THE Communist Party plans to goad many of China's 800 million farmers into collective labor and alter the private tilling that has lifted the countryside to unprecedented prosperity.The apparent retreat in rural reform was outlined Friday in a communique at the conclusion of a full meeting by the party's Central Committee. The measure rolls back China's most beneficial market-oriented reform, in which rural families have leased land formerly under communal control. Under the privately run farms last decade, grain production jumped by more than one-third and the income of the average farmer tripled. Paradoxically, as the party endorsed the setback for private farming, it affirmed the policy of market-oriented economic reform initiated by senior leader Deng Xiaoping in 1978. This contradiction highlights the continued factional rivalry between reformers and conservatives within the party leadership, Chinese officials said on condition of anonymity. Some farmers fear leftist leaders might use the new rural policy to revive the centralized farming that locked rural China in poverty for decades before Mr. Deng's reforms, Chinese officials say. Proponents of the policy say it will enable China to grow more grain with fewer hands and halt a recent decline in per capita grain supply. China must raise yields by 18 percent in order to reach the target of 880 pounds in per capita grain production by the next century. Advocates of the plan say China is unlikely to enjoy further gains in grain productivity from its millions of small, family-contracted plots. China must combine small family farms and enlist redundant farmers in collective endeavors such as repairing irrigation works and providing basic agricultural services, they say. The party vowed "to energetically develop the rural socialized service system and gradually strengthen the collective sector of the rural economy," according to the New China News Agency. The party acknowledged that the system of family-run farms, or the "household-based contract system," is "welcomed by the masses very much." But the communique spoke only of "stabilizing" the system as part of an effort to "deepen the rural reforms." Conservative leaders have often used such euphemistic jargon when halting market-oriented reform. For more than a year, China has implemented in a handful of provinces a "dual-management system" in which peasants were encouraged to surrender their contracted land to either collective managers or an especially talented, nearby farmer. The idle farmers have found work in rural factories or in collective enterprises that offer the enlarged farms basic supplies, marketing, irrigation maintenance, and other services. The scheme is aimed at integrating "the superiority of collective management with the enthusiasm of peasant household production and management," state councilor Song Jian says. After the nationwide crackdown on pro-democracy activists in June 1989, some cadres said the family-based farming system had nurtured capitalism, says Zhang Guangyou, editor in chief at the official newspaper Farmer's Daily. Regardless of the aims of Beijing, ultra-leftist or power-hungry leaders at lower levels might use the party's vague emphasis on collective management to justify a sweeping recentralization of farming, Chinese officials say. "Although the household contractual responsibility system has achieved marked economic gains, there are always cadres - especially at the grass roots - who confuse it with the 'capitalist road said a recent Farmer's Daily commentary. The cadres "tend to look at the dual-management system as unified and collective farming only." Despite the new emphasis on rural collectives, the party strongly affirmed that its main mission is to promote China's economic development. "What is most important ... is to carry out in a comprehensive manner the party's basic line of taking economic construction as the focus ... and persisting in reform and opening to the outside world," according to the communique. The statement indicates that Deng has managed to hold together the shaky consensus behind his apparent belief that, for now, achieving prosperity is at least as important as Marxist purity, the Chinese officials say.