The government did not immediately issue a statement. But the state-run media said Mr. Yao died of diabetes. It did not specify where he died.

Mr. Yao was a former Shanghai journalist and propaganda official whose writings and association with Jiang Qing, the wife of Mao Zedong, and two other colleagues -- who together formed the Gang of Four -- was blamed for helping touch off one of the darkest periods in China's modern history, the Cultural Revolution, a period from 1966 to 1976 when China devolved into social and political chaos.

At the height of his power, Mr. Yao was a member of the country's ruling Politburo and was feared for his lethal essays. He was even dubbed the killer by pen.

He wrote an essay in 1965 that was later considered one of the opening salvos in the Cultural Revolution.

Later, according to the government, he admitted to falsifying evidence that led to the purge of Deng Xiaoping, who was rehabilitated in 1976 and went on to become China's top leader.

After the death of Mao in 1976, however, the Cultural Revolution came to a close. Mr. Yao, along with Madame Jiang and their two Shanghai colleagues, Zhang Chunqiao and Wang Hongwen, were arrested, subjected to public show trials and sentenced to long prison terms for their role in framing and persecuting hundreds of thousands of people and throwing the country into violence.

Madame Jiang, the leader of the Gang of Four, is believed to have committed suicide in prison in 1991. Mr. Wang died in 1992, and Mr. Zhang died last April in Shanghai at the age of 88.

Mr. Yao, who was released from prison in 1996 after serving a 20-year prison term near Beijing, was reported to have been living in Shanghai at the time of his death, writing a book.

Mr. Yao, born in 1931, was a Shanghai writer and literary critic. He became a favorite of Madame Jiang, a former Shanghai actress who in the 1960's gained enormous power in the Communist Party, particularly over cultural affairs, as Mao grew increasingly frail.

Madame Jiang sought to radicalize the arts with revolutionary plays and dramas, and unleashed lethal attacks on the Old Guard and those who published what she deemed antirevolutionary or ideologically incorrect works.

At the time, Mr. Yao was living in Shanghai as a member of a group that called itself the Proletarian Writers for Purity. In November 1965, he wrote a blistering attack on a play by Wu Han, ''The Dismissal of Hai Rui From Office,'' calling it antirevolutionary and contrary to Mao's thinking and principles.

The essay, later published in Beijing, is considered the first shot in the Cultural Revolution, touching off debate in political and artistic circles over who followed Mao and who opposed him. A power struggle erupted that shook the foundations of China's leadership and created an era of paranoia and madness in China's biggest cities.

By the late 1960's, Mr. Yao had become a member of the increasingly powerful Gang of Four. Madame Jiang was considered the ringleader, Mr. Zhang was the powerful Shanghai propaganda official who later became a Politburo member and was considered a possible successor to Mao, and Mr. Wang was a labor activist who was also elevated to the Politburo.

During Mr. Yao's trial, the government said he once published an essay that read: ''Why can't we shoot a few counterrevolutionary elements? After all, dictatorship is not like embroidering flowers.''

Photo: Yao Wenyuan, on trial in 1980. (Photo by Tang Likui/New China News Agency, via Associated Press)