She was a superstar singer-actress of the People's Republic, a Chinese Judy Garland who hobnobbed with national leaders and received six times the salary of an average worker. Then suddenly, in 1967, she was a political prisoner, her hair turning gray, her voice weakening, forced to leave a son born just before her detention.

The woman is Yuan Hsueh-fen, now an earnest lady of 55 who, by telling her story to an American reporter visiting this huge Chinese port city, become perhaps the first victim of political persecution in the People's Republic of China allowed to discuss her case in detail with a foreign journalist.

Yuan's troubles, and an unusual official effort to portray them as a miscarriage of usually humane Chinese justice, say much about a country whose human-rights record has become a source of debate in the United States.

American critics of the move toward full diplomatic relations with China say Peking utterly fails the Carter administration's own human-rights test. Yuan's story, however, reveals some surprising paradoxes.

Yuan is able to talk now because the politicans who jailed her for three years and forced her into professional limbo for a decade have been thoroughly discredited and purged from office. Her adversaries were what the Chinese now call the "Gang of four" - Mao Tse-tung's widow, Chiang Ching, and three top Shanghai administrators.

Yuan's anger over what they did to her aid to her old friend, the late Premier Chou En-lai, provides a startingly candid view of the facts of political life in China during the past 10 years.

"They kept a close watch on me," she said. "I was in Shanghai, the most closely controlled place in China."

The three-hour interview with Yuan and two other victimized Shanghai performers, arranged completely on the initiative of the Chinese authorities without any request from The Washington Post, reveals problems in the practical application of Mao's call for rehabilitation of wrongdoors through reason, not through force.

Admirers of the Chinese system will be impressed that even in Yuan's case, Chinese interrogators honored their street strict rules against torture of the thumbscrew and electric-shock variety.

Yet Yuan and forced to undergo perhaps 500 separate interrogations at various times of day or night for three years. She was put in numbing isolation and under severe psychological pressure without formal indictment or chance of appeal. Critics of China will find it chilling that Yuan today i not so critical of the treatment, which is standard procedure for Chinese recalcitrants, but that it was meted out before she was tried and sentenced under proper Communist party procedures."

Yuan was a political movie of beauty and talent who was delighted when the party offered her an honored place in post-liberation China. But she had trouble keeping up with the shifting party line in the arts.

Even before 1949. Yuan had received acclaim for her for performance in the Shaohsing Opera, an immensely popular folk opera given to melancholy songs and tales of lost love.

Chou En-lai - her future patron and eventually the indirect cause of her imprisonment, first saw her when he sneaked into a performance in Shanghai in 1946 while dodging Nationalist intelligence agents.

"I didn't know when I was on the stage that he was there," she said. "At that time I was very young. I was a young actress and I didn't know my politics . . . I was dissatisfied with the KMT (Nationalist) persecution of us, but I did not know the Communist Party policy."

When the Communist finally took over in 1949. Yuan was welcomed into the party for her talent and for her courage in acting in some politically tinged dramas unpopular with the KMT authorities. She was elected a delegate to the National People's Congress. China's Parliament, in 1954, 1959 and 1965, and her salary was soon at the upper party level - $163 a month.

Popular as Yuan was, she was in a vulnerable position in 1966 when Mao decided to attack the encrusted party bureaucracy and less than revolutionary aspects of the arts.

Shaohsing Opera was full of what could be considered bourgeois sentimentality and traditionally all the parts had been played by women, something the Communists soon changed. That, plus Yuan's popularity and friendship with Chou. Chou's wife Ten Ying-Chao, and foreign minister Chen Yi - all people considered adversaries by Chiang Ching's allies - eventually led to her imprisonment.

"The Shaohsing Opera is entirely bourgeois," Yuan quoted her critics as saying in 1966 at the beginning of the Cultural Revolution. "We have to make investigations to see who is behind the development of a bourgeois local opera."

"They meant to collect blacklist materials on Premier Chou." she said. "They took away all my notebooks and my letters written by Premier Chou and Ten Ying-chao to me.

There are some photos of the two with me, and they said these were evidences of my crime. They accused me of being a member of a certain KMT organization . . .

I was branded a bourgeois element. A rightist and a counter-revelutionary."

Yuan was put in a large mansions in the southern part of the city, locked by herself in one room. She estimates that at least 20 others were detained there in separate rooms, including professional storytellers Tang Ken liang, who joined her in the interview.

"We were neighbors at that time," said Tang, with a laugh.

A relative whom Yuan had asked to take care of her youngest childest born in 1966 was branded a landlord and the child had to be turned over to a maid. Her husband, a newspaper reporter, was forced to attend a work farm and then work as an editor in a publishing firm against his will.

She was not allowed to see her family for four years. While under detention," I slept in my coat because I didn't know when I would be interrupted. They were always cursing me. They demanded that I write so-called confessions. I didn't count the number, but they probably held accusation meetings of her about 500 times. It was impossible to study Chairman Mao's works, so I couldn't understand the policy-line struggle. But I stood steadfast."

In 1970, she was released to a work farm and allowed to see her family one once or twice a month. In 1972, during an investigation of her case, one cadre said: "I have studied Yuan II-sueh-fen's case many times. we don't have anything aganst her. We should liberate her."

But the advice did not please Shanghai Mayor Chang Chun-chiao, Yuan said. In a hint as to who was in command in Shanghai during the last decade. Yan said Chang bluntly told Premier Chou, his political superior, to "Keep his nose out" of Yuan's case he enquired about it.

In 1973, she was cleared of all charges but not allowed to perform or to reveal her identify to the few voice and acting students she was allowed to tutor.

"I am an actress and I should practice the singing every day," she said, "but for 10 whole years I couldn't sing a single song of Shaoshing Opera."

When Chou died in early 1976, without Yuan seeing him again she said she collapsed in grief and remained half paralyzed in bed for some time.

But in October, when Chiang, Chang and the other members of the "gang of four" were purged by new Chairman Hua Kuo-feng, "My illness went away and I joined a parade in celebration."

When asked question about human rights, Chinese spokesmen argue that 95 per cent of Chinese have full rights. The remaining 5 per cent, the bad elements, don't deserve them, they say.

Martin Ennals, secretary general of the London-based human-rights organization Amnesty International, says his group had not published a report on political prisoners in China. "One of our problems has been we felt the Chinese prisoners would not be helped by pressure from abroad," he said in an interview.

Like almost everything else in China, policy toward human rights is a paradox. There is probably far more repression than visitors see, no concept of fair trial, extremely harsh sentences.

The paradox comes in lower levels. A visitor is impressed by the degree to which the average man in the streets talks back. The wall posters are part of that. If a policeman screams at a cyclist, the cyclist will scream right back.

If one accepts Marxist Leninism, there is room for free speech in China. But open rejection of that creek is a violation of the law and punishable by imprisonment. Whether Yuan's story heralds, a softening of that line remains to be seen.

She is singing again, despite the fact that "I'm physically weak and getting old." But she says she will not forget the day she first met her son, already for years old, after her release.

"When I called him, when I called him the first time," she said, "he stared at me.Later he embrace me and cried."