On its 30th birthday, the People's Republic of China finds itself recovering from a misspent youth of wild experimentation and political turmoil that have left economic weaknesses and cynicism that may take years to overcome.

The communist government that officially reunified the world's most populous nation on Oct. 1, 1949, has won international accaim for managing fairly well to feed, house and educate nearly a quarter of humanity. But now, with its sights clearly set on becoming a modern world power, China has discovered that this is no longer enough.

At a huge anniversary gathering today in the Great Hall of the People, National People's Congress Chairman Ye Jianying made an extraordinary public confession of the Chinese leadership's past mistakes in letting ideological campaigns get out of hand. He suggested, however, that the torment had made nearly a billion Chinese "more mature politically."

The speech highlighted the conflict in China of great expectations and uncertain prospects. To symbolize the world's stake in this conflict, Chinese Communist Party Chairman Hua Guofeng is preparing to begin a tour of Western Europe -- and next year, the United States.

In the meantime, Peking has canceled traditional National Day fireworks displays as too expensive for a nation with a sick economy. But the Chinese official press has been celebrating the anniversary with reams of figures showing great improvement since 1949, when the late chairman Mao's armies pushed the last Nationalist Chinese forces off the mainland to an island refuge on Taiwan.

The newspaper figures ignore -- although officials here readily acknowledge -- one dark statistic that clouds all other signs of progress: China's population since 1949 has grown by more than 400 million.

"I think that when people compare conditions to 31 years ago, or 35, it's a tremendous change," said one Peking resident who was in China at its low point immediately after World War II. "But if they compare it to just 20 years ago, the change has not been nearly enough."

If there is any area in which the Chinese can claim progress in the last 30 years, it is foreign relations. Through energetic and flexible diplomacy, particularly in the last decade, Peking has regained, and in certain respects enhanced, the world prominence and influence it enjoyed in World War II.

In large part, that prominence grows from good relations with Washington, but China today has equally important trade and diplmatic relations with Japan and Western Europe. This can only enhance its ability to act on the world stage in the 1980s, if its nagging economic problems can be overcome.

The New China News Agency reported this week, for example, that grain production had climbed from 163.9 million tons in 1952 to 304.75 million tons last year and cotton from 1.3 million tons in 1952 to 2.2 million last year. Ye bragged about these figures in today's speech, but taking China's estimated 1952 population of 567 million and 958 million last year, grain has just barely kept pace with population growth and the amount of cotton per person declined slightly.

China has only 5 percent of the world's arable land to feed its huge population. Strained resources and bad weather in recent years had made it difficult to increase crop yield.

Even the announced agricultural growth rates are not very high," said one diplomat here. "They are not even talking about getting a farm surplus, which was the basis for the industrialization of the great Western powers."

"We're not really sure now we can make it," said a 28-year-old Chinese who has spent his whole life under this government. "People need more confidence that the leaders can rid us of the bureaucracy and corruption that affect us."

From 1949 until 1957, China's economy recovered steadily from the war-years and seemed destined for spectacular results. But in 1957 Mao jailed thousands of technicians and intellectuals who had criticized the Communist Party during the "100 Flowers" liberalization campaign. He experimented with a sudden acceleration in economic goals, the Great Leap Forward, that exhausted the population.

After a brief recovery in the early 1960s, Mao began another period of purging veteran officials and technorats from leading positions during the Cultural Revolution. Hard work in many cases was critized as "economism" or "careerism," and the economy suffered.

Memories of those years seemed to permeate the main auditorium of the great hall today as Ye, speaking to an audience of 10,000, including foreign diplomats and journalists, summed up the last 30 years in a two- hour speech. Ye is 81, part of a gerontocracy running China, and he had enough strength to read only the beginning and end of the speech, letting popular radio announcer Xia Qing read the rest.

Last night the fourth plenum of the 11th Central Committee announced that 12 veteran officials, all victims of past purges, had been readmitted to the Central Committee, and Ye's speech went further than any before at his level in criticizing party actions in those years.

From 1957 to 1959, he said, "we had became imprudent. . .arbitrary. . . boastful." During the Cultural Revolution, he said, "no accurate definition was given to revisionism, and an erroneous policy and method of struggle were adopted. . ."

Ye did not criticize Mao for the excesses, however. China's leaders still feel that Mao's name and face, found in nearly every Chinese home, are too sancrosanct to attack directly. Later in the speech, Ye simply warned against giving too much power to one man.

After Mao's death in 1976, his chosen successor, Hua, cooperated with a group of old Mao adversaries, led by Vice Premier Deng Ziaoping, to return the economy to the steady growth and technical expertise of the early 1950s. But they have had difficulty rekindling the popular enthusiasm for the Communist Party and its programs.

