U.S. military leaders preparing for possible combat with Iraq have decided against using nuclear or chemical arms to destroy Iraqi military installations or retaliate against Iraqi poison gas or germ warfare attacks, according to senior U.S. officials.

The decision not to use "weapons of mass destruction" in the Middle East crisis reflects high confidence in the overwhelming firepower of U.S. conventional forces, plus a desire not to compound the already unpredictable political consequences of a potential military conflict, the officials said.

Some nuclear weapons are stored aboard U.S. naval vessels now in the Persian Gulf and surrounding waters, but no effort has been made to deploy nuclear or chemical arms in Saudi Arabia or incorporate them in U.S. planning for a possible military engagement, the officials said.

President Bush and other officials have said that the United States would respond in the strongest possible way to an Iraqi attack using deadly germs or chemicals. Defense Secretary Richard B. Cheney said during a Dec. 23 visit to the gulf that "were Saddam Hussein foolish enough to use weapons of mass destruction, the U.S. response would be absolutely overwhelming and it would be devastating." But administration officials say such forceful language should not be interpreted as meaning the United States plans to use nuclear or chemical weapons.

A knowledgeable official said over the weekend that the idea of using nuclear or chemical weapons "has never been on the table" in discussions involving top policy-makers at the White House. He said the ambiguity of the administration's public statements has been intended to maintain pressure on Saddam by appearing to leave open every military option.

Some junior U.S. military officers in Saudi Arabia have advocated using, or at least threatening to use, nuclear weapons as a means of coercing an Iraqi withdrawal or early surrender that would avoid significant American casualties in an extended ground assault on Iraqi forces entrenched in southern Kuwait.

"Why wait around?" asked John Berrie, a U.S. Army captain in Saudi Arabia making the case for a nuclear attack.

"16 January, on the dot, if he isn't out of there, we want to see a {nuclear} mushroom {cloud}," another American field officer said in a recent conversation with a reporter, referring to the Jan. 15 deadline for Iraq's withdrawal, after which the U.N. Security Council has authorized the use of force.

Some officers have questioned why they should risk their lives in a potentially bloody assault against Iraqi forces when tactical nuclear weapons could be used. In 1945, for instance, President Harry S. Truman authorized nuclear attacks on two Japanese cities as a means of shortening the war and saving American lives by coercing an unconditional Japanese surrender.

But a senior military official, who spoke on condition of anonymity, said he did not "see a moral parallel" between Truman's action and the current confrontation in the gulf. "The world is more complicated now, and the consequences of using tactical nukes -- some of which are unpredictable -- outweigh their military utility," the official said. These drawbacks could include offending our allies and "destroying Kuwait in order to save it," he added.

In 1978, then-Secretary of State Cyrus R. Vance told a United Nations special session on disarmament that the United States would not use nuclear weapons "against any non-nuclear weapons state party to the NPT," or Nuclear Non-Proliferation Treaty -- a policy that officials say still stands. Iraq signed the NPT in 1968.

According to Greenpeace, an activist group that attempts to track the deployment of nuclear weapons on military vessels worldwide, more than 500 nuclear weapons may already be deployed on the roughly 40 major U.S. Navy surface combat ships and submarines in the Middle East. The estimate is based on public estimates of routine, peacetime nuclear deployments.

Defense officials declined to disclose the actual number in the region but said that some nuclear weapons had been removed from ships so they could accommodate additional conventional arms.

The officials also said U.S. Army units that have custodial responsibility for tactical nuclear artillery and missiles in Europe have been deliberately left behind during the massive, continuing transfer of arms and combat personnel from Europe to the Middle East.

A knowledgeable official said this situation reflects an early, informal agreement between Washington and Riyadh that Saudi officials "would not ask" about the possible use of tactical nuclear weapons or prohibit their deployment on Saudi soil, and the United States "would not tell" its precise plans but also "would not bring" such weapons into the desert.

A senior Army official, speaking on condition that he not be named, said no U.S. chemical arms have been moved to the region. The Air Force recently conducted flight tests to verify that its F-16 fighters -- some of which are deployed in the Persian Gulf -- can spray poison gas from special tanks produced decades ago and kept on standby since then. But officials say the program was initiated before Iraq's Aug. 2 invasion of Kuwait and has not been stepped up.

The United States has no biological weapons.

In an interview with the Christian Science Monitor on Aug. 14 when he was still Air Force chief of staff, Gen. Michael J. Dugan said that the United States "would avoid in every possible circumstance even talking about deploying or using chemical weapons. . . . We've made a national policy of getting rid of" such arms. Dugan was fired on Sept. 17 for disclosing details of U.S. attack plans.

Officials said CIA Director William H. Webster reflected what is still the dominant administration view in a Dec. 14 statement to The Washington Post that "we do have massive conventional warfare capability there {in the gulf} with no reason to believe that they could not do what was expected of them." Webster added that use of this conventional capability would be understandable to other nations in the region, but "when you get Western use of chemical weapons or other non-conventional weapons, I think you invite a new dimension that may carry heavy costs . . . in future relationships."

Webster emphasized that "the way that we proceed {in any combat} has to have, in my view, concerted support from those who asked us to come, and not be appalling to them." Webster indicated it was his view that a U.S. decision to breach a 45-year-old taboo against nuclear weapons use would be seen as so "appalling" it should not be considered in the crisis.

Further indicating that administration officials have had little interest in planning to use anything other than conventional arms against Iraq, Cheney in November told a proponent of nuclear weapons use that "in the more than three months now that we've been dealing with the crisis, you are the first individual who's suggested to me that approach."

Stan Norris, a senior staff analyst at the Natural Resources Defense Council, noted that the wisdom of using the atomic bomb against Japan is still being debated 45 years later. "Using nuclear weapons in the gulf would blacken America's name for decades to come," he said.