Those officers, most of whom agreed to speak on the condition that they not be identified, spoke in response to a reporter's questions about the nature of gas warfare on both sides of the conflict between Iran and Iraq from 1981 to 1988. Iraq's use of gas in that conflict is repeatedly cited by President Bush and, this week, by his national security adviser, Condoleezza Rice, as justification for "regime change" in Iraq.

The covert program was carried out at a time when President Reagan's top aides, including Secretary of State George P. Shultz, Defense Secretary Frank C. Carlucci and Gen. Colin L. Powell, then the national security adviser, were publicly condemning Iraq for its use of poison gas, especially after Iraq attacked Kurds in Halabja in March 1988.

During the Iran-Iraq war, the United States decided it was imperative that Iran be thwarted, so it could not overrun the important oil-producing states in the Persian Gulf. It has long been known that the United States provided intelligence assistance to Iraq in the form of satellite photography to help the Iraqis understand how Iranian forces were deployed against them. But the full nature of the program, as described by former Defense Intelligence Agency officers, was not previously disclosed.

Secretary of State Powell, through a spokesman, said the officers' description of the program was "dead wrong," but declined to discuss it. His deputy, Richard L. Armitage, a senior defense official at the time, used an expletive relayed through a spokesman to indicate his denial that the United States acquiesced in the use of chemical weapons.

The Defense Intelligence Agency declined to comment, as did Lt. Gen. Leonard Perroots, retired, who supervised the program as the head of the agency. Mr. Carlucci said, "My understanding is that what was provided" to Iraq "was general order of battle information, not operational intelligence."

"I certainly have no knowledge of U.S. participation in preparing battle and strike packages," he said, "and doubt strongly that that occurred."

Later, he added, "I did agree that Iraq should not lose the war, but I certainly had no foreknowledge of their use of chemical weapons."

Though senior officials of the Reagan administration publicly condemned Iraq's employment of mustard gas, sarin, VX and other poisonous agents, the American military officers said President Reagan, Vice President George Bush and senior national security aides never withdrew their support for the highly classified program in which more than 60 officers of the Defense Intelligence Agency were secretly providing detailed information on Iranian deployments, tactical planning for battles, plans for airstrikes and bomb-damage assessments for Iraq.

Iraq shared its battle plans with the Americans, without admitting the use of chemical weapons, the military officers said. But Iraq's use of chemical weapons, already established at that point, became more evident in the war's final phase.

Saudi Arabia played a crucial role in pressing the Reagan administration to offer aid to Iraq out of concern that Iranian commanders were sending waves of young volunteers to overrun Iraqi forces. Prince Bandar bin Sultan, the Saudi ambassador to the United States, then and now, met with President Saddam Hussein of Iraq and then told officials of the Central Intelligence Agency and the Defense Intelligence Agency that Iraq's military command was ready to accept American aid.

In early 1988, after the Iraqi Army, with American planning assistance, retook the Fao Peninsula in an attack