THE MUSIC, the splendor, the passions of opera are what lure many of its performers onto the stage. Not all its performers, though.

An apple or a carrot is a bigger lure for one cast member of "Porgy and Bess," now at the Kennedy Center. He's Brownie, the large, affable brown goat who pulls the crippled Porgy in his cart.

On a recent evening, Brownie emerged without fanfare from his van, which was parked at the Kennedy Center loading dock. After thrusting his head into a garbage can full of oats, Brownie nuzzled a visitor in search of either friendship or more food.

"You're dirty tonight," said caretaker Robin Seidon, as she carried him. Soon he would ascend to the stage in a freight elevator, let Robin and a stagehand harness him to a small cart that says "White Rose Soap" on the side, and await the arrival of Porgy and the first of his two entrances.

A stage goat's likes and dislikes are few but definite. Brownie likes carrots and apples, which make handy bribes. On the other hand, he does not enjoy walking past the orchestra pit on his way onstage.

"It scares him--he shies away from the opening," reports ensemble member Earl Baker, who handles the goat onstage. "He's a little stubborn at times, like most goats. So I show him the food in my pocket, and that gets him moving."

Jonathan Sprague, who is one of the cast's four alternating Porgies, likes to have a word with Brownie beforehand, to psych him up and calm him down. "I tell him, 'Come on, Brownie, you gotta cooperate tonight, you gotta come out and help me make a good entrance, just shoot right out there.' "

During the first act, Brownie is onstage only long enough to deposit Porgy. Even this brief stint must be handled carefully, since the goat has to continue far enough toward the front for the whole audience to see Porgy ensconced in his cart. Here Baker finds the tugging and steering skills he learned with a childhood pet goat useful.

"One night, right after his day off, Brownie didn't feel like entering," he recalls. "So he stopped very short and threw the Porgy forward. But usually he behaves himself. He won't move once he stops onstage, except for trying to get into my apple pocket or pulling on my suspenders."

An hour or so later, the opera is ending. Bess has departed for New York, with Porgy determined to follow her. "Bring my goat!" he thunders. On walks Brownie with the cart, looking calm despite the storm of emotion raging around him. As Porgy and neighbors burst into "I'm On My Way," Baker scratches his charge behind the ears.

Brownie belongs to the Dawn Animal Agency and lives on a New Jersey farm. So far he has seen the bright lights of Chicago, New York, St. Louis (whose small stage scared him) and Washington with Porgy and Bess. New Orleans comes next. He should stay with the company while it tours other cities, but animal quarantine laws make it unlikely that Brownie will ever play Europe. "When the last Porgy toured abroad, we had a new goat in every city," sighs goat-handler Baker. "That was something else."

And no matter how good he gets, there are no greater operatic roles for Brownie to covet. "Porgy and Bess" is it for operatic goats--as is "Aida" for elephants, Wagner's "Ring" cycle for noble steeds, "Der Rosenkavalier" for fancy little parlor dogs. Some Porgy productions omit the goat if things get too expensive or complex, making a good goat gig rarer still.