Peking's leaders have told the Chinese people that they must make an unprecedented shift from mass political campaigns to working to build up the economy because of the threat of an attack from the Soviet Union.

An authoritative editorial published Monday in the People's Daily and reaching here today said the "major problem that we must contemplate" is "how much time will the international situation allow us for the four modernizations,"-of agriculture, industry, national defense and science and technology.

The Communist Party Central Committee and its leaders Friday concluded a series of landmark meetings held in Peking over the past several weeks. They announced that the domestic political campaign against the disgraced, dogmatic "Gang of Four" including Chairman Mao's widow, Chiang Ching, was being would up so that all available time could be devoted to building the economy.

The People's Daily editorial provided the most specific explanation so far for the sudden policy shift, which seems to curtail a system of government by mass political campaign that the Chinese have been using for at least 20 years.

In mentioning the threat of an attack by the Soviets, the editorial gave no hint of any recent Soviet actions that would heighten concern about an attack, but the sudden Peking decision to normalize relations with Washington also seemed to reflect great worry about Moscow's intentions.

"If we do not shift the focus of our work, make a big push in the modernization drive, strengthen our country and improve the people's living standards, the dictatorship of the proletariat in our country cannot possibly be consolidated and we would be at the receiving end when a new war of aggression breaks out," the editorial said.

"Modernization will be the central task for the whole party from now on, so long as there is not a large-scale enemy invasion," it said. "All other work, including the party's political work, will focus on and serve this central task.

"There must be no 'political movement' or 'class struggle' which deviates from this central task and damages modernization."

Although it has warned for years that the Soviet Union eventually would start a major war, Peking has usually predicted that the Soviet attack would foucus on Europe and bring a major confrontation with the United States rather than with China.

But peking has seemed concerned, by recent reports of attempts by the Soviet Union to get its Eastern European client states to contribute more to Soviet bloc forces in the West so it can beef up its army on China's border.

The Chinese also have complained bitterly of Moscow's new friendship treaty with Vietnam and says there are signs of increased Vietnamese military preparations near China's southern border. The People's Daily yesterday recounted several recent alleged Vietnamese border incursions it said had caused the deaths of several Chinese, and issued a blunt warning.

"China has never bullied and will never bully any other country," the party newspaper said. "Neither will it allow itself to be bullied by others. It will not attack unless it is attacked. But if it is attacked, it will certainly counterattack.

. . We state this here and now. Don't complain later that we've not given you a clear warning in advance."

The People's Daily also repeated the pro-democracy appeal contained in the communique of the 3rd plenary session of the 11th Central Committee released Saturday. It indicated that some party leaders had complained during the high-level Pekng meetings about the continuing wall poster campaign criticizing officials in China. "Some comrades, when they see people putting up wall posters, raising opinions about the leadership, or seeing that some of the posters raise improper questions, dismiss these methods as detrimental to stability and unity. This is entirely wrong," the editorial said, according to a summary released here by the official New China News Agency.

"Putting up big-character posters is the democratic right of the people guaranteed by the constitution and this right cannot be suppressed."

The agency also reported memorial services held for two deceased Chinese leaders-former defense minister Peng Teh-huai and the party's former number four leader, Tao Chu-after the official rehabilitation of their reputations by the plenary session.

The eulogy for Peng by party vice-chairman Teng Hsiao-ping was remarkable in that it made no reference to Peng's outspoken criticism of Chairman Mao Tse-tung's disastrous effort to build the economy through rapid collectivization in the late 1950s. Peng was purged because of his opposition to Mao, and the agency's report was the first official confirmation that Peng died nov. 29, 1974.

The plenary session also provisionally added nine new members to the Central Committee, nearly all of them political allies of Teng, now the most influential man in the Chinese leadership.

Many of the new members, such as Army Gen. Chen Tsai-tao and veteran bureaucrat Sung Jen-chung, were purged by Mao during the Cultural Revolution of the 1960s for opposing his effort to destroy what he felt was a new bureaucratic elite in the country.

The other new Central Committee members include several recent appointees to top provincial and central posts, such as Huang Ke-cheng, Hu Chiao-mu, Hsi Chung-hsun, Huang Huo-ching, Han Kuang, Chou Hui and Wang Jen-chung.

The New China News Agency also announced today the appointment of new Central Committee member Wang, the party chief in Shensi Province, as vice premier. The appointment was made today by the standing committee of China's rubber-stamp parliament, the National People's Congress.

The editorial and other materials released by the official New Chinese News Agency today appeared to follow generally the new rule that all leaders should be referred to as simply "comrade," to eliminate bureaucratic pride and personality cults. Occasional references to "Chairman Hua" and "Vice Chairman Teng" still appeared, however.

Despite the dismantling of many of Mao's policies, China still celebrated the late chairman's birthday today with several press articles, including a 1958 Mao statement, that seem to support the new shift from politics to science and modernization.