He put the nop in the nop bop ba dee

Lester Lanin is a perfect gentleman, a wonderful person at a party. Just dance by and say "Tea For Two" and before you've finished your cha-cha turn, it'll be time to fox-trot. His band just eases into it. The music is smooth, the changes swift, and that casually elegant style -- both literally and figuratively upbeat -- gives everyone a feeling of well-being.

A tiny man, Lester Lanin is so eager to please that he never stops moving between the band and the dancers. I sat behind the brass one night at a Rotary Club dance and watched as he kept looking over his shoulder, checking the dancers' progress. He always knows what they're doing.

"I see their feet. If they're out of meter, something's wrong," he said. And he feels the problem lies with the sound he's producing, not with the dancers.

In this line of music, the customer is always right. Deference is Lanin's stock in trade, perhaps because his customers have included that segment of society most accustomed to being indulged. He and his orchestras have given the Rockefellers, the Fords, the Astors, the Whitneys, the Chryslers, the Du Ponts, and the Mellons just what they wanted. Royal families are coddled across the dance floor, and Lanin has sent accordion players to the birthday parties of at least three prominent dogs.

When something's out of whack, he adjusts the orchestra, much the way you'd tunea radio. He whirls around and holds up two fingers in the face of Julius Schwartz, the sax player, and then signs to the piano player. "Shh!" he says if they're denting the charm of the evening by starting out too loud. Or he'll clap his hands impatiently. Or point to someone and shake his head, or motion them closer to the microphone. Meanwhile, he's literally on his toes, hopping with excitement, glancing from dancers to saxophone to piano back to dancers, diving down to put his head to the amp to check if it's working, pouncing up to adjust an importune trumpet lick in the back row.

A tiny, thin man, he moves fast as a mouse. An elegant mouse in a tuxedo. He's so light on his feet you can see he'll have no trouble bouncing there all night, as he did all the night before at the Saint Nicholas Society Ball, one of New York City's most prestigious debutante balls.

He's been playing the ball for at least 40 years. "It's really gratifying that people are so loyal and book you," he says. "Junior Assemblies in New York , year after year. Junior League debutante parties. . . ." He's as much a requirement as white dresses.

Lester Lanin has been conducting bands since he was 15. He started out in the '30s, when big band music was at its heyday and "high society" was something besides the title of a Grace Kelly movie. He still uses the term today, calling himself a "so-called society band leader" just so you don't get the wrong impression and think he's bragging or anything. He's not a snob. He uses the term "society" to define a certain style of music and dancing:

"It's an up tempo. . . . 'Night and day, nop bop ba dee'" he sings, snapping his fingers fast, his hand clenched and bobbing abruptly to keep up with imaginary society steppers.

"The society dance is a quick step. Tsig, tsig, tsig, little one-step, you know. They never get tired, they can dance till six in the morning and then want more music, because they don't do anything. They just go straight ahead."

The reason he even says "society" is to differentiate it from his other jobs. Next month he's playing for the Longshoremen in New York, the night before he plays for the University Clubs of America. He plays conventions and square dances, Greek, Jewish, and Italian dances.

And, he explains to me, the Rotary dance won't be society. He doesn't care. He has music for them. "Tie a Yellow Ribbon 'Round the Old Oak Tree," maybe, or "The Beer Barrel Polka," and "In the Mood." Whatever it is, it all comes out smooth, classy, and bright.Lester Lanin music.

And the audience is charmed. Out there they are hopping and swirling and changing step with the songs. In their spring finery they look like a trayful of multicolored jelly beans being jogged to keep time to the music. And they please themselves. The smiles as they swing by are enchanting, whether they are dancing or just holding onto each other and walking rhythmically or hunching their shoulders in hopes of making a stylish impression. They look at the musicians and beam and you can tell they feel glamorous.

For the musicians, it's a matter of keeping together and "faking," which means managing harmonics and chord changes without music. They all have a repertoire of around 1,000 tunes, so when a couple swings by to request a merenguem (a rather saucy Latinate hustle) all Lester Lanin has to do is pick up his cowbell and yell out a title, and they instantly punch up the brass and pop out a Latin beat.

The atmosphere they create may be glamorous, but the work itself isn't. The musicians are all making hand signals to each other, drinking ginger ale when they can. (They hardly ever get a break. They are expected to produce, as if by magic, a steady stream of perfectly blended tunes.) Sometimes they look at me and roll their eyes, as the piano player did when Mr. Lanin pounced into the band's midst and slowed it down by putting his hand on the drummer's drumsticks. But mostly they just attend to the business at hand.

Basically, they are hustling. And, though the sound is flawless, they don't seem to do anything rhythmically, or even gracefully. As they hold up their fingers to each other to signify how many bars they're going to play next, they look as if they're on the floor of the stock exchange. A couple can come up and gush to Mr. Lanin and he'll turn to them, bowing deferentially and thanking them for the inevitable praise, and they play on without him. It's not that they're compensating for his goofing off. It's that they have different jobs.

The reason there are 30 Lester Lanin bands playing throughout the country at any time is that he is a great businessman, as self-effacing and charming to his patrons as a butler. He talks happily of converting boors into fure employers. Recently a man came up to Lanin as the soup was being served (a rare break, and then only because the headwaiter didn't want any soup spilled) and said he couldn't stand the music.

"Can't you play something slow?" he snarled. "So I said, 'I love to please you, sir,'" Lanin recalls. "So the next time I got up, I played a slow tempo, which isn't good for the majorirty of the people, and I saw that he didn't know how to dance at all. . . . But I am a servant of the public. I don't want him to come for an evening's enjoyment and make it miserable for him. So I went to his table and I told him the whole scene about tempos, about dancing, and at the end of the night, he wanted my card. He wanted to hire me for an engagement up north."

This attitude has worked wonders with everyone, from the Longshoremen to the Duponts. He has played at the White House several times. John Kennedy, he reports, "had back trouble, so he used to walk. He used to hold his hands high and walk. It was cute." Lyndon Johnson, however, was the best dancer. He liked country music, and had Lester Lanin over for dinner. And elsewhere, the Duke of Windsor used to dance all night, or until the Duches said, "Time to go home, Boysie."

Lester Lanin bobs all night between band and dancers. The band grumbles that it's not real music, that they only play a few bars of every song, but they're proud of their skill, their ability to stay together, keep an eye on each other and harmonize on demand. Lanin reaches in and tunes them, and people jounce by grinning, but they're staying tight, concentrating on each other.

"You watch him," says Ronnie DeMarino, the singer and guitar player, "He's trying to get each instrument to play exactly what's on his mind."

Another musicians agreed that Mr. Lanin has definite intentions about what's to be played, and though the band hardly ever gets its head, it has to be ready to shift at a couple of bars' notice.

Out on the floor, the couple who requested the merenguem tune are twirling dexterously all by themselves in a style that seems a bit alien to their New-England-businessman-and-wife look. She wears a nice high-collared brown dress with swingy pleats and has been to the hairdresser; he has on a good suit. They don't look casually elegant, they look dressed-up and excited. They're both a little chunky after the long winter, not the swivel-hipped disco fiends you would expect to do such a dance. Everyone else is in the buffet line or watching. And they're doing well, staying with the music and making fascinating patterns with their arms, each partner taking the right turn at the right time, like pros. They don't miss a trick. The improbable dance is charming on them, especially at the end, when they finish triumphantly, look up from their concentration to find that they're alone on the basketball court, and laugh.A magic moment. "Dee dee dee," hums Lanin commandingly, and the band swings into "Night and Day."