At least 70 buses, vans, and army trucks - with pedestrians and bicyclists threading their way between the mass - crawled up the hill into Xiangshan. I had intended to visit the villas, temples and pagodas of Fragrant Hills Park, but instead found myself awash in one of two monthly free-enterprise market days.

The market, I learned, was typical of those that had sprung up throughout China in line with the Government's ''pragmatist'' concession to capitalism and it drew people from throughout the surrounding county. From outdoor stalls that clogged a narrow cobblestone street no more than 20 feet wide, merchants sold silks, shoes, jade carvings, lace, fruit, liquor, live game and scores of other items. At one stand, I bought what was to become a typical lunch on the road (apple, sweet bread and a soft drink that tasted like liquefied bubble gum).

Pedaling back to Peking at around 4 P.M., I found that the day that had begun with a flurry of movement ended on an almost somnolent note. Along the way I passed a horse-drawn wagon with a load of firewood, its two drivers asleep in the back. Beside the road two students returning from school took to the train tracks, each balancing on one rail. Later, I overtook two teen-agers giving their girl friends a ride on the handlebars of their bikes.

Fortified by my first success, the next morning I steered into the heart of Peking. It has been estimated there are 3.17 million bicycles in the capital and that 500 per minute buzz through the busiest intersections; my own experience left little reason for doubt. Riding west along the rim of the city on Beihuan Road, then southward into the center on Andengmenwai Street, I shared the bicycle lane at times with five other cyclists riding abreast, as well as mule-drawn wagons and pushcarts. Everything with a motor ran alongside, in the adjacent auto lane, and most of it honked. The din of car horns and bike bells never ebbed; its very constancy sometimes gave the illusion of silence.

Suddenly, I realized I was the only person on a bicycle for three blocks and several hundred Chinese were staring at me; it was the closest waking equivalent I ever have had to my dreams of accidentally going to work naked. I had, it developed, ridden into an area of Wangfujing Street downtown that is off-limits to bicyclists. I dismounted, tried to dissolve into the walking crowd, and did not feel as if I had succeeded at it.

Whatever toll the gaffe took on my pride was outdone by the visual rewards I had already earned. Beihuan and Andengmenwai Streets introduced me to a city at work, where laborers laid sewer pipe in trenches dug by hand, where bamboo logs were lashed together to form the scaffolds for apartment construction, where parents queued for rations of meat, and their children followed day-care counselors along the teeming sidewalks.

I became the observed as much as the observer. My passing presence made schoolgirls titter, adults freeze into slack-mouthed doubletakes, infants spontaneously burst into tears and many bicyclists pull alongside to try to converse. I could answer them only with ''wo bu dong'' - ''I don't understand'' - but their persistence and parting smiles supplied a clear enough message.

From downtown Peking, I took a 10-minute jaunt to the Temple of Heaven Park, the likely place for any local to spend his day off. Riding through the park without any particular direction, I came upon a pick-up soccer game and soon was invited to join. The game was a loose affair that knew neither a set number of players nor specific boundaries; trees simply assumed a certain strategic importance.

By the time I dropped out of the match, having acquitted myself with what I considered a minimum of embarrassment, a crowd of kids had gathered around me. One of them, who looked 5 years old or so, began following me through the park and then, with wave of his hand, bade me trail him. Up and down the Temple of Heaven's steps we went, through the gardens, and finally over a five-foot wall, where, smiling at the devious beauty of his design, my young guide deposited me at our destination: a secluded bench where a couple entwined, necking.