A leading figure in China's tiny democracy movement has been arrested in what is believed to be the beginning of a major government drive to mop up the few dissidents, underground publications and unofficial organizations still remaining from the Peking spring of 1979.

Reliable Chinese sources said Xu Wenli, the editor of a prominent underground journal that ceased publication more than a year ago, was seized at his home April 10 in a midnight visit by agents of China's Public Security Bureau. The agents took his papers and tape recordings but gave no reason for his arrest, sources said. h

One of Xu's colleagues also has been arrested, the sources added, and other unofficial magazine editors who gained prominence during the brief flowering of wallposters and unofficial publications in Peking two years ago fear they too will be detained soon.

The arrests came a few days after the Communist Party in its theoretical journal Red Flag threathened to use the courts against "counterrevolutionaries" who hold secret meetings to exchange their experiences, publish clandestine writings and "conspire to spread chaos."

Following a strident attack against political activists by Vice Chairman Deng Xiaoping in December, the party began circulating a secret document calling on provincial officials to stamp out unofficial publications and organizations, according to well-placed sources. Local officials were told to report on their progress by June 1.

The document orders local authorities to search out such illegal activities, ban them and arrest or question anyone who ignores their instructions, the sources said. Officials found helping to circulate or publish underground materials would be expelled from the party, the document is said to warn.

China's democracy movement, never large or well-organized, has greatly dissipated since the official crackdown on dissent began in October 1979 with the sentencing of Wei Jingsheng, the best known activist, to 15 years in prison for "counterrevolutionary" behavior. Shortly afterward, the government banned wallposters from Democracy Wall, a brick fence in downtown Peking where most of the young dissidents came to sell underground journals and meet with foreign correspondents.

Trying to avoid a confrontation with authorities, most of the underground journals stopped publishing, including Xu Wenli's April 5 Forum, a thin hand-mimeographed magazine containing social commentaries and discussions on democracy. Like most of the unofficial writings, April 5 Forum fell short of criticizing socialism or the Chinese Communist Party.

After silencing his journal, Xu, 37, an affable, balding man who worked during the day as an electrician at the Peking train station, began putting out a "newsletter" distributed through the mail. Xu and other editors claimed the several hundred copies they printed were personal mail whose circulation is guaranteed by the constitution.

Last fall, sorting through the first edition of the "newsletter," piled on the tiny desk that was the base of operations in his one-room apartment, Xu said he would use the mails until the government formally licensed his magazine. But he is said to have abandoned that plan when the party stepped up its attacks against political activists late last year.

Xu emphasized in an interview then that he supported the party and socialism but believed that democratic freedom to elect leaders was necessary to help the nation modernize. Nevertheless, he conceded, most Chinese were more interested in improving their life styles than increasing their democratic rights.

Within Peking's small dissident community, Xu's arrest is seen as the start of a harsh crackdown. Some sources believe the clampdown will reach China's artistic community, which has attracted official scorn in recent weeks for writings and films critical of the party and the late chairman Mao Tse-tung.

Two days ago, the Army's official newspaper printed a front-page editorial calling for a public repudiation of literature and movies that it said damaged the party's image and "viciously marked and negated" Mao.