Considering that her father had been a compulsive gambler who frequently spent the family's rent money and that she had never felt any affinity for games of chance, Vivian Bush seemed an unlikely candidate to succumb to the blandishments of a magazine ad that read: "Learn to Play Blackjack and Make Money."

Bush was earning a decent income as a bartender in New Jersey at the time, but there was something about this pitch and its money-back guarantee that struck a responsive chord in her. At the time, she didn't even know that blackjack schools are legitimate, and that blackjack is the one beatable casino game. Even so, she headed across the country to spend four days under the tutelage of an expert named Stanley Roberts.

"Having no prior knowledge of the game," Bush conceded, "I was totally boggled." But Roberts drilled her incessantly in the mechanics of card counting, the technique that revolutionized the game and the whole casino industry.

In the 1960s, a mathematics professor named Edward Thorp had shown, through the use of a computer, that as various cards are played and the composition of the blackjack deck changes, the odds can shift into a player's favor. By keeping track of the ratio of high cards and low cards that have been dealt, the player can recognize these favorable situations and bet accordingly. But it's tough work.

After studying with Roberts, Bush came home and spent hour after laborious hour dealing herself blackjack hands, turning herself into a virtual card-counting automaton. A month later, she paid a return visit to her teacher. She recalled, "He dealt out the cards fast . . . he'd ask me how much to bet . . . he'd ask me why I'd make a particular play. And then he said, 'You're okay. Go to the casinos and start making money.' "

Bush went to Las Vegas with a $400 bankroll and followed all of Roberts' precepts. She played in short stretches at different casinos to avoid attracting too much attention. Occasionally, she made bold unconventional plays that the system demanded -- like hitting a 17 against a dealer's ace. But mostly she settled into a businesslike routine, and after 10 days she had built her bankroll to $4,000. "It was like a fairy tale," she said. After working as a legal secretary, a real estate agent and a bartender, Vivian Bush had found her calling.

When Atlantic City legalized gambling, Bush started playing there, and was soon forced to confront the problem that confronts every blackjack expert. The system that card counters use is probably the only gambling system ever devised that really works. For players with the proper temperament, patience and mathematical bent, it can be almost as reliable as an annuity. But the Catch-22 of the system is that the casinos will arbitrarily bar successful professionals from playing, so that keeping a low profile becomes more important to the card counters than the game itself.

"Being a woman," Bush said, "I had some advantages. They tend to assume that you're a dumb broad. For example, splitting 10s can be a very sophisticated play or very amateurish, but when I did it I'd say, 'Oh, I just have a hunch,' and I'd get away with it because I was a woman.

"At Atlantic City in the beginning, card counters could play. But pretty soon the heat got to be the worst in the world. They want no winners whatsoever. They were seeing me four times a week and they were remembering me. One day at Resorts International, the lights came on -- it's usually dark in the casino -- and the eye in the sky took my picture. The next day, I was playing for 10 minutes and the security guards came over and said, 'We've determined that you are a professional card counter.' "

Cut off from what had not only been a reliable source of income but also a passion of her life, Bush did the things that many other card counters do. She used subterfuge. She employed disguises. And then, like her mentor before her, she decided to open her own blackjack school.

The growing number of schools that teach blackjack don't really offer anything unique; they are all promulgating essentially the same system. A would-be player could learn the technique by spending $3.95 for a paperback edition of Edward Thorp's book rather than $495 for Bush's personal instruction.

But Bush said, "Very few people can get it from a book, even though our students are mostly professional types with at least a college degree. We use flash cards and other teaching tools and we provide a very strong support system. We try to teach them to deal with the emotional side of the game and to handle themselves properly at the table."

Just as her own teacher had done for her, Bush will periodically tell her students, "Go to the casinos and start making money," and some of the gifted ones will probably do it until the casinos throw them out. Then they, too, can join the growing ranks of card counters with a wondrous skill that they are not permitted to employ.