There's A sparkle. It's almost like being in love. I don't know what it is. It just hits you," says George Clinton, the lead of the rock group Parliament Funkadelic, the morning after a successful performance recently in Milwaukee.

That special feeling, says Clinton, is what he has to get from an audience before he decides to do an encore. But when he gets it, that's it. After the Milwarkeeconcert, Clinton says, "I went all the way upstairs to my dressing room. I could hear the stomps and the screams from the audience. I was almost out of my stage costume when the road manager said, 'You can have 15 more minutes if you want.' "Well, then,' I said, 'let's go back and do some more." So, still dripping, with costumes covered in sequins, fox-tails and fringe, with enormous hats, wigs, Afros and sunglasses, the 12 members of the Funkadelic went back out. "We had already played everything we rehearsed," Clinton says. "So we just played our hit 'One Nation Under a Groove' again."

Theoretically, the encore is the treat, the dessert, for both performer and audience. As a practical matter, however, both sides of the stage have wised up to the other.

"You know perfectly well you're going to play an encore," says violinist Isaac Stern. "And they know you know you're going to perform an encore. And you know that they know that you Know you're going to do an encore."

And there are ways, Clinton points out, for performers to assure that one way or another there will be an encore. "A lot of people do encores out of ego. They do it even when people don't want it. Or they wald off stage and they haven't done their big hit, so you know they have to come out and do it for the encore. It's like part of your show. It's not your encore. It's planned. It's just done when people think the show is over."

Whether the encore is planned or spontaneous, however, the top performers always have a strategy mapped out beforehand The strategies differ, but they all deal with one problems-when to stop.

"You always play one less encore than the audience wants," says Stern. "You don't leave the audience surfeited."

"Regardless of what the audience reaction is," says soprano Beverly Sills, "I do two songs for the encore and I tell them I'm going to do two. I always go on the policy of leaving an audience wanting more."

"My father has an old saying," says Andy Gibb, whose hit album is "Shadow Dancing"; "Always leave them wanting more."

As for when a player decides to return to the stage, there is what Clinton calls the "tingle."

"You can feel an audience, you can feel their mood," says Stern. "You can tell by how many are leaving, how many are putting their coats on. You have to be stage wise. You can tell in the first three or four minutes of the concert what the audience is like. There's a certain flow of empathy front audiences."

"They've got to indicate that they really want it," comments singer Phoebe Snow. "Like stomping or cheering or a standing ovation." At a Washington concert a couple of weeks ago she found the audience so responsive - calling out requests and frequently bursting into applause - that there was little question about doing an encore. As Snow said later, "I would never let an audience like that get away."

It's not hard to decide when to play on, popular jazz musician George Benson says: "We just look out there and see the reaction. Sometimes we see people holding what look like candles or matches. All I can see is light."

For the Julliard String Quartet, there are complications in the encore decision. "We're having a running debate in our group," reports violinist Robert Mann. He and violinist Earl Cariyss have different criteria.

"He doesn't like to do an encore until we've taken the third bow," says Mann. "But I like to sense the mood. Let's say it's a late afternoon concert. Even if people have enjoyed it, they may want to just go home and have dinner. On the other hand, in the evening, everyone is feeling good, they're relaxed. Then, after the second bow, I think we should give an encora."

And Mana has his own personal measuring rod: "I tell by the quality of the silence as we play."

But there are some acts that just can't be followed. "When you have five guys who've just played the Trout Quintet," says pianist Andre Watts of that very well-known place of chamber music, "you can't do much for an encora."

Watts is currently performing saveral concerts in Washington, and he said he plans on giving no encores. "I'm playing so many concerts in Washington. I know they're met all on the same night, but I see them as a series."

Sometimes, Watts suggests, a player just ducks the issue, and, "The public need not be offended. If I'm not feeling well, I won't play. Why should I spoil a good performance by playing poorly for the encore?"

Other factors can also prevent the show from going on . . . and on. Phoebe Snow considered not giving an encore when technical difficulties plagued most of her Washington concert. As she sang close to the microphone, it continually shocked her on the mouth. But she did an encore anyway.

Orchestras and rock musicians alike must deal with the problem of music hall curfews. "We're on a very strict time limit," says Arthur Fiedler, the conductor of the Boston Pope Orchestra. "In Boston, the concert has to go no more than two hours."

"The halls we use have curfews," George Benson explains. "If we go over, the stage hands go on overtime, and the promoter starts paying more."

