OVCARA, CROATIA, JAN. 6 -- U.S. Ambassador to the United Nations Madeleine Albright visited the guarded site of a mass grave here today, calling it "a symbol of the inhumanity" that has characterized bloodshed in the Balkans and demanding that it be investigated by a war crimes tribunal.

The fenced site, at a small dump on the Ovcara collective farm, is believed to contain the bodies of 200 Croat hospital patients summarily executed by Serb soldiers in November 1991. It is six miles from Vukovar -- a city that the Serb-dominated Yugoslav army seized by pounding it into rubble.

The area now is under the authority of the breakaway "Krajina Republic," established by Croatia's Serb minority.

Albright used the visit to underline U.S. support for the war crimes tribunal set up last year by the U.N. Security Council. She noted that the Clinton administration is providing $25 million to help fund the 11-judge body and to pay at least 15 U.S. investigators and prosecutors for its staff.

Ovcara has become a test of the tribunal's credibility, as Croatian Serbs have blocked several attempts by international investigators to dig up the bodies for examination.

Russian soldiers from the U.N. peace-keeping force stationed in Croatia now guard the site 24 hours a day to prevent tampering with evidence. American forensic pathologist Clyde Snow discovered the site in October 1992.

"This mass grave is the symbol of the inhumanity that took place, and it is absolutely essential that this particular site be investigated," Albright said. "It is a great tragedy that human beings would end their lives in what is ultimately a garbage dump."

At a news conference in Zagreb, Albright said the United States would insist that the Yugoslav, Croatian and Bosnian governments cooperate fully in the investigation of 98 sites in Bosnia and Croatia, which are suspected of containing 3,000 to 4,000 bodies.

Albright indicated that the U.S. vote on any eventual lifting of economic sanctions on Yugoslavia would be influenced by the attitude of the government of Serbia -- Yugoslavia's dominant republic -- and its Bosnian Serb allies toward the tribunal.

Britain and France reportedly do not share U.S. urgency on the tribunal, arguing that a peace settlement should have top priority and that prosecution of suspected Serb war criminals would impede the process. During the Bush administration, U.S. officials labeled Serbian President Slobodan Milosevic and Bosnian Serb leader Radovan Karadzic "war criminals."

The tribunal held its first session at the Hague in November but has done little since because of a lack of personnel and funds. It has no authority to try suspected war criminals in absentia or to force those it indicts to appear.

The ability of the Serbs to impede the tribunal was made clear before Albright's visit. At first they refused to allow it and then demanded that she meet the Krajina leadership.

There were warnings that local Serbs might block the roads or that her convoy might come under sniper fire. The visit, on the eve of the Orthodox Church's Christmas, took place without incident. Albright agreed to shake hands with the so-called republic's outgoing president, Goran Hadzic, and the leader of the regional council, Milan Ilic, but left the talking to the U.S. ambassador to Croatia, Peter Galbraith.