As part of an arms buildup far larger and more dangerous than was known at the time, Iraq embarked on an eight-month crash program to make a nuclear weapon immediately after invading Kuwait in August 1990, the leader of a United Nations inspection team said today.

The Iraqis set themselves a goal of April 1991 to produce a nuclear device. Experts said today that they had no way of knowing how advanced the Iraqi program was when it was interrupted by the Persian Gulf war, or whether the Iraqis could have met their ambitious timetable for constructing a bomb. There is no evidence of foreign complicity in this program, officials said.

The inspection team leader, Rolf Ekeus, also told reporters that within days of a Security Council resolution in December 1990 authorizing the United States to wage war against Iraq, the Government of President Saddam Hussein loaded anthrax, botulin and another toxic agent on nearly 200 bombs and warheads and began deploying the weapons at bases inside Iraq. Threats by President Bush and his Secretary of State, James A. Baker 3d, to strike Iraq with huge retaliatory bombings if Baghdad used chemical weapons seem to have persuaded President Hussein not to use the biological arms, officials and diplomats said today.

The biological weapons had the potential to wreak enormous damage. Scientists cannot predict how such weapons would perform in practice because of uncertainty about how weather and other factors would influence the dispersal of the deadly agents.