When President Clinton visited Kosovo two weeks ago to speak to a hand-picked audience of parents and schoolchildren, he made a special plea for ethnic tolerance by the province's youths. They should, he said, be spared the burden of their parents' blind ethnic hatred.

But on the streets of Kosovo's major cities, human rights monitors have discovered that children are already caught up in the cycle of enmity. Many of the worst acts of ethnic violence in the Serbian province are being committed by children and teenagers, with the resulting burden of tensions and disorder falling on adults, according to a comprehensive study released here today.

The report by the Organization for Security and Cooperation in Europe cited numerous cases of violence by youths, including 30 grenade attacks on Serbian homes in the city of Lipljan in July and August by a gang of youths between 14 and 20; the stabbing of an elderly Serbian man by a 17-year-old on Sept. 14 in the same city; and the beating of a Serb on the main street of the capital Pristina by five boys aged 10 to 12 on Oct. 26.

"The future of Kosovo lies with its children," said Bernard Kouchner, the top U.N. official in Kosovo, in a statement accompanying the report. "Yet one of the most alarming trends documented in the report is the increasing participation of juveniles in human rights violations. We read . . . of case after case of young people, some only 10 or 12 years old, harassing, beating, and threatening people, especially defenseless elderly victims, solely because of their ethnicity."

The targeting of elderly Serbs by ethnic Albanians is another troubling trend identified by the OSCE, which employed 75 people to collect witness's accounts of human rights abuses since NATO forces entered the province and Yugoslav troops began to withdraw on June 14.

The study represents the most comprehensive survey of the subject to date, and in many cases contains far more detailed and candid accounts of individual incidents of violence than officials of the NATO peacekeeping force in Kosovo have been willing to disclose.

The overall picture provided by the 332-page report is of a territory filled with "lawlessness that has left violence unchecked . . . [in which] impunity has reigned instead of justice." The fault lies with the inability of relevant institutions in Kosovo to follow up reports of human rights abuses with credible investigations that can assign responsibility, the report states.

"For anyone who wants to engage in kidnapping," it says for example, "the chances of detection and arrest are remote."

Great pains were taken by the OSCE--a group of 55 nations, including European countries, the United States, Canada and the former republics of the Soviet Union--to distinguish between postwar human rights abuses in Kosovo and what it described as the more serious, sustained and systematic abuses perpetrated by the Yugoslav government in Kosovo over a long period before the war ended.

The Yugoslav abuses are documented in a separate 433-page report with chapters describing what the OSCE calls the frequent and often arbitrary use of torture, rape, kidnapping, arson, pillaging and other forms of persecution as instruments of Yugoslav government policy. Serbia is the dominant republic of Yugoslavia. Among the frequent victims of this "extreme and appalling" violence were children, young men, women, the wealthy, the elderly and the handicapped, the report states.

"For at least a decade, there was a systematic policy of apartheid . . . for Albanians in Kosovo," Kouchner said. The crimes now being committed by ethnic Albanians against Serbs, he added, "are the acts of individuals." Moreover, the report alleges that Yugoslav government abuses are continuing, noting the reported detention of as many as 5,000 ethnic Albanian residents of Kosovo in unheated and unsanitary prisons in northern Serbia. Most were bused from Kosovo near the end of the war and are facing trials on charges related to the war.

But OSCE officials also found what they called "a disturbing pattern of involvement" in acts of ethnically motivated violence by men dressed in uniforms of the former Kosovo Liberation Army (KLA), known in Albanian as the UCK, who identified themselves as members of the group.

Before the war, the rebel group targeted policemen and other Yugoslav security forces in a guerrilla war meant to secure Kosovo's independence from Yugoslavia; during the war, the rebels staged raids against Yugoslav forces with advice from the West. After the war, the rebel group was officially disbanded, and a substantial portion of its members registered to join a Kosovo national guard.

"The report is littered with witness statements testifying to UCK involvement" in kidnappings, detentions and interrogations after the war, the OSCE said. In some cases, the rebels blamed impostors, but in others, witnesses who knew the assailants testified to involvement by the rebels in kidnappings, illicit tax collection and intimidation or eviction of Serbs and Gypsies in western Kosovo.

The motivation for some of the violence appears to be political. The report "reveals that opposition to the new order, particularly the former UCK's dominance . . . or simply a perceived lack of commitment [by citizens] to the UCK cause, has led to intimidation and harassment," the OSCE said. Officials of the Democratic League of Kosovo, the rebel group's principal political rival, have been kidnapped, murdered, targeted in grenade attacks, accused of disloyalty or told bluntly to withdraw from politics in at least half a dozen cities--in some cases by men who claimed to be members of the rebel group.

The motives behind other violence documented in the report are simply criminal. The robbery of Serbs by armed ethnic Albanians is becoming commonplace, just as it was commonplace for Yugoslav troops to stop and rob ethnic Albanians. But ethnic Albanian shopkeepers and restaurants "appear to be blackmailed on a regular basis," the report states. Ethnic Albanians have also sought to extort ransom fees from relatives of some Serbs who disappeared, even though those kidnapped had already been slain.

Businessmen have been ordered to pay illegal taxes to a provisional ethnic Albanian government led by the KLA, and virtually all of the province's operating factories have been brought under KLA control to ensure jobs and profits for supporters of the provisional government.

But much of the remaining violence has been motivated by revenge for Serbian atrocities during NATO's 11-week campaign of bombing in Yugoslavia last spring, which drove hundreds of thousands of people out of the province.

The report notes that violence motivated by revenge has moved through three phases. During the first stage, violence was mostly directed at suspected participants in atrocities. Next, suspected collaborators, such as gravediggers or those who stayed in Kosovo without being persecuted during the war, were targeted.

Now, virtually all Serbs and ethnic Albanians who stayed behind are likely targets of violence and retribution, due to a widespread presumption of collective guilt. For instance, ethnic Albanians who found their power lines cut and many of their schools destroyed in the war are now denying electric power to Serbian enclaves and blocking access to schooling for Serbian children.

In explaining the involvement of youths in human rights abuses, some schoolteachers and psychologists working in Kosovo have noted that many schoolchildren have reacted to atrocities they witnessed during the war by becoming preternaturally aggressive, a common phenomenon in such instances.

"Many were witnesses as their parents were killed, or they watched other people being killed," the OSCE report states. "It may take years for the children who lived through the conflict to overcome the traumas they have undergone."

One of the more compelling indications of some centralized planning and organization behind at least some of the postwar murders can be found in a shallow grave near the village of Podgradje, near Gnjilane in the sector policed by U.S. troops, the OSCE said.

Fourteen bodies were discovered in or near the grave in July, August and October. All are thought to be Serbs who were kidnapped in small groups from at least three villages and killed elsewhere before being dumped in Podgradje, a scenario that suggests careful planning and considerable freedom of action by a well-organized and centrally directed group, according to OSCE officials.

CAPTION: Targeting of elderly Serbs is a troubling trend identified by the OSCE. It cites, for example, the stabbing of an elderly Serbian man by a 17-year-old.