With the nation's economy badly sagging and its population showing alarming signs of restiveness, China's top leaders have shelved most of the liberal reforms they introduced two years ago and tightened controls over political and cultural life.

After a brief fling with freer markets and freer thinking, Communist Party officials have returned to a more doctrinaire policy, issuing strict guidelines for the nation's artists, threatening to crush antigovernment demonstrations, rescinding decision-making powers that had been given to certain industries and requiring party members to attend weekly political study sessions in government offices and state factories.

The forceful reassertion of central party control coincides with the recent adoption of a new austerity drive aimed at wiping out China's double-digit inflation and $7.4 billion budgetary deficit -- at the expense of cutting 10 million jobs a year and slashing the production of consumer goods.

Diplomatic analysts believe officials have moved to a more strident tone to prepare the Chinese people for harder times and to head off the kind of demonstrations by workers, students and unemployed job-seekers that took place in several Chinese cities last year.

The crackdown also is seen as an outgrowth of intense political infighting at the party's highest level, where the dominant faction headed by Vice Chairman Deng Xiaoping is trying to edge out Chairman Hua Guofeng and to replace him with a Deng ally before the next party congress.

Deng, according to some diplomatic sources, has been trying to appease Hua's conservative backers in the ruling Politburo by dropping the liberal reform package he fashioned two years ago. The program extended financial autonomy to thousands of industrial managers, offered material incentives to Chinese workers and loosened controls on art, films, literature and party criticism.

Deng gave the first signal of a clampdown when he delivered a get-tough speech at a high-level party work conference in mid-December. In the speech, parts of which later appeared in a Shanghai newspaper, he attacked so-called rightists who have taken advantage of the greater leniency by opposing the party.

"Some counterrevolutionary elements are flagrantly engineering explosions and distributing counterrevolutionary leaflets to oppose people's democratic dictatorship," said the article in Liberation Daily. "In some places people are setting up illegal organizations, publishing illegal journals, spreading antiparty and antisocialist sentiments and even establishing secret ties with one another.

"In some democratic elections at the grass-roots level, some people, in the name of campaigning for official posts, are wantonly making reactionary remarks to attack the party leadership and socialist system."

Deng's speech, according to official Chinese sources, reflects deep concerns among senior party leaders about the spurt in antigovernment protests, civil disobedience, formation of non-Marxist groups and organizations of independent labor unions in Chinese factories.

Among the most disquieting developments have been efforts by disgruntled workers in the industrial cities of Shanghai and Wuhan to set up Polish-style labor associations free of Communist Party controls. Some of these worker groups had printed pamphlets and elected officers before factory bosses ordered them disbanded, sources said.

Senior party theoreticians are known to be closely watching the Polish labor crisis, viewing it as a possible precendent for China. Some have said privately that the next year will be a crucial period for the Chinese party to repair its badly damaged prestige among workers and intellectuals.

Other signs of social and political unrest among normally docile Chinese are said to have alarmed party leaders. In Canton, several young soldiers were disciplined for wearing bell-bottom trousers on weekends and singing Taiwan and Hong Kong love ballads' during their work breaks, according to a Chinese official.

Early this year, three bombs were exploded at different times at the same power plant in Shanghai, Shanghai sources reported.

In the northern city of Taiyuan, three workers recently were jailed for forming a Chinese "Democratic Party" with its own flag, emblem and manifesto.

During the nation's first local election last fall, a handful of college students ran on non-Marxist platforms, incurring the wrath of some school officials. When college officials tried to stop the campaign of one non-Marxist in Hunan Province, 4,000 students staged a sit-down and 87 went on a hunger strike for four days.

In an effort to counter what appear to be small and unrelated acts of dissidence, China's officials have fashioned a medley of harsh warnings against "counterrevolutionary behavior" and campaigns calling on the people to emulate past revolutionary heroes and develop "socialist spiritual civilization."

In the process, the party once again has clamped down on the nation's beleaguered artists and intellectuals, who have enjoyed relative freedom in recent years.

Last month, however, a new set of guidelines was distributed in a Central Committee directive, known as Document No. 7, which ordered that writers and artists "exert themselves to depict the great deeds of the party and the people in socialist modernization," according to sources familiar with the order.

Most controversial since the crackdown has been the government decision to ban a film, titled "Sun and Man," which portrays the life of a Chinese artist who suffers badly during the Cultural Revolution despite a lifetime of patriotism.

Officials cited dozens of "offensive" portions of the film, sources said, but concentrated their attack on the movie's name and scenes of Buddha worship, which they thought could be construed as an attack on the late chairman Mao Tse-tung. The dramatic high point of the film comes when the hero pleads with his daughter not to leave China. In an emotional scene, he explains to her how much he loves China and would never leave.

"But does the motherland love you?" replies his daughter, stunning the artist.

Ordered to make numerous changes, the director and crew have returnd to the film studio to make "Sun and Man" conform to the new guidelines.