THE public beaches are often packed like a bus at rush hour, so that sand is scarcely visible through the carpet of towels and sizzling flesh. But then again it would be a grave mistake for a foreigner to go to Beidaihe in China in search of the perfect beach. Asia's greatest beaches are in Thailand and Malaysia, and Beidaihe's are too northerly, narrow and crowded to qualify for world renown. So a trip there is more about China-watching and people-watching than tanning.

Beidaihe (pronounced bay-DIE-huh), on the Bohai Sea 170 miles east of Beijing, is China's most famous seaside resort. Every year from June to September some five million tourists, mostly Chinese but including foreign diplomats, journalists and business executives who live in China, pass through for sun and sand.

Much of Beidaihe's fame derives from its special status as the site of the annual power struggles among China's top leaders. It is a bit like a Camp David for the Chinese Politburo, but even more important: party elders no longer attend the Politburo meetings in Beijing and almost never see each other face to face, except when they are nominally on vacation in Beidaihe. As a result, the key strategic decisions on China's future are often made not in the capital but in the summer homes of the top leaders.

Foreigners living in northern China discovered Beidaihe's beaches and began to turn it into a beach resort in the 1890's. They oversaw construction of a railroad link with Beijing to make it accessible, and they began building summer cottages along the beach. These were burned down in the Boxer Rebellion at the turn of the century and then rebuilt in much grander style.

Even today many of the finest mansions of Beidaihe are in a colonial style that points to their origins before the 1949 Communist Revolution. Belonging to foreign embassies and companies, they were seized by the regime and turned over to political leaders and Government ministries. Now equipped with air-conditioning and high stone walls to keep people from peering in, scores of these mansions -- which would not be embarrassed in a beauty contest with multi-million-dollar estates in America -- are the domain of the Communist Party.

Elderly party officials enjoy the exclusivity of their private beaches, guarded at each end by members of the People's Armed Police seated on folding chairs on the sand. On the public beaches middle-aged couples encased in acres of swimsuits lie back on their towels surrounded by piles of food. And little children play naked in the water while young people prowl about in Western-style swimming trunks and "san dian shi" -- "the three-point style," meaning bikinis -- in a courtship ritual not so different from the one to be seen in, say, California. Away from the beach, visitors can spend the evenings dancing or singing karaoke in nearby bars. There are also tennis courts and jogging paths.

With a year-round population of only 55,000, Beidaihe is reasonably compact. It is easy to get around on foot in the beach district, strolling from Kiessling's Pastry Shop to the cafes to the beach and back again. There are very few cars and bicycles, so it seems particularly somnolent in comparison to other Chinese towns.

In 1992 the authorities opened a new tourist site in Beidaihe, offering visitors the first opportunity to see how China's leaders live. It is the former summer home of Lin Biao, the army leader who died in mysterious circumstances in 1971 after apparently trying to stage a coup against Chairman Mao Zedong. Lin, who was then the second most powerful person in China and Mao's designated heir, is said to have been killed in a plane crash in Mongolia after fleeing when his plot was discovered.

Lin's home, which has been empty since his death, is a fascinating window into the world of the Communist leadership. Normally the leaders live behind high walls, and descriptions or views of their homes are almost never allowed in the news media; even the locations of the homes are state secrets. Even now Lin's villa is not mentioned in any of the tourist literature, and only a paper sign in Chinese marks the location inside Lianfengshan Park.

The ticket woman took my 2 yuan (the equivalent of 37 cents) without interest, and I joined the hordes of Chinese tourists going through the 20 or so rooms of the mansion. Like most places in Beidaihe, the Lin home is closed outside the June-to-September tourist season.

A large gray-brick two-story house, set in the woods and surrounded by trails, the villa has a garage at one end and a 70-foot indoor swimming pool at the other. Upstairs is a solarium. Unfortunately, all the furniture is gone and vendors have moved into most of the spacious, high-ceilinged rooms. Lin's master bedroom is full of hawkers selling seashells.

Just below Lin's house is a small wooden pavilion. If you brush by the policeman sitting in it and look in the opposite direction from Lin's home, you will see, about 100 yards away, the red tile roofs of a huge mansion once used by Mao. It is now occupied each summer by Deng Xiaoping, China's senior leader. "When the leaders come, it's martial law around here," said a taxi driver who took my wife, Sheryl WuDunn, and me around for two and a half hours for $15.

Each July and August, when the top leaders are in town, policemen are stationed all along the beach and throughout the town. When I went jogging one morning, I ran by a man in a T-shirt standing by his bicycle. Just at that moment a walkie-talkie in his back pocket began blaring, revealing that he was a plainclothes policeman.

"Do any of you have a fruit knife?" a policeman asked a Chinese friend when he stopped her and a carload of her friends at a roadblock near the leadership compound. Thinking that the policeman had an apple he wanted to peel, several offered their knives. He confiscated them all.

Above Lin's house in the woods of Lianfengshan Park is a more traditional sight: a jewel of a temple, several hundred years old, dedicated to the Chinese goddess of mercy. Destroyed in the Cultural Revolution but later restored, the quiet temple and its rustic courtyard draw a steady flow of faithful, mostly older Chinese.

They offer small contributions to the statue of the goddess, Guan Yin, and light joss sticks to bring good luck and to have their prayers answered. Guan Yin, whose role in Chinese culture is sometimes compared to that of the Virgin Mary in Roman Catholicism, is one of the few Chinese divinities who is not supposed to be presented with the standard offerings of wine and meat.

The other principal park in Beidaihe is the much smaller Pigeon's Nest, a dozen acres with a natural cave meandering through a hillside. Above is a statue of Mao -- a rarity in China these days -- to commemorate a poem he wrote in the 1950's about the town's fishermen.

A pavilion on the hilltop overlooks miles of coastline and scores of resorts for China's "new class" of Communist elite. It's a delightful place to compete with Mao in writing verse, or to simply enjoy the sea air. PLACES TO STAY, PLACES TO EAT Getting There

Trains leave Beijing every couple of hours for the four-hour to five-hour journey to Beidaihe. A "soft seat," which is comfortable and reserved for foreigners and Chinese officials, costs $14 each way. Your hotel in Beidaihe can book a round-trip ticket. The best time to visit is May to September; in winter Beidaihe is deserted. Accommodations

The best place to stay is the Beidaihe Guesthouse for Diplomatic Missions, run by the Foreign Ministry. It overlooks its own private beach and has a decent restaurant and a clay tennis court. You should reserve and pay in advance ($54 for an air-conditioned room with two beds). The Beidaihe telephone number is (335) 441-287; the Beijing office is 532-4336.

Another decent hotel is the Jinshan, 441-338, also with rooms at $54. Take American dollars, Chinese currency or traveler's checks, as credit cards are not commonly accepted in Beidaihe. Getting Around

A taxi costs $6 an hour for a tour, but few if any drivers speak English. Some Chinese on the beach will speak English, however, and may be willing to guide a foreigner either out of a sense of friendship or for a small fee. Dining Out

The hotels all have restaurants, and there are plenty of private restaurants around town. They specialize in seafood, and a meal will cost $10 or less a person, sometimes much less. What to Take

Take your own suntan lotion, as it is not easy to find in Beidaihe. Beach umbrellas can be rented for $2 a day, and beach towels can be bought from many small vendors.