Pillsbury, Muffin, Cupcake and Cranberry aren't even aware that this is a momentous day. The little nuclear family of Barbary macaques -- father, mother, two- year-old daughter and one-year-old son -- is romping in its roomy cage in an off-exhibit holding area at the National Zoo. It's a typical monkey morning beginning with food, play and monkey-style communication with neighboring relatives Huckleberry, Blueberry, Strawberry and Mulberry. There are even the same familiar humans -- collection manager Lisa Stevens and three keepers.

"No nets," Stevens instructs the keepers. "If any of them gets away, it will probably be one of the young ones, and it won't want to go far from the parents."

One of the reasons for this pre-opening opening of Monkey Island is to show the keepers the escape routes, if any. The island -- a year and a half in the making -- cost $1.2 million and has a 25-foot bluff of boulders, hauled all the way from Burly Bottom, West Virginia, and a spectacular waterfall. It's been elaborately landscaped with loblolly and black pines, grass, red-stemmed dogwoods, even blueberry and raspberry plants. But no monkeys have ever set paws on it, and no one is sure exactly how they will react.

"The island is very much like their natural habitat," explains Stevens. "Barbary macaques come from Morocco and Algeria, and there's a colony of about 50 on the Rock of Gibraltar. The official name for them is Barbary apes, and, like apes, they have no tails. In the wild they live in large troops of about 20 to a hundred animals. We'll put these four out first and then integrate Huckleberry and Blueberry, who are sub-adult males. All of our Barbary macaques are related, but we're looking for new stock from breeding farms. Eventually we plan to have about 20 macaques on the island."

Barbary macaques' social structure requires the dominant male to meet challenges from would-be leaders. The bluff on Monkey Island will make a great setting for real-life games of king-of-the-mountain, and visitors will be able to observe these interactions from across a water-filled moat. Which brings up the practical question of whether macaques can swim.

"They can swim but we don't know whether ours will or not," answers Stevens. Just in case, there's an electric wire around the rim of the moat. And since the "island" is really a peninsula, the part that's connected to the land is sealed off by a high laminated-glass partition.

"Was the yard checked?" Stevens asks the keepers, who assure her that the island has been combed for safety hazards. Then the monkey-size door that leads directly from the holding area to the island is opened, and the wait begins.

"I don't expect them to come dashing out," Stevens tells a small group consisting mainly of zoo employees who have gathered to watch.

"You need some bananas out on the lawn," advises one.

"Do they realize how much money we spent on this?" asks another.

Meanwhile, keeper Diane de Graffenreid has gone down to the holding area to tuck the door flaps up so the monkeys can see what's waiting for them. The male, she reports back, is looking out -- but from the very back of the cage.

"There are about 25,000 Barbary macaques in the wild," says Stevens, with one eye on the door. Most are in Morocco where, while not considered endangered, they are threatened by deforestation and hunting. The small colony on Gibraltar are zealously guarded by the British army -- possibly because of the legend that says when the monkeys leave the rock, so will the British.

Just as most of the spectators are giving up and going to lunch, Pillsbury makes his move. He peers out, cautiously at first, then springs off a hillock and jumps almost to the top of the partition. The spectators gasp, but Pillsbury declines to do an encore. Instead, he looks around and sees a pine tree.

"He never had a tree before," says Stevens. But Pillsbury knows just what to do and climbs quickly to the top. From that vantage point, he looks down at the crowd and seems to yawn.

"He was greeting me," says de Graffenreid, and mouths encouragement in return. He's saying, "This is what I was built to do."

Once Pillsbury has climbed a tree and poked around the pine needles, it's only a matter of time before the family joins him.

"He's not making alarm calls, which would keep them in there," says de Graffenreid. "He could call them, but he'll probably go back and get them."

It takes several more forays and returns before Pillsbury finally emerges with the family, however -- with baby Cranberry on his back and Muffin and Cupcake close behind. Before long, they're all scampering up the rocks and eating grass.

"It's a pasture mix," explains horticulturist Ric Hider. "There are no toxic plants. We've planted blueberries and raspberries, and picking them will be a good manipulative exercise for them next summer."

For de Graffenreid, however, the Monkey Island experiment has already borne fruit.

"This makes all the years I've been here worth it," she says, watching the monkeys play. MONKEY BUSINESS

Monkey Island officially opens this Friday at 11:30, when zoo officials will open the doors and let Pillsbury, Muffin, Cupcake and Cranberry onto their new home. Thereafter, they'll be on view on the island daily from approximately 8 to 3, when they will go indoors to eat and sleep.