The largest petrochemical complex in the Balkans now feels like a post-industrial ghost town, scarred by hellish fires and choked with twisted debris. No one works here, except the U.N. inspectors who arrived today, and they are very careful where they step.

Just as the scorched and looted landscape of Kosovo is a legacy of the late war, so too are the oil refinery, fertilizer plant and petrochemical complex of Pancevo, which were heavily and repeatedly bombed by NATO warplanes.

From their ruptured storage tanks, they bleed a toxic witch's brew of ammonia, crude oil, liquid chlorine, hydrochloric acid, mercury and vinyl chloride monomers--a component of industrial plastics.

The chemicals, some of them highly carcinogenic, burned out of control for days, drifting through the city of 130,000 in clouds of white mist and black smoke, spreading across the landscape and drooling into the canals and rivers that feed the Danube River. Officials reported "black rain" falling in nearby regions.

Teams of technicians and inspectors from the U.N. environmental agency and from FOCUS, a similar group composed of Swiss, Russian, Austrian and Greek members, entered the complex today to scratch in the dirt and dip vials into canals to see what the NATO bombardment wrought. The samples are being sent to laboratories around the world, and recommendations and reports will be issued soon.

Roland Wiederkehr, a member of the Swiss parliament and of FOCUS, said he saw droplets of mercury spattered around the site, while the transport canals beside one of the plants were filled with crude oil. "It was just amazing to see," Wiederkehr said.

The environmental damage at the site will take months, and perhaps years, to assess--along with its potential threat to human health. Moreover, it will be difficult to determine specific effects of the bombings here, since Pancevo has had problems with lower-level pollution for years.

The city itself--about 10 miles from Belgrade on the north side of the Danube--was spared a good measure of the airborne fallout from the airstrikes, because prevailing winds blew most of the smoke to the west.

But in the days after the initial bombings, government officials suggested that pregnant women leave the city, and some physicians have since suggested that women early in their pregnancies seek abortions.

Before dawn on April 18, NATO bombs hit a storage tank containing vinyl chloride monomers (VCM)--a notorious carcinogen--which burned and produced a white fog that spread across Pancevo.

Around sunrise, the Pancevo Institute for Health Protection recorded concentrations of VCM moving through the town that were 10,600 times more than safe industrial levels.

Pancevo Mayor Srdjan Mikovic recalled how the cloud rolled across the city and how people ran into the streets, some wearing masks, to watch it pass. Mikovic said it seemed like something out of a horror movie. "We made a videotape," he said. "You can see the gas floating through our town."

On June 5, Mikovic sent an urgent appeal to humanitarian and environmental groups around the world, warning them of the cost of bombing the city's petrochemical plants. "Pancevo has become a ghost city covered with black clouds on the sky and mixed poisons, which rolled through the streets trying to find its victims," he wrote in an e-mail that day. "The surroundings of Pancevo turned into a huge refugee camp"--a reference to the tens of thousands of people who fled the city because of the smoke.

Mikovic appealed to NATO to stop bombing the chemical facilities. "I am sorry that when I began to warn authorities here and in Europe how dangerous it was to bomb Pancevo that nobody paid any attention," he said.

At his office today, Mikovic offered his guests postcards of Pancevo that showed burning refineries and black smoke floating over the city. "I am sorry I cannot be more merry," he said. "But look at these."

During the war, NATO spokesmen described the plants as legitimate military targets, and few allied officials seemed to consider the possible environmental hazards of bombing the petrochemical and fertilizer facilities.

The complex was built in consultation with engineers from the United States and Europe, and Mikovic said NATO airstrike planners should have known what was in the storage tanks.

Simon Bancov, Belgrade's inspector for the protection of the human environment, has warned against eating vegetables produced in the immediate area of Pancevo. He also has issued a temporary ban on fishing in the nearby Danube because of the potentially large quantities of toxic chemicals that continue to seep into the river--already one of the most polluted in Europe.

Mikovic said he does not want to sound too sensational about the environmental and health impacts of the bombing. He welcomed the U.N. and FOCUS groups to do their testing and write their reports. "Then the world will know what is the truth," he said.

CAPTION: A member of U.N. investigating team loads his camera to record NATO bomb damage to a railway line at the petrochemical complex in Pancevo, where repeated wartime airstrikes caused extensive and potentially dangerous environmental pollution.