China has set the stage for Sunday's opening of the national parliament with a series of disclosures apparently designed to give the new national government an image of candor and stability.

In the past few days the official press has published an unusually detailed discussion of China's criminal justice system, hinting that it was responding to foreign criticism of Peking's human rights policy. The Chinese have aslo begun to report recent cases of corruption, instead of exposing only wrongdoing that occurred before the dogmatic "Gand of Four" faction was purged in late 1976.

Even act of announcing a week in advance the opening of the Fifth National People's Congress, as the Chinese call their parliament, was a drastic departure from the secretive practices of the past 12 years. After the Cultural Revolution began in 1966, faction squabbles before and during important national conferences became so intense that the meetings were not announced until they had been held.

Veiled attacks on "opportunists" in the Communist Party leadership published in oficial newspapers recently suggest that Peking decision makers stillhave serious problems to workout. The National People's Congress is expected to reveal who is to fill key posts such as premier and minister of defense, thus giving the clearest indication to date of the power structure of post-Mao China.

The larger amounts of information the Chinese have begun to supply now about sensitive topics, however - although still thin in comparison to what Western governments churn out - indicate a new confidence among Chinese leaders. They are not speaking so often in generalities and parables, as they did in the last two years of Chairman Mao Tse-Tung's life, when they geared that domestic polical opponents would use their words against them.

The official News Agency released articles this week delving into treatment of political offenders and convicts at the Peking prison. The prison article revealed for the first time the prcentage of exconvicts who commit new crimes, according to the agency only 12 percent gave to her statics that shed a little light on a very dark corner of Chinese society.

The Chinese illustrated their new sensitivity to foreign criticism of the criminal justice system with a detailed report of the trial process used in convicting a truck thief. The report appeared, significantly, in the latest edition of China Teconstructs, the glossy monthly published in several languages and distributed abroad.

In a n interview with Prof. Han Yu-tung of the Chinese Academy of Social Sciences law institute, a New China News Agency reporter asked: "What about capital punishment which is widely opposed now abroad?"

Han gave the standard Peking line that only those "who owe blood debts or are guilty of other extremely scrious crimes" should be executed, but the fact that the question was raised in such a way indicates the Chinese have noted criticism of reported executions.

A spokesman for Amnsety International in London said Peking has still not responded to letters appealing for an end to capital punishment.

The New China News Agency also reported that two party officials in a county near Peking had been dismissed after one bribed his daughter's way into a college entrance exam and arranged to get answers to her. The Chinese have rarely reported corruption cases in such detal in the past.

An announcement Thursday of the schdule for the National People's Congress indicated one step in the Chinese system of legal due process - the procuratorship - would be restored in a new constitution to be voted. The schedule said the congress would fill the office of chief procurator head of a national system of prosecutors that was abolished after it was accused of suppressing youth Red Guards during the Cultural Revolution.

"Things are going much better than expected," Party Chairman Hua Kuo-feng was quoted as telling the Communist Party Central Committee this week.

The Central Committee holds such meetings before congress sessions to approve the decisions that the parliament will rubber-stamp. The official Chinese account of the session did not describe the new constitution to be approved nor did it name the new state leaders, saving those announcements for the congress.

It did reveal the new lyrics for the national anthem. "Stand up!" would be approved. Chinese for years have been only able to hum the tune because the lyricist got into political trouble during the Cultral Revolution.