Its sink or swim for China's party cadres

''Comrade X is absent today. He is studying,'' said the voice over the telephone. Throughout China, callers to factories, schools, or government offices this winter are likely to get similar answers as Communist Party members from top cadres to the lowliest newcomer undergo the process called ''rectification.''

The Chinese leadership stresses that this is not a purge. The Chinese word used, zhengdun or zhengdang, is sometimes translated as ''rectification'' and sometimes as the less meaningful ''consolidation.''

The process will go on for three years, according to a decision of the party's Central Committee announced Oct. 12. At the end of the process, the party's 40 million members, among whom 9 million are counted as cadres (officers), will be required to re-register their membership. Those who, for various reasons, fail to pass the rectification process will not be allowed to register. Those who are found particularly unworthy will be expelled.

The process is not supposed to affect the daily work of the organization concerned, or production in factories. In a number of organizations, it appears to have begun in an experimental way already. Some people who have undergone it say it can be an intense and even harrowing experience. All a person's past merits and demerits are aired, together with the usual demand for self-criticism. Those who have finished the process go around looking as though a burden had dropped from their shoulders, while those who have yet to pass through it are understandably tense and worried.

In the narrow political sense, one purpose of the rectification program is to eliminate stubborn opponents of the Deng Xiaoping line - the policy identified with China's senior leader, which is designed to modernize China by liberal use of economic incentives and other reforms and by opening the country to cooperation with Western countries. The success of China's modernization depends heavily on the willingness of party members to support Deng's policies.

The Deng line, popular with peasants and with citydwellers, has been resisted by conservative bureaucrats and by some Army officers who prefer the rigid centralization of Mao Tse-tung's day.

In a much broader sense, however, the Communist Party of China is itself on trial. The Central Committee's Oct. 12 document minces no words. ''Some party members and cadres have totally forgotten the basic principle of serving the people wholeheartedly,'' it says. ''They ask the party for higher positions and better treatment. They openly violate financial regulations and discipline, sabotage state plans, violate state economic policies, and illegally retain taxes and profits.''

The document gives a detailed catalogue of some of the practices that have most alienated ordinary citizens from party cadres.

''With regard to the distribution of housing,'' it says, ''the increase in wages and many other matters, such as the employment, education, promotion, job assignments, and changing from rural residence registrations to urban residence registration for their children, relatives and friends as well as foreign affairs work, they take advantage of their power and position . . . to seek special privileges, violate the law and discipline, and encroach upon the interests of the state and the masses.

''They ignore the law, protect and shield criminals, and they even take a direct part in unlawful activities, such as smuggling, selling smuggled goods, corruption, accepting bribes, and profiteering.

''Some party cadres in leading positions are seriously affected by bureaucratism. Their revolutionary will has been waning, eating three meals a day yet doing no work. . . . Their serious neglect of duty has caused horrifying waste in the country's production and construction, serious errors in state administration and huge economic and political losses for the party and government.'' The document accuses ''some leading cadres'' of placing themselves above the party organization, and even of turning ''the units under their charge into territories where their will hold sway and where they rule as overlords.''

''These unhealthy tendencies and decadent phenomena, which are seriously sabotaging the nation's socialist modernization,'' the document says, ''have greatly impaired our party's image among the people.''

Deng Xiaoping and another veteran communist leader, Chen Yun, are reported to have made important speeches at the two-day Central Committee plenum which approved the rectification decision.

The texts of the speeches have not yet been released, but Chen Yun, a party elder, stressed: The ''work style of a party in power is a matter of life and death.''