Lively, hilarious Jamaica, where even the bamboo moves to a reggae beat

Jamaica is, as the advertisements say, not just a beach, but a country. A noisy, crowded, hilarious country. Inside that scalloped ring of white sand and warm, utterly clear water, there's a lot going on. Jamaican culture is assertive , which is not to say aggressive, but you should go there because you're interested in Jamaicans and a tan. Millions of radios thump out the curious, lagging reggae beat. And the lush landscape is not, by any means, unpopulated.

I was riding down the Rio Grande on a bamboo raft somewhere behind Port Antonio. Errol, my rafter, poled. Blue and white herons stroked across the sky. We came around a bend to find a lovely meadow on one side, a mountain on the other, with bamboo trees shaking like big green feather dusters in the wind.

''Zuguzugugu zuguzeng!'' boomed a loud, silly voice. The hills were alive with the sound of Yellow Man, a popular disc jockey, yakking his nonsense verses , which were pouring from a radio perched in the crotch of a tree, company for the peanut and drink vendor floating nearby on his raft.

It wasn't exactly the forest primeval, but it all went together. The music was happy, the bamboo was nodding, the river gurgled, and people did their laundry along the other bank.

They didn't get in the way of the mountains stacked with bamboo trees that creak in the wind, coconut palms, and pimento trees with allspice-scented leaves. In the midst of almost supernatural beauty, the slow bustle of Jamaican doings, full of song and dance, jokes and choice remarks, offers relief, sometimes comic. The Blue Mountains are so massive and, well, blue, they can make your heart ache. Until you see a row of nine-year-old boys in the foreground, moving like oil derricks or pawing the air like cartoon bunnies to the ubiquitous national beat.

It takes a few days of eavesdropping to understand the patois they speak here. It's English, but at first it sounds so foreign you don't bother to listen. Familiar words are disguised by accenting unexpected syllables. Figure out the rhythm, and you will be rewarded with what V.S. Naipaul called ''a Welsh feeling for rhetoric.'' It comes out in ordinary ways.

Mrs. J. Mullings, who runs the De Montevin Lodge with her husband, was talking about how she started to do the cooking there when her sister went to America. ''There was no one else to take up the -cudgel,'' she explains.

''Cool runnin's,'' yelled a group of men on the back of a truck loaded with bananas, meaning we could pass them. Beverly Hills, the walled, dog-protected preserve of the rich in Kingston, is ''stocious,'' or stuck-up, and a disagreeable person is ''hinky.''

The Stretch-to-Fit Club is the name of a bar, but it also describes an attitude. Just try to see light through a Jamaican minibus, packed with reggae-radio-toting riders as it lurches swollenly over the mountains.

If Jamaicans' sense of space stretches to fit, their sense of time is rubbery. You soon learn to ask for anything only once. It takes a long time to get it, but not because they've forgotten. I watched a hotel guest go into the kitchen to refill a coffee jug herself. She came back laughing, mimicking the cook's dance to the kitchen radio.

Watch someone walking home from the market in the noonday sun, under an umbrella, and you'll see the gait life in Jamaica takes. Try to walk the way you do at home, and you'll realize how sensible a gait that is.

Dr. Marco Brown, minister of tourism, says he aims for ''integration'' of Jamaicans and visitors. No problem, as they say here. The beach at Ocho Rios, a balmy crescent with skyscraping hotels at one end and a bauxite loading facility at the other, is an example of natural beauty spoiled by Jamaica's two big industries. But it is not just a playground for Chicagoans, Detroiters, and Bostonians. It is, especially on Sundays, a parade ground for Ocho Rians, who march up and down in bathing suits or Sunday best and umbrellas. It's a perfect place to get to know the town.

Going to the beach is a different proposition in Jamaica from the United States. Here, we try to get away from one another or at least pretend to be alone, braising in silence. Jamaicans clump together. Whole families sit in the shade of a sea grape tree. Dandling babies in the water requires several adults. People meet their friends, talk, and dance.