And there are times when the "tingle" just isn't there. "If they're not responsive enough," says Gibb, fresh from a 46-city tour, "I say, no way. I won't go back out. They just have to be loud enough."

Mistakes are made, however. Robert Mann said the quartet has performed an encore and then realized as they were playing that they probably should not have done it. "You realize you misjudged the crowd's mood. But if it's a short piece it's over soon."

The traditional way to start an encore is, of course, to leave the stage, wait as the applause continues, and come back out for a bow and an encore. "There's a whole ritual," says Sills. "One is off. One is back on. Then the house gives me a little bouquet. One puts the bouquet on the piano. WHile Charlie (Charles Wadsworth, her accompanist) get more music, I talk to the audience a little."

Some performers disdain the predictability of it. "During the applause (at the end of the show) I take some time to draw a deep breath," says Stern.

"You don't want to look as though you're scampering to start the encore before they can finish applauding. Sometimes if I'm on a particularly awakward stage to walk off, I'll say 'I know it's the custom to milk an audience for applause and leave the stage waiting for them to drag you back on, but it's a very long walk off stage, so if you don't mind, we'll play two encores and say good night.'"

"I don't like anything overly long," says Watts. "It's like playing another concert. I perceive the encore as a lighter kind of thing. When you've heard a long concert and you hear a Beethoven sonata for the encore, you think, 'Oh, dear, when is this going to end?' Sometimes I play small McDowell pieces, small Liszt pieces. At one time, I made a piano reduction of Bernstein's 'Candide' and played that like crazy for encores. If the performance ends with a blockbuster, knucklebreaker, virtuoso performance, I play something quieter for the encore."

But flamence guitarist Carlos Montoya, who is almost always be blockbusting, breathtaking guitarist for his concerts, saves sometimes even more dramatic for the encores.

"It is the story of the Holy Week Procession in Spain," says Sally Montoya for her husband who speaks almost no English. "There is a military procession called 'Saeta'," she says of a traditional religious and musical event that happens during Holy Week all over Spain but has become most famous in Seville. "Floats are carried on the shoulders of men, with the statue of the Virgin Mary and flowers. Then there is a band. On the guitar, Carlos does the music of the coronets and the drums and the entire band. It's very, very striking."

Snow Moes to plan it ahead of time. "And I want you to know," she says, "if they ask for something unexpected, we're in trouble."

When Fiedler performs an encore, it is so planned that the music has already been selected, placed in the musicians' folders, and specially made cards with the title of the piece have been cached on stage ready to be taken out and placed on the organ when the encore is performed.

Encores from the Boston Pope are usually reserved for audiences outside Boston who do not hear the Pops so often, according to Fiedler. But wherever they are, they are timed and selected to fit the time limit, because, "We can't play an encore that takes eight minutes if we have less than eight minutes left."

Silla, however, has sung the same encore for the past seven years. "I'm very fortunate," she says. "I havea Portuese folk song that my singing teacher arranged for me when I was 10 years old. She was my only singing teacher. She died seven years ago, and I dedicate the song to her."

Peter Nero, the composer and pianist, has a little joke he often plays on the audience during the encore. "I announced that in 1976 I was asked to put together a very beautiful love song. It's a piano solo. What they don't know is that it's a disguised version of the McDonald's them - 'You, you're the one - it's so subliminal. It starts slowly.

Then it gets carried away and ends off funny. You can hear a rumble go through the audience when they realize what it is. Other times for an encore, I try things that are new. That works out well. How can you lose? You've already finished."

When in Soviet Georgia, the Juillard String Quartet was given a volume of folksongs of Georgia by the members of the Georgia String Quartet. They decided to do them.

"In Russia they ask you for at least six encores," Mann says. "You haven't done the program if you haven't done six encores. If they love you, they love you all night." The group started the encores. When they got through five of them their arms felt tired. But they pursued. For the last encore they did the Georgian folksongs. "When they recognized what we were playing," recalls Mann, "it was like an earthquake, The audience applauded so much we had to stop. We couldn't go on."

In fact, when things have gone particularly well for a performer, it becomes harder and harder to get off stage at all. As Peter Nero says, "Sometimes it gets to be a game. The audience tries to see how long they can hold you."

Watts' says his solution is simple 'After two or three bows, I have them turn the houselights on and the stage lights off."

Stern is sometimes a little more forceful with his message. "If you want to stop the applause, you leave your instrument backstage when you come out for a bow. If they still won't quit, you leave the stage, put your overcoat on and come out again and wave good-bye. They laugh. You just have to give them a signal."