with the simple task of towing the car of a young woman who had stalled along the highway. Kitt broke down trying to do the tow, and we had to improvise a line for the car to say to me. It's not generally known but the voice of the car is the fine Broadway actor William Daniels, who stars in the flesh as Dr. Mark Craig in St Elsewhere. When the car couldn't make the simple tow, Bill Daniels had to explain in a haughty tone of voice, 'Towing is not my thing'. "

With his chronic honesty, Hasselhoff says, "Who could believe that NBC could make it with a show about a guy who goes around solving crimes in a car that talks? It's kind of like 'Police Story Meets R2-D2': but here we are, holding our own against Dallas on Friday night. God knows, we're not beating Dallas, but we're getting a respectable share of the audience: sometimes as high as 28 percent (Knight Rider's average share for the entire 1982-'83 season was 25.) No other NBC show ever survived in that spot. In the TVQ ratings, which measure how much audiences like all the series on the air, we ranked No. 2 in December, just behind M*A*S*H. It's a miracle."

The TV critics think it's a miracle, too, since without exception they panned the series when it made its debut last September. Even the show's developer, executive producer Glen A. Larson, occasionally expresses wonderment. Larson considers himself an expert in what is wanted by what he calls "the middle of the country."

Larson says, "The middle of the country wouldn't go for another My Mother, the Car or another fender-bender like The Dukes of Hazzard.They've had enough of that. So we developed this modern Lone Ranger concept, with a guy rushing about righting wrongs, but riding in this crazy car instead of on his horse, Silver. But who would believe it unless we did it tongue-in-cheek, like Sean Connery did in the James Bond pictures or Christopher Reeve in 'Superman'? If we played it straight, it would be ridiculous. The problem was, 'Where are we going to find the right actor?' Then this kid David Hasselhoff walked in. He was totally irreverent. The first time the car talked to him. he burst out laughing. He kept adding little shtick of his own, like calling the car 'Buddy,' and patting it Iike it was a horse. He's the main reason the show works. He has that mischievous look in his eye that tells you, 'Of course you're not going to believe this, but lean back and enjoy it anyway'."

Larson adds: "Not that David's perfect. He still has those bad soap-opera habits, like dragging scenes out, and he's already gotten nto the star syndrome of demanding a bigger and more expensive mobile-home dressing room. He may have a point, though. He's so tall that he kept bumping his head on the low roofs of the cheaper models. So we finally got him the super-deluxe model."

It took a long time before Larson's and Hasselhoff's paths crossed. While Larson was a pop singer with the 1950s Four Preps group and later a writer-producer at Universal Studios, Hasselhoff, the son of a Brink's Inc. vice president, grew up in such places as Baltimore, Jacksonville and Atlanta. He began acting seriously at Lyons Township High School in La Grange, Ill., eschewing basketball despite his considerable height. He says, "I looked like a skinny giant stork in those days. I told them I couldn't play basketball, but they made me try out for the school team anyway. Then they said, 'You're right. You can't play basketball'."

Admittedly "spoiled rotten" by his parents (he was the only son among four daughters), he was allowed to float from one play to another in high school and in outside theater groups. "As a result," he says, "I ended up with such terrible grades that the hot-shot glory boy who played leads on the stage couldn't get into college. So I went to California Institute of the Arts (in Valencia) to study more acting."

Once he got to Los Angeles, Hasselhoff worked as a waiter and played what he refreshingly admits were one-line parts in TV series. He tells the ultimate neglectful agent story. He says, "I hadn't heard from my agent in about six months, so I called his office and asked, 'Has he died or something?' It turned out that he had died. I was so unimportant that no one bothered to tell me."

That's when David ended up with Joyce Selznick as his manager, after Selznick's dog, Shamus, bit him. He still reveres Selznick,who died almost two years ago. She got him his role as Snapper Foster in The Young and the Restless, and also one of the two starring roles in the Universal series, Semi-Tough, which lasted only four weeks. In 1981, he tested for three shows, T.J. Hooker, Today's FBI and Strike Force. He didn't get any of them. Since only one of the series survived, he probably was lucky.

Larson says, "I didn't pay much attention to David when Tartikoff's people sent him over to me. I had been testing one kid after another, and except for his height, he didn't seem much different in person. I sent a tape of all the tests to NBC and they turned everyone down. Then I looked at the tape myself. David's scene was one in which the electronic car was being explained to him. The look on his face and his tone of voice were perfect: 'You gotta be kidding me.' It was just what I wanted. I sent the tape back to NBC, saying,'What about this last kid on the tape?' They finally agreed with me, even though they had another, more serious guy in the running."

And so, at age 30, Hasselhoff became Michael Knight, Righter of Wrongs in a ridiculous, almost-human car. Why does the show work? Larson says, "The car brings in the kids; the adventure stories bring in the men - who mostly don't want to watch Dallas; David is so handsome that he has carried along with him a lot of the women in the Dallas audience who were his fans when he was in The Young and the Restless." It is with such so-called "demographics" that successful series are fabricated in today's television market.

As a result. Hasselhoff earns an estimated $15,000 per episode and lives in a unique Hollywood Hills house filled with hundreds of wind-up toys, which he assiduously collects and which distract his fiancee, the beauteous Catherine Hickland of the expired soap opera Texas.

On the show, Hasselhoff does not make things easy for his producers. The late Bob Cinader told me, "This kid comes in and complains it's ridiculous that the car gets more lines than the fine actor, Edward Mulhare, who plays Devon, Michael Knight's sidekick. What can we do? The kid's right. So he actually got us to slant a lot of the stories away from the car - which Larson wanted to do eventually anyway. The kid also violates all the rules of special-effects shows. He gives away our tricks to the press."

This undoubtedly is true. Hasselhoff blithely told me. "We use four identical black Trans Ams, not one; and when the stuntmen do those 50-foot jumps, a car sometimes breaks in half. Each of the cars has a protective outer shell on it. When a car gets banged up, they peel off the outer shell, like the skin of an onion, and the shell underneath makes Kitt look like new." Such irreverence toward state-of-the-art techniques is unknown or prohibited on other action shows.

On the other hand, Hasselhotf can get quite defensive about Kitt. Knight Rider will be scheduled at 8 P.M. (ET) on Sundays in the fall, but from time to time, NBC has seriously considered running it on Fridays against CBS's The Dukes Hazzard. It is fascinating to speculate about what would happen in a ratings war between the city car and the country car. Hasselhoff doesn't try to avoid the question. Outspoken as always, he says confidently, "No contest. Kitt is smarter. Besides, our scripts are better."

But then again, whose aren't?