Some things are forever. Brooklyn, for example. Sidney Shapiro, of Flatbush and Peking, hopped a freighter one day in 1947 with a heart full of romance and a wallet considerably less endowed to set sail for China. Thirty-seven years later he is a citizen of the People's Republic of China -- and he still sounds like a kid from the neighborhood.

"When I first began living and working in China, there were very few Americans," Shapiro says. "But there were Pommies and limeys and Australians. It was frightful. It began corrupting my good Brooklyn accent. It really affected me accentually."

He is sitting in a vast sitting room in the Chinese embassy looking distinctly preppie: blue blazer, white shirt, striped tie. Only the black Chinese sneakers give him away. He could be anyone's American uncle, this author and translator who has spent the better part of his adult life becoming Chinese. He is at home here, but then again he's not. Ask for him by name over the telephone and you may be told, "So sorry. Wrong number. This is the Chinese embassy."

He has come for a three-month visit, to see his sister in New Jersey and to promote his new book, "Jews in Old China, Studies by Chinese Scholars" (Hippocrene). Shapiro translated and edited the collection of essays tracing the history of Jews in China as far back as the 10th century A.D. By the 19th century they had all been assimilated, he says, by a culture that knew no anti-Semitism. There are some Jews living in China today, mostly foreigners. Shapiro says he is not the only Jewish citizen of the People's Republic of China. "There's another guy," he says. "Izzy Epstein."

This is his seventh trip to the United States since leaving for Shanghai in March 1947. The first time he returned, in 1971, he flew to Canada and had to get a visa from the American embassy in Ottawa. There were no diplomatic relations between Washington and Peking then. "I said, 'I need a visa to visit my old Jewish mother in Brooklyn,' " he says. "They said, 'Buzz off.' So I pulled out my passport and said, 'It's true. I really am a Chinese.' "

There was culture shock at the violence and blatant sexuality ("bottoms and bosoms on magazine covers") of the society he had left behind. Now it seems worse. He senses an increase in anti-Semitism since his last visit, in 1981. He believes the American economy is in trouble. Last week he bought two turtleneck sweaters at B. Altman's in New York only to find that they were "Made in the People's Republic of China." He also bought a cordless telephone made in Taiwan.

"I'm comfortable here," he says, "but I'm also comforted knowing it's only going to last two or three months. I can't explain it any better. I gorge myself on all the nostalgia things, the lox, the sturgeon, chocolate-covered halvah, the pastrami sandwiches. Two years ago, a justice of the Supreme Court of New York brought me a half a pound of Zabar's smoked salmon, caught in the streams of Scotland. Fancy stuff. It was all packed around in dry ice. I do get care packages.

"It's funny when I'm here and I commute from Jersey every day an hour on the bus. I get to the Port Authority building, walk to Madison Avenue, sit at my desk and talk on the phone. It feels great, you know. This is what I was doing 40 years ago. I feel comfortable and confident at it. I like all the excitement. I have a little high blood pressure. I was sure it would zoom up in the stratosphere, but it went down. I haven't even caught cold. It just shows I've been too lazy in my life in China. I've had it too easy maybe."

He is 69 now and beginning to have problems with cataracts. He says there are no regrets, no idle thoughts of what might have been. "That's what I was afraid of," he says. "That I'd become a successful theatrical or corporate lawyer, married to a Jewish princess, living in a snug little suburban house with an electric lawn mower."

He was a young lawyer with a degree from St. John's University and no desire "to spend the rest of my life representing people who were trying to outsmart other people and make money at the expense of other people. I didn't want to be the intermediary, the overseer of such things. I was idealistic then. I'm idealistic now. That's what kept me in China."

He was an idealist, not an ideologue. He voted for Franklin D. Roosevelt in 1944. Friends had gone to Spain and lost their lives fighting fascism. He didn't. He went to China "out of curiosity, and I remained out of curiosity.

The U.S. Army had taught him the rudiments of Chinese and some history and geography. Though his training was never put to any practical purpose, Uncle Sam had kindled a spark. Shapiro left New York with $200, a duffle bag of Army surplus goods (hoping to make a killing on commissions) and a promise for work as a stringer for Variety (he had done some theatrical law).

One of the first people he called, a friend of a friend, became his wife. Her name is Fengzi -- Phoenix. She is an actress and drama critic. Their daughter is a doctor married to a doctor. Their grandaughter is named Pervading Fragrance. They all live together in Peking.

Things were not always so idyllic. His wife was editing a magazine directed by the communist underground when they met. She was more political than he. When the forces of Chiang Kai-shek began to take an unhealthy interest in her, they decided to join the communists in the liberated zone. Together, they witnessed history. Shapiro was in Tienanmen Square in Peking on Oct. 1, 1949, the day Chairman Mao Tse-tung made his famous speech declaring China a communist state. "I was in it," he says. "I was more and more in it. I became less of a spectator and more a participant."

He had a brief fling as a movie actor, playing Americans in Chinese films (his wife called his acting "vapid"). He worked as a translator of Chinese literature for the government's Foreign Languages Press for 36 years until his recent retirement. His autobiography, "An American in China," was published in America in 1979. "Good, bad or indifferent," he says, "no one else had the chutzpah" to attempt a review of modern Chinese history in 280 pages.

He anguished over the Korean war but supported the Chinese. "What America was doing in Korea was disgraceful, indefensible," he wrote. The tone of the book is sometimes polemic. He is softer in person, sipping his tea. "Real Chinese tea," he says. "Not the stuff you get in Chinese restaurants."

In 1963 he became a Chinese citizen. "Well, I'm not a Communist," he says. "I'm trying to be a Marxist, but I'm not doing so good. Let's say I'm a Chinese Marxist. Obviously, I think they are on the right track."

He wasn't so sanguine during the Cultural Revolution. It was an unkind time for many Chinese, including his family. His wife was sent away to be rehabilitated for unspecified crimes. They saw each other by his count three or four times in four years. The visits, he says, were great favors to him. "I couldn't quite believe it," he says. These were not the Chinese he knew. "I kept thinking, 'It can't last much longer, in six months she'll be home.' Three months became six months, and six months became a year. It got to be four years before she finally returned for good."

He was properly indignant. "I couldn't even find out what she was supposed to be accused of. Nobody knew. I wrote letters to Chou En-lai. Before she went off to the camp, I went to see her at her office every night. I asked these guys, 'What did she do?' They said, 'Orders from above.' The orders from above was Mao's wife, who was making preemptive strikes against anyone who she thought knew some of the details of her predilections for light wines, boys and young men. You see, she and my wife were in the theater, though not the same troupe.

"A lot of our friends were detained, a few were imprisoned and one or two murdered. So we got off easy. There were a lot of ardent, born-again young Chinese who felt they were being very patriotic. They were quite sincere. These were the kids who became China's lost generation. After the Cultural Revolution, they found they had been had. All of the ideals for which they sacrificed their schooling -- no one went to school or learned skills -- and at the end of the Cultural Revolution they were 25 or 30 and knew nothing. Ideologically, they had been sold a bill of goods. That's one of the problems we have to solve now. It's not easy."

But life is good. He has learned to make sesame bagels. He has 200 tape cassettes of Bing Crosby, the Supremes, Alberta Hunter, Beethoven and Baroque music. Though they get a lot of foreign films on Chinese television, he still misses Woody Allen and the Marx Brothers. "Michael Jackson? The black singer? They've never heard of him. Prince? Even I haven't heard of him."

Despite this cultural lapse, he leads, by Chinese standards, a luxurious existence. This embarrasses him. A few years back, at the Foreign Language Press, he tried to get the government to reduce his salary. It refused. "I just didn't think I was worth all of that," he says. "My status is foreign expert, so I get all the perks."

He retired with full pay, 600 yen or about $300 a month. "A starting factory worker might get one tenth of that," he says. "It's also double what the highest paid university professor or scientist or minister of a department would get."

Last year he was named to the Chinese People's Political Consultative Council, a national advisory board that he describes as a shadow congress, which proposes legislation and policy changes. The Chinese value and encourage his foreign contacts. He has become a cultural emissary.

He says friends here envy the intrigue of his life. He doesn't see it that way. He remembers riding the rails during the Depression with a friend. One day in New Mexico, chasing a westbound freight, he tripped on a switch and missed the train. His friend went on to California. He went home. "We did some very stupid, very dangerous things," he says. "We were warned by the professional hobos to stay away from certain towns, that the yard bullies would beat us up, throw us off trains. We'd look at each other and say, 'Oh, these guys have been seeing the wrong movies.' We couldn't believe all the danger and excitement going on.

"I think probably I've lived my life in China that way. It just seems part of the normal progression."