Personalities Are Split on This Isle : A visit to St. Martin reveals the distinct Caribbean blend of French and Dutch character.

Each Sunday, on the Caribbean island of St. Martin, the shops are closed and the churches are full. The Plage Naturiste--the nude beach--also has its following.

“Sunday is family day here on the island,” said Bernadette Davis, a cheery, 40ish native who has returned to St. Martin after living in West Africa and the United States. “You go to church and then you go to the beach.”

Not just the nude beach, however, but to any of 36 dazzling white-sand arcs on this breezy island with its intriguing split personality.

St. Martin is the name of the French half--the northern half--of the island, which lies 145 miles east of Puerto Rico. The Dutch half is called St. Maarten. To an outsider’s ear, the words sound very much the same.

My DC-10 from San Juan had landed at 10:30 p.m. at Princess Juliana International Airport on the Dutch side. My hotel room was 12 miles away in the pillared-and-pastel Le Meridien L’Habitation on the French side. Without flags, barriers or customs formalities, I was not aware of crossing the border as my taxi rambled through fragrant hills.

While the boundary is easy to miss--it’s marked only by a minor obelisk on a grassy rise--the differences become abundantly clear, even during a short stay. The French side is French in signs, in culture, in character. The Dutch side is more of a diluted, international blend. English is spoken throughout the island, although French and Dutch remain the official languages.

“A lot of our ancestors came from Anguilla and other English-speaking islands and so you see surnames like Richardson, Fleming and Davidson,” Bernadette told me as we toured the knobby island by van. “But schoolchildren on this side have all their classes in French.”

The big sport on the Dutch side is baseball. On the French side it’s soccer--plus a smattering of cricket, tennis, softball and squash. The only golf course on the island is at Mullet Bay on the Dutch side, although there are rumblings about a course on the French side and whether it might mean tearing down old sugar-mill ruins.

The only nude beach is on the French side--naturally--a wide swath of sand by Orient Bay. We parked near beachfront stalls where merchants--some of them clothed--were selling suntan oils, mirrored sunglasses and the cool cover-ups called pareos that are so much a part of French Polynesia. A sign near a sea-grape bush offered: “Nude Seven-Day Sailing Vacation, $850 a week.”

Although tourism is the major employer throughout the island, the Dutch side seems more commercial than the French: its hotels are big and sprawling; it boasts seven gambling casinos; superliners dock there.

The French side is more languorous. Hotels are low-rise and have a West Indies charm. The only legal gambling is cockfighting. Only smaller luxury cruise ships--such as the brand-new Royal Viking Queen--anchor off the port of Marigot and send passengers ashore by tender.

For electric current, the French side uses 220 volts; the Dutch, 110. And, although the island is no more than 15 miles from top to bottom, you must dial a foreign exchange to telephone from one side to the other.

The division of St. Martin/St. Maarten was firmed up in 1648 after a legendary walking contest. As a guide named Jacqueline Jones said in a lilting voice: “They stood with their backs to each other--the French man and the Dutch man--and then they started walking. The Dutch man discovered 16 square miles of the island, while the French man discovered 21 square miles. Now the reason why the French man discovered more than the Dutch is because the Dutch man stopped to rest and have a drink of the Dutch gin, while the French man kept on walking and had his refreshment at the end.”

Food and drink remain a big difference. Signs on the Dutch side are for Cafe Rembrandt and VanGoghstraat and Heineken beer. But the French side has long been heralded as the island’s dining room--and a gourmet haven for all the Caribbean. Resort guests and visiting yachtsmen hang out at waterfront restaurants in the village of Grand Case, where a bistro called Rainbow currently tops the jet set’s “in” list.

Philipsburg is the big city of the Dutch side, with parallel main streets named Front and Back. It has the island’s only traffic lights, and they are new enough to inspire confusion and jokes. Dutch duty-free shops specialize in electronics and cameras.

Marigot is the capital of the French side, its rues and boulevardes awash with fashionable names such as Fendi and Escada and Gucci. Shady sidewalk cafes could be along the Riviera.

Bernadette Davis, who now heads St. Martin Tourism, was born near mid-island in what is called Orleans, or the French Quarter, an area of old houses and set ways.

“There is where I went to school,” she said as we slowly drove through. “The teacher used to live upstairs and we had classes in the one room below. I walked everyday from my house and I would stop to pick guavaberries along the road.”

The Quarter is a place apart, even on this small island.

“Since we live next to the Dutch border we are Protestant like they are, instead of Catholic like the French,” Bernadette said with a smile.

“Look! There is the Methodist Church where I was christened. What a crowd they have this Sunday. They’re sitting all over the porch.”