"There is still a strong strain of doubt and cynicism among people," said a European scholar with unusually close contacts with the Chinese. "They keep their eye on self-advancement. Politics is too dangerous. They just look out for number one."

"They work hard. They have very clear ideas of what they want to do. But the revolutionary elan is gone. They do the absolute minimum in politics so as to be regarded as trustworthy, but as revolutionary successors they aren't very trustworthy at all."

The current leaders, although many are in their seventies and still absolutely committed to the communist ideals of their youth, appear to sense this malaise. They have tried to do everything possible to reassure people that the tumult of the 100 Flowers campaign and the Cultural Revolution will not return.

Vice Premier Gu Mu, a tidy-looking technocrat with a crew cut, told a group of foreign and Chinese journalists this week that "no possibility exists" of a "strong assertion of political ideology," an extraordinary admission for an official of a Marxist state.

"The broad masses of the Chinese people," he said, "are for stability and against turbulence."

Wrapped around the future of China's economy is the potentially explosive question of democracy and human rights. During the last 30 years, periods of moderate and stable economic growth have accompanied attempts to tolerate some public criticism of government policy and protect people from criminal penalties for speaking freely. Such efforts appear only to interest the thin layer of high school and college graduates who live in the cities. These "intellectuals" no longer grow long fingernails and disdain all physical labor. Many of them work on assembly lines. But people with educations beyond the six or seven years attained by most of China's 800 million peasants still have a special place in the society.

The official press publishes open debates on such party policies as guaranteed incomes for workers. A few young people organize occasional rallies or put up wallposters that directly attack high officials.

The Cultural Revolution closed the universities for several years and demolished the education of the generation now reaching 30 by forbidding free give-and-take in class or outside. The older generation of scientists and technicians now demand a freer atmosphere.

"The party has to have the intellectual leadership of the country on board, so they eased up," said one diplomat. "But they all remember the 100 Flowers, and what happened after that period of relaxation."

Chinese protest demonstrations and wallposters today strike a Western ear and eye as strangely mild. The harshest critiques of government inefficiency or malevolence end with cries of priase for Chairman Hua, the Central Committee and the Communist Party.This reflects in part the Chinese urge to soften all confrontation and the long memories of what happened to intellectuals in 1957 who took seriously Mao's invitation to criticize the party directly.

A few young people -- perhaps no more than 20 -- were arrested earlier this year when they suggested in wallposters that the party was no longer a useful institution. They remain in detention, their fates undecided, but a few articles in the recent official press have raised hopes of their release.

After so many years of convulsive, harmful shifts in power at the top of the party, the aged men who run China seem determined to move carefully. The Central Committee meeting completed this week promoted still more elderly allies of Deng Ziaoping, but left his few remaining adversaries in place on the ruling Politburo.

It is like the strategies of the ancient Chinese game of surrounding your opponent and then just leaving him there.

A drawback of this approach is that it does not deal with China's ancient savior and curse: its huge, entrenched bureaucracy. The Chinese have managed to keep their country together longer than any other through skilled use of government, but they also have learned to obstruct any new initiatives.

China's feeble effort in the late 19th century to follow the Japanese example and modernize under the emperior collapsed because of bureaucratic and palace intrigue. Now Communist Party journals and Ye in his speech today, complain of officials "whose minds are ossified."

Middle-level officials in particular have been unwilling to push such new policies or bonuses for good workers because they are afraid that another power shift at the top might change this policy.

After 30 years, those leaders who have, with some interruptions, commanded the Chinese government, do not have much more time to prepare their subordinates for the difficulties ahead. Ye's speech today betrayed for perhaps the first time a note of worry about this.

Most of the 12 men added to the Central Committee yesterday are in their seventies. Today when the Central Committee members on stage had to stand, about a dozen white-coated attendants rushed over to help the most feeble members.

"Old cadres are long tested and well experienced. . ," Ye said. "But it must be admitted that they are advanced in age and that their strength is failing. Middle-aged and young cadres are too few in number in the existing leading bodies."

The next generation of leaders, men in their sixties and late fifties, are not well-known and their intentions are unclear. They lack some of the old relationships enjoyed by the revolutionary veterans that have helped mend serious tears in the political fabric in the past.

One diplomat here who has studied some of the new men said, "If the current leadership could stay in power, I think they could see this through without trouble, but the younger men may be more liberal, and push change faster than Deng and the others. And if they do that, there may be a reaction, which could bring us back to the Cultural Revolution."