As China marks the 50th anniversary of Communist Party rule, not everybody is celebrating. Ask a wiry 20-year-old chef named Chen. He was walking to work on Sept. 22 when police arrested him, bused him to a detention center just off the road to the Great Wall and forced him to do what he does best--cook spicy Sichuan food.

"It was like we were maids," said Chen. "I would cook for them, wash their clothes, do everything."

Chen was one of thousands of migrant laborers caught in a pre-anniversary sweep of Beijing designed to rid the capital's streets of riffraff, beggars, ragtag laborers and anybody else who might take the shine off Beijing's National Day parade on Friday.

Chen's crime was not having the right papers to live in China's capital or work at the $100-a-month job that supports his wife and son in Beijing and the rest of his family back in Sichuan province. He was housed within the towering gray walls that surround the unmarked Heilongguan Custody and Repatriation Center, 15 miles north of the ornate Tiananmen Square rostrum where China's leaders have gathered annually since 1949 to celebrate the New China.

"Why are they arresting good people?" asked the soft-spoken chef, who was detained for seven days. "We don't rob or steal. All we know is work."

Still, using his cooking skills was better than being crammed into a cell and forced to crouch before the guards, he said. Being in the kitchen also freed Chen from the indignity of being beaten by a young boy who is a long-term resident of the center and hits detainees when the police tell him to. Once, when Chen stood up from his required squat because his legs ached, the boy beat him, he said.

More than 2 million people are detained every year under China's "custody and repatriation" system, which is used to control the flow of rural workers into China's cities, according to a report issued Wednesday by the New York-based group Human Rights in China. The group estimates that hundreds of thousands of people will spend China's National Day in more than 700 such facilities around the country.

Former detainees at Heilongguan said that those picked up with enough cash in their pockets--about $50, or a half-month's salary--are put on trains for an involuntary journey back to their hometowns. Others are forced to perform hard labor to earn credit toward the purchase of a train or bus ticket and can be detained for weeks or longer.

Chen had company in the kitchen. A half-dozen other detainees raised their hands when guards asked if there were any Sichuan chefs in the house, he said. Together, they prepared Chongqing Pepper Chicken, fish with chilies and garlic and pork in red-hot oil.

Xiao, one of the other cooks, was arrested the same day as Chen. He said he considers himself lucky to have worked with a wok. Other migrants were forced to break rocks at a nearby cement factory. He could also eat what the guards did not finish to supplement the four rubbery corn buns, piece of pickled turnip and cabbage soup that were prisoners' daily rations.

Guards released several of the cooks in Beijing today as a sort of National Day present. But Chen said he is not planning to watch the big army parade on television because he was upset by his experience.

CAPTION: A policeman questions a couple suspected of coming to Beijing illegally from rural China.