China's parliament has for the first time written into the country's constitution a commitment to encourage birth control in the world's most populous nation.

A new constitution approved Sunday and published yesterday says that "the state advocates and encourages family planning."

Communist Party Chairman Hua Kuo-Feng, in a speech to the parliament, demanded that China's population growth rate be lowered to "less that 1 percent within three years" - a goal that many Western specialists consider nearly impossible because it would require the number of births annually to be reduced by several million.

Although population has been a traditional problem in China, there had been no mention of birth control in constitutions adopted during the era of Chairman Mao Tse-tung, who sometimes argued that the more workers China had, the better.

Faltering grain production and an estimated population of nearly 900 million people have convinced the post Mao leadership of the need for more careful planning and more modern methods.

Full texts of the new constitution and of parliamentary speeches by Hua and Vice Chairman Yeh Chien-Ying released yesterday reveal deep concern for modernization.

Hua's 3-1/2 hour address to the fifth National People's Congress, the name for China's parliament, gives page after page of detailed development instructions for the next 22 years. The constitution reads as much like an economic action program as it does a statement of political rights and procedures in China.

Many of the provisions in the new document, replacing a 1975 constitution, are throwbacks to a 1954 constitution that reflected the great interest in economic rebuilding after the civil war.

But the article endorsing family planning breaks new ground and is heartily endorsed in the full text of Hua's Feb. 26 speech. He calls birth control "a very significant matter . . . conducive to the planned development of the national economy."

In recent months the Chinese have begun to admit how crucial their birth control program is to plans for increasing individual supplies of food and consumer goods. They claim to have cut the annual population growth rate to under 2 percent in many cities, although many Western specialists think the rate remains higher than that in rural areas.

According to U.N. estimates, China's population growth rate dropped from about 2.3 percent to 1964 to 1.8 percent in 1974. Based on a population of 800 million, each percentage point of growth would equal 8 million persons. But comparison, the 1975 growth rate for the United States was 0.58 percent.

Last fall a Stanford University researcher and a U.S. population team reported that Shanghai, the most populous city in the world, had made its birthrate the world's lowest through widespread monitoring of personal reproductive habits and encouragement of contraception.

Through these programs, the researchers said, Shanghai had achieved a 0.6 percent birthrate, roughly equal to its death rate. In the United States, the average birthrate is now about 1.5 percent.

The new constitution also restores a number of individual rights missing in the barebones 1975 constitution, bringing the total number of articles to 60, compared to 30 in 1975 and 106 in 1954. In language nearly identical to the 1954 constitution the new document strengthens the "right to rest." It says, "To insure that working people enjoy this right, the state prescribes working hours and systems of vacations."

The new document also restores "the freedom to engage in scientific research, literary and artistic creation and other cultural activities. The state encourages and assists the creative endeavors of citizens engaged in science, education, literature, art, journalism, publishing, public health, sports and other cultural work."

A group of dogmatic admirers of Maoist doctrine, including Moa's wife, Chiang Ching, were in charge of cultural work when the 1975 constitution was drafted. They insisted that artists conform to their view of what were proper revolutionary subjects and styles in art. Hua's new administration has endorsed a relaxation in state control over the arts, but made clear that artists must recognize some political bounds, such as avoiding criticism of socialism.

The speech texts showed a strong preference for softening Mao's edicts against material incentives in industry and agriculture. Yeh offered a compromise on the particularly sensitive question of money bonuses: "Those who do outstanding work should be commended and appropriately rewarded in accordance with the policy of combining moral encouragement with material reward, with stress on the former."

The new constitution encourages, as revealed in a summary of Yeh's speech released last week, citizen complaints about inefficiency and arrogance among state officials.Yeh also suggested that China end official state discrimination in job and school placement against the offspring of former landlords, rich peasants and other "bad elements" if they have accepted the socialist system. He advised "prudence" in removing such labels, which are a mainstay of the Chinese Communist system.

The new constitution renewed some legal guarantees, such as secret ballot and right to a defense in court, which have little meaning in a country where prearranged consensus usually decides trials and elections.

The documents also appear to strengthen the chairmanship of the congress' standing committee, making it clear that Yeh, in assuming that title, becomes the ceremonial head of state.

The constitution endorses for the first time, under some conditions, collectivization to the brigade level, a very controversial issue in rural parts of China because it sometimes deprives villages of profitable enterprises.