I was there the weekend of a Jaycee beach party. Under a palm tree, two five-foot speakers hooked up to a ''disco van'' whopped out reggae that must have set the seaweed jumping. Everyone danced. Bystanders absent-mindedly stirred themselves to the music, the way you'd tap a foot. Young boys showed off. Couples did neat steps at night, and by day toddlers shook chubby raised fists and nodded curly heads in rhythm. When a children's dance contest was announced from within the van, there was such a thick, intense crowd of onlookers, you'd have thought they were watching a prize fight.

But at nearby Dunn's River Falls, all you hear is water. The 65-foot waterfall is so full of freshets, cascades, frothing pools, natural slides, and splashes of sunlight, it could be a set for a Walt Disney movie.

Guides hired at the bottom escort you to the top, showing you where to play. ''Sit down. Bubble bath, no problem,'' said Lenny seriously. I followed directions and found myself neck deep in foam. It was like being a child with a very competent baby sitter. Looking up the falls, I saw I was not alone. Little groups of people were ducking behind falls, rolling off ledges, and sliding down chutes under the supervision of wise locals. ''Relax,'' they all seemed to be saying. A nursery school for tourists.

Port Antonio, to the east of Ocho Rios, is quieter, less developed, and more expensive. There are plenty of hotels here, but they're older, low-lying, posh places that don't interfere with the landscape. They are so self-sufficient, guests may only see the view on the way to and from the beach and don't turn up in town. Jamaica Hill is one of them. White bungalows rest on a pillow of perfect lawn in the hills - with a restaurant built around a tree, a nut cup of a pool, and a forested stairway to the beach. A week here costs $930 single, $ 703-$930 double. Manager Allan Gotting says, if you make under $65,000 a year, Port Antonio's not for you.

Maybe the Port Antonio of quiet hillside hideaways and private beaches is not for you. But stay in the De Montevin Lodge, a bed-and-breakfast that looks as if it had been hijacked from Edinburgh and plopped in a shabby genteel neighborhood , and downtown Port Antonio is all yours. Right now it is a real, unvarnished country town: dogs, pigs, and goats trot among human pedestrians, palm trees shade little cement houses in odd pastels, and the place gets purposeful on Friday and Saturday, market days. People from the country sell breadfruit, coconuts, gineps (a gooseberry-like fruit), and handmade brooms to shoppers from town. There's a move afoot to restore the gingerbread on the older houses, ban cars from the square, and paint the place up, but now it's an unretouched view of Jamaican country life, with public beaches up the coast.

The De Montevin Lodge's comfy, lace-bedecked dining room may look as if it's intended for off-duty shop assistants, bank tellers, and middle-management types , but Mrs. Mullings, who owns and runs it with her husband, cooks bountiful, traditional Jamaican food that lures all Port Antonio to her tables. She caters local weddings, and the town's parsons and teachers have their Christmas parties here. Even Jamaica Hill's resting executives come out of hiding for her dinners, and cruise ships send parties for lunch.

It must be quite a scene in high season, when tycoons, preachers, tourists, and traveling salesmen stop in to put away mounds of ackee with salt fish (the national dish, a starchy fruit that looks like scrambled eggs), pumpkin soup, rice dotted with kidney beans, chicken, curried goat, fried plantains, and plum pudding for dessert.

''Jamaicans like to have a good time,'' my guide says. When in Jamaica, do as the Jamaicans do, with the Jamaicans. Practical information

The De Montevin Lodge's 15 rooms are sparse but clean, with childhood photos of Prince Charles and Princess Ann on the brightly painted walls. Rates are $14 for a single, $25 for a double with bath, $12 and $20 without. Rates include meals. Lunch alone is $4.50 and up. Make a reservation if you are coming for a meal, and stick to it. Mrs. Mullings is as strict as she is talented. De Montevin Lodge, 12 Fort George Street, Port Antonio, Jamaica. Telephone: 993- 2604.

The Nonsuch Cave sits in a ridge above Port Antonio. With interesting limestone formations and oceanic fossils, the cave will delight geology fans. But its situation, on a ridge with a view of the Blue Mountains and the little bays of Port Antonio, a fresh breeze, and a brilliant botanic garden, makes it a worthwhile trip for non-spelunkers, too.