Faced with mounting criticism from the United States, U.N. Secretary General Kofi Annan's point man in Baghdad said he is leaving Iraq after a 16-month stint that has been marked by often bitter relations with Washington.

The departure of the Indian diplomat, Prakash Shah, comes more than a week after the United States formally complained to Annan about Shah's handling of a recent mission to Baghdad to clean up a U.N. chemical weapons testing laboratory. Clinton administration officials charged Shah with turning a routine technical mission into an inquisition of UNSCOM, the U.N. Special Commission charged with ridding Iraq of weapons of mass destruction.

Shah said his departure from Baghdad was decided months ago and was not prompted by American pressure. He said he will return to his home in New Delhi and remain available to take on U.N. missions to Baghdad, if asked.

But Shah also said that with the U.N. disarmament effort in a deep freeze and the Security Council deeply divided over Iraq policy, there is little for him to do in Baghdad. "There was no point to my staying on," he said.

Ever since Shah's appointment as Annan's personal representative to Baghdad in March 1998, the Clinton administration has viewed him as a partisan in Iraq's campaign to obtain relief from U.N. sanctions. And U.S. officials made it clear they were happy to see him go.

The Clinton administration said Shah crossed the line last month by excluding U.S. and British representatives from a team of arms experts assigned to destroy mustard gas and nerve gas samples, including a small amount of the highly lethal nerve agent VX, kept in refrigerators at UNSCOM's Baghdad headquarters.

The acting U.S. representative at the United Nations, Peter Burleigh, complained in a July 28 letter to Annan that the United States had been misled by his aides into believing that the head of the U.S. interest section in Baghdad, a Polish diplomat, had been invited to participate in the mission. Instead, Shah invited representatives from Russia, France and China, three countries that favor lifting sanctions on Baghdad.

"Representatives from China, France and Russia were selected in an opaque manner and were allowed to interfere and delay the work of technical workers," Burleigh wrote. The U.S. representative, he added, "was never invited by Ambassador Shah to participate in the observer mission."

Russian officials voiced suspicions, first raised by Iraq, that UNSCOM may have used the vials of VX stored at its headquarters to taint Iraqi warheads, like a police officer planting evidence on a suspect.

France and China have since called on the Security Council to demand that UNSCOM provide a full explanation, complete with log books and lab records, of how the VX was used. The United States has blocked the move, arguing that it would be a pointless diversion from UNSCOM's main business, disarming Iraq.

UNSCOM officials say the samples were used to calibrate sophisticated laboratory testing equipment. The team of experts that conducted the recent mission to Baghdad concluded that it was "probable" that the VX was used for calibration purposes, although "this could not be established definitively."

Shah said he had not sought to exclude Americans from the mission.

"I isolated the Americans?" he asked incredulously, insisting that he had extended an invitation to the U.S. representative. "I would love to be powerful enough to isolate the most powerful country in the world. The United States is putting too much power in my elbow."

He added that any disagreements over his approach to Iraq derived from his concern with easing the suffering caused by nearly a decade of economic sanctions.

"I am not the special envoy of the United States, I'm the special envoy of the U.N. secretary general," he said. "We have to look at the entire picture, and that picture includes 22 million civilians."