The head of a U.N. team investigating environmental damage in Yugoslavia said yesterday that the team has found no evidence that NATO bombing caused major ecological catastrophes. But Pekka Haavisto, the former Finnish environment minister who led the team’s 10-day tour of Serbia, called for urgent action to help clean up “hot spots” of war-related pollution. In particular, he asked for steps to prevent more dangerous substances from leaking into the Danube River. Haavisto said it was difficult to distinguish between pre-existing environmental damage in Yugoslavia and damage caused by the war. After more detailed laboratory tests and evaluation, a final report on the investigation will be submitted to U.N. Secretary-General Kofi Annan by early September.