In a major crackdown on street crime, Chinese authorities are rounding up thousands of mostly young offenders and sending them to remote areas for punishment and labor, according to diplomatic sources.

The sources said a central Communist Party directive handed down in July targeted 50,000 for arrest in a nationwide sweep aimed at restoring law and order in China's cities. The directive reportedly calls on judicial organs to impose the maximum sentence for each crime and to revoke convicts' urban residency permits.

Police dragnets here already are said to have nabbed 3,000 suspects, most in their twenties and thirties, who were charged with crimes including rape, murder, robbery and prostitution.

Working round the clock, police reportedly have arrested suspects at their jobs during the day or at their homes in the middle of the night.

In raids this month in the northeastern city of Tangshan, where nearly a quarter of a million people died in a 1976 earthquake, police arrested 105 reputed gang members accused of armed robberies, murders and assaults, according to published reports.

Courts have sentenced some offenders to prison speedily, but most have been sent to forced-labor camps or special work projects in Qinghai Province, a desolate, poor region of 3.8 million people in China's northwest, and in other isolated areas, according to sources.

The crackdown has prompted an unusual law-and-order publicity campaign here. Signboards have been plastered with photographs of criminals and descriptions of their crimes.

One poster depicts how a 32-year-old man and his girlfriend electrocuted the man's wife. The illustrated story ends with the two culprits in court, their heads bowed, awaiting sentence; the man was executed, and his girlfriend was given a suspended death sentence.

Other signs announced executions of a 36-year-old woman who killed her daughter by locking her in the house and setting it afire; a factory worker, 35, who raped eight women; a 22-year-old thief who strangled his girlfriend with a rope for fear that she would expose him to police; a 30-year-old worker who killed his girlfriend with a meat cleaver after she jilted him, and a 25-year-old burglar who killed a night watchman during a break-in.

Some of the notices were marked by a large red check mark indicating that the sentence had been carried out.

"The government is trying to let people know there are security measures being taken against criminals," said an office worker studying the posters in south Peking. "I hope all the hoodlums get put away."

Sources said the crackdown was ordered by China's top leader, Deng Xiaoping, who believes urban crime undermines public confidence in the party to run China's cities.

Conservatives reportedly have seized on the crime issue as an unfortunate byproduct of Deng's policies of motivating China's labor force by introducing foreign ideas and cutting back ideological controls over the society. Deng's opponents have complained that this is a corrosive influence.

Although China's crime rate is low by western standards--officials say there are 7.5 offenses for every 10,000 people--the number of serious crimes, including rape, murder and robbery, reportedly is on the increase.

Most urban crime is said to be committed by persons less than 25 years old. Many are members of the so-called "lost generation," youths who were incited to rebel during the radical Cultural Revolution from 1966 to 1976, and then were blamed for the chaos.

Unable to find work in a nation whose urban unemployment rate is believed to reach more than 10 percent, these disillusioned youths often turn to crime.

Diplomats said authorities are disturbed by what they view as a breakdown in traditional Chinese social values. Some officials even have expressed fear for their own safety, and guards at residential compounds for leaders reportedly have been put on special alert.

There were official worries that violent crimes might erupt in Peking and draw embarrassing attention to the problem while the national parliament met last June, a source said.

Although crime has plagued the once trouble-free Chinese society at least since the 1960s, only in recent years has the leadership acknowledged the problem publicly and announced measures for dealing with it.

The current crackdown is thought to be the most intense and best coordinated effort to root out urban crime.

Sources said Peking was specifically moved to action by last May's hijacking of a Chinese jetliner to South Korea and by the murder spree of the notorious Wang brothers of northeastern China.

The Wangs, who are said to be in their twenties, are wanted for killing at least 11 police officers and soldiers since February and for robbing an armory of weapons, according to sources. The brothers began their spree in the northeastern industrial town of Shenyang, killing four officers who were interrogating them in connection with another crime.

Armed with pistols, they have moved around the country, killing other officers and soldiers who have tried to arrest them in the northern city of Shijiazhuang and in Wuhan in the south, sources said.

The crimes are regarded as being so serious that the police, for the first time in years, have offered cash rewards for tips or the arrest of the Wangs--$250 for useful information, $500 for information leading to the arrest and $1,000 for actually apprehending the Wangs, according to foreigners who have seen the wanted posters.