Chinese authorities, aided by student supporters, have cracked down on an outburst of free expression at China's leading university, tearing down or covering up wall posters that criticized Japan and called for liberty and democracy.

Amid about 200 to 250 posters pasted on bulletin boards at Peking University last month to protest Japanese "militarism" and trade policies were a few that directly criticized the ruling Chinese Communist Party.

Put up by an undetermined number of students, the posters stirred considerable interest among other students. But they were visible for little more than a week before they began to be torn down or covered over.

Small and fleeting as it might have been, this rare outburst of free expression seems to have made university authorities and high-level Communist Party officials nervous.

The authorities, aided by university professors, have warned students against taking part in unauthorized demonstrations or listening to a "small minority of bad people" who might take advantage of the situation.

By Oct. 1, the country's national day, Peking University's walls finally were cleared of posters registering protest against the Japanese or disagreement with the government or Communist Party.

Much of what happened on the Peking University campus last month was sanctioned by the government, including an officially sponsored campus demonstration against the Japanese. But when some students decided to march off the campus, the gates were closed and police surrounded the university, located in the northwestern section of the Chinese capital.

A march by hundreds of students to Tiananmen Square in the center of the city to commemorate the 54th anniversary of Japan's invasion of China on Sept. 18, 1931, appears to have been made in defiance of official guidance. But under the watchful eyes of the police, the students remained orderly.

Given the extensiveness of police control here, the spontaneity of some of these events impressed some diplomats, one of whom said they reflected "a degree of ferment" among university students.

Last week, students also staged an anti-Japanese protest in the central China city of Xian, Reuter reported. Foreign witnesses said thousands of students had protested Japanese Prime Minister Yasuhiro Nakasone's attitude to his country's wartime past and against what they called the dumping of inferior Japanese goods on the Chinese market. But a Xian foreign affairs official said only 100 to 200 students staged the protest and said it was not organized by "official organs."

The posters at Peking University generated great interest on the campus. For several days, students could be seen studying the posters, taking notes and even looking at them by flashlight at night. Outside the campus, there appeared to be little interest or even awareness of what was going on. But university security forces were confiscating film taken by foreign journalists, apparently out of concern about how the student protests might be reported abroad.

Some of the students appeared to be angry about the presence of the police around the campus. One poster, entitled "Blood, Blood, Blood," complained about the police and the Japanese consumer items, such as refrigerators, that have flooded the country. The Chinese press has reported several examples of inferior goods being sold to meet China's booming appetite for consumer items.

"What has all our sacrificed blood given us?" the poster asked, in an apparent reference to the Japanese occupation of China. "Police and refrigerators."

Most of the posters conveyed protests against the Japanese. Some, such as one that urged readers to "submit to the Party's leadership," supported the Chinese Communist Party and its policies. But scrawled under that poster was the comment that the Communist Party is "not perfect" and "not the embodiment of wisdom."

Another poster said that "veiled threats" concerning students' future job assignments, which are made by the state, had been made to deter students from demonstrating. While supporting the Communist Party's efforts toward economic reforms, another poster said "the modernization of the country is not only a matter of economic modernization but also one of modernizing the thinking and ideology of the nation."

Another poster, dated Sept. 20, said that "in the battle between democracy and dictatorship at Peking University, dictatorship has won. But this is not yet the end. It is now time to hold a burial service for dictatorship."

"There should be democracy, law and genuine freedom!" another poster said.