The trucks arrived from Kosovo at night, passing beneath a simple concrete arch marking the entrance to a World War II detention camp for German and Croatian soldiers. After threading their way around police barracks and a shooting range, the drivers stopped near the east bank of the Danube River and waited until dawn.

That is when a tractor driver began his work, digging pits roughly 15 feet deep and 30 feet long in the damp clay. The worst moments came next, as the backs of the trucks were opened and the stench of decaying bodies rolled out.

Slain ethnic Albanians from Kosovo were pulled from the trucks and tossed into the pits. Headless bodies. Bits of jewelry and broken watches. Bodies of little boys and girls. Bodies of young and middle-aged women. Identity cards. Cigarette lighters. German currency. A pass to a discotheque. Tennis shoes, socks, shirts and underwear. It all went into the pits, was doused with gasoline and set on fire. When the flames died, the tractor driver switched his engine on and eased a layer of dirt over the blackened sludge.

Those who conceived of the operation expected that these secret horrors would never surface, a reasonable view under the authoritarian government that ran Yugoslavia until last October. What they did not count on was the enduring anger and shame of those who were ordered to drive the trucks, hoist the bodies and operate the tractors.

Finally, two years later, after the downfall of President Slobodan Milosevic and the advent of a government in Belgrade that is willing to listen, these Serbs caught up in wartime horror are beginning to talk. The nightmarish memories they are recounting for authorities form the backdrop for Milosevic's sudden extradition Thursday to a U.N. war crimes tribunal in The Hague and may end up buttressing the charges against him.

The first to speak up was a 56-year-old professional diver, Zivadin Djordjevic, who in April 1999 became embroiled in a police investigation of a truck dumped into the Danube in a remote village east of here. When he opened the back door, he found dozens of bodies. The police initially said they were ethnic Albanian fighters, but women and children were among them.

The investigation was stopped cold by Belgrade that month, but early this year, an account of Djordjevic's experience appeared in an obscure local crime journal, whose editor is a friend of the Serbian interior minister. The government's prompt investigation of the report and its searing admission that the bodies came from Kosovo have opened what promises to be a floodgate of revelations about Serbian wartime atrocities.

In the past two months, according to Serbian police, truck drivers, tractor drivers, ditch diggers, soldiers and policemen have for the first time begun to tell authorities what they know.

Such accounts never circulated in Yugoslavia during the decade in which Milosevic ruled Serbia, but now the news of mass graves near Belgrade containing ethnic Albanians from Kosovo has appeared everywhere in the Yugoslav media. A graphic 15-minute video of forensic pathologists brushing earth from the bodies here at Batajnica, 12 miles northwest of Belgrade, was shown on national television Thursday night, provoking surprise and revulsion.

"Here it was just a whisper," said Petar Knezevic, 32, a Belgrade mechanical engineer, speaking about reports of Serbian war crimes that appeared in Western media during the 1992-95 Bosnian war and the 1998 and 1999 conflict in Kosovo. "They were hiding it because they were afraid they might be prosecuted. . . . Why else would someone go to the trouble of bringing the bodies all the way from Kosovo?"

Thursday evening was when the Serbian government sent Milosevic to The Hague to face charges of responsibility for war crimes in the 1999 Kosovo conflict. The revelations bear signs of an old-style government public relations campaign, aimed at discrediting Milosevic and building support for the Serbian leadership's decision to turn him over to the tribunal.

But the claims are supported by evidence: the exhumations so far of more than 100 bodies in mass graves at two sites, many showing signs of torture and violent death. Police officials say they have collected accounts from witnesses of more than 1,000 bodies being unloaded from trucks at these two sites and heard indirect accounts of additional bodies being buried in bomb craters from NATO airstrikes along the main highway linking the city of Nis with the Kosovo capital of Pristina.

"It's clear that Serbian authorities are publicizing the information . . . in connection with Milosevic. They needed very strong evidence" to help stoke public support for his extradition, said Natasa Kandic, director of the Belgrade-based Humanitarian Law Center. But she said that no matter what the motive, the revelations constitute an important rebuttal of "10 years of denying war crimes were committed by Serbian forces."

At the center of the government's unfolding probe is Dusan Mihajlovic, a businessman and former member of the secret police who was appointed interior minister early this year. "We will try to find the ones who committed the crimes in Kosovo . . . and prove the responsibility of those who made these decisions," he said in an interview. "We are interested in the truth so the families can find out where their loved ones are buried and have them buried properly."

A successful search could help heal an open wound in Kosovo, where more than 10,000 people were killed. International organizations and ethnic Albanian leaders say more than 3,000 ethnic Albanian residents of the Serbian province are missing two years after NATO soldiers occupied the province and Yugoslav forces withdrew. Yugoslav authorities say that more than 1,000 Serbian residents are also still missing.

But the search for mass graves also threatens to touch sensitive power centers in Belgrade, causing Kandic to worry that the government's enthusiasm will flag now that Milosevic is in a jail cell under the tribunal's jurisdiction. Finger-pointing has already begun between the Yugoslav army and the Serbian police, both of which dispatched troops to Kosovo and often conducted joint operations.

The 38 bodies exhumed by police here and the 74 bodies exhumed in a national forest near the town of Petrovo Selo are clearly linked to wartime operations of special police units. Included were at least nine children under age 7 and many women. Identity cards recovered here, for example, list the names of several of the more than 50 residents of the Kosovo town of Suva Reka machine-gunned on March 26, 1999. War crimes investigators say the killings were carried out by policemen angered by the slayings of several colleagues by ethnic Albanian rebels.

Those shot in the attack were tossed by police into a truck covered by a blue tarp; two ethnic Albanian women who had feigned death pulled themselves from the pile of bodies and escaped while the truck was driving away. The driver, an army reservist, later told a Newsday journalist he delivered the bodies to a military parade ground, then picked them up again several days later.

He said he shuttled other bodies between various locations, including several industrial plants where they were evidently burned.

The precise path the bodies took to reach central Serbia is still being stitched together. But many appeared to have been buried at least once before and then dug up, possibly to hide them from war crimes investigators. The base here -- just down the road from a Coca-Cola bottling plant -- was used by special anti-terrorist forces as a training camp. Stanko Grujic, a 75-year-old farmer herding sheep at the edge of the base last week, said that "during the [NATO] bombing, you could not approach it."

Mihajlovic has suggested that army forces also played a role in such atrocities, and he has pointed out that police units were subordinated during the war to army chief of staff Nebojsa Pavkovic, a longtime Milosevic associate who kept the job under the new Yugoslav president, Vojislav Kostunica.

Pavkovic responded last week that "someone is trying . . . to draw the [army] into something it is not involved in."

Since the sniping began, documents that shed light on wartime command responsibilities -- a matter of enormous interest to the U.N. tribunal -- have started to leak from government archives. A classified April 20, 1999, order signed by Pavkovic, for example, put police at the disposal of the general who still commands the 3rd Army; he in turn signed an April 30, 1999, order calling for special units "to clear the field following anti-terrorist operations."

The general, Vladimir Lazarevic, said this referred only to the clearing of "bodies of victims, dead animals, mines and shells." But Mihajlovic and others say it refers to hiding bodies of civilian victims from the war crimes tribunal, an action that one or more witnesses have told them was ordered by Milosevic at a March 1999 meeting at his home.

For now, those who participated at lower levels seem more eager to relieve the burden of the terrible secrets.

A local newspaper printed army psychiatric reports this week, for example, on two young soldiers who told superior officers that they developed sleeping disorders after serving in the Kosovo town of Djakovica. One said he carried "bodies out of a helicopter, bodies of mostly Albanians, massacred bodies," while the other said he repeatedly unloaded bodies from trucks.

More exhumations are slated to be carried out here in coming days under the supervision of a local judge and the deputy head of the Serbian police criminal investigations unit, Dragan Karleusa.

Karleusa said he knows it was wartime and that people were under stress. But he added: "I am ashamed that something like this could happen in Serbia. I condemn this. . . . Only someone with a criminal mind could do this."

He said the system was obviously well organized and that "direct orders were given by high officers." He is still wrestling, he said, with how much responsibility should be born by policemen, drivers and those who loaded trucks.

"What could they do?" Karleusa said. "What is one soldier? Their guilt is incomparable to the ones who organized this."

Special Correspondent Zoran Radjen in Belgrade contributed to this report.Serbian Interior Minister Dusan Mihajlovic, right, and police investigator Dragan Karleusa watch a video of bodies in a mass grave near Belgrade.This mass grave in Petrovo Selo, believed to contain the bodies of dozens of war crimes victims, is one of at least two discovered recently in Serbia.