BEIJING, Dec 13 (Reuter) - China's Wei Jingsheng, imprisoned for much of his adult life, spent his youth as one of Chairman Mao Tsetung's ultraleftist Red Guards before turning on the Communist Party and calling for Western-style democracy.

Even before being sentenced Wednesday to 14 years in prison after being convicted of conspiring to subvert the government, Wei already was among China's longest serving and best known political prisoners.

First jailed in 1979 for "counter-revolutionary incitement," convicted of advocating democratic change and passing military secrets to a foreign reporter, Wei served all but the last six months of a 15-year jail term.

Like his original conviction, his parole in September 1993 was widely interpreted as political -- timed by the Chinese government to improve its image in its drive to bring the 2000 Summer Olympics for Beijing. The Olympic bid failed.

Six months later, in April 1994, Wei was taken from his home after meeting a senior U.S. human rights official and vanished into China's shadowy gulag. His girlfriend, Tong Yi, was arrested four days later and has been imprisoned.

China did not formally charge Wei until last month.

Wei's long years in China's prison took him to labor camps in western Qinghai and a salt farm not far from Beijing. He lost most of his teeth due to poor prison food and lack of exercise.

Born in Beijing in 1949, the year the communists took power, Wei graduated from middle school and answered Mao Tsetung's call to attack "bourgeois bureaucrats," becoming one of the marauding Red Guards who terrorised China during the radical 1966-76 Cultural Revolution.

In 1968, he joined thousands of radical youths in going to the countryside and in 1969 joined the People's Liberation Army.

In 1973, he was demobilised and worked as an electrician in Beijing's parks, including a stint at the Beijing Zoo.

But in December 1978 he became involved in the so-called Democracy Wall in central Beijing, where people posted protest messages in an outpouring of opinion and dissent after decades of repression.

He helped to publish a magazine called Explorations that first appeared in late 1978 and advocated what he called the fifth modernisation --democracy -- a wry twist on the Four Modernisations espoused by paramount leader Deng Xiaoping.

He was arrested in March 1979 and sentenced that October for "counter-revolution" and leaking secrets about the Sino-Vietnam war to a foreign reporter.

Human Rights Watch/Asia said the military secrets Wei was accused of selling were information that had already been broadcast on Chinese television about China's February, 1979, invasion of Vietnam.

In December 1978, his article the "Fifth Modernization" had been pasted in its entirety on Democracy Wall. In March 1979, he and other Democracy Wall writers were denounced by Deng, architect of China's economic reforms.

Wei responded by writing and circulating an article, "Democracy or New Autocracy?," in which he said Deng was becoming a dictator like Mao Tsetung.

The article is believed to have incurred Deng's personal anger and contributed to the severity of his sentence.

In his article on the fifth modernisation, he argued that the Communist Party had deceived the Chinese people, promising them control over their own destiny to achieve its victory over the Nationalist goverment, but then imposing its own rule.

In one article, he described party rule as "feudal socialism" or "feudal monarchy disguised as socialism."

"The people must have the power to replace their representatives at any time so that these representatives cannot go on deceiving others in the name of the people," he wrote.

The ruling party argues that Western-style democracy is unsuitable for China because of its history, low educational level and vast size, which require a more authoritarian form of government to develop the economy and prevent chaos.

During his six months of freedom, Wei frequently and openly attacked the government and said he had no regrets about taking a public stand.

Wei was once engaged to be married to a Tibetan woman whose father was jailed for 18 years after China's early crackdown in the 1950s in the Himalayan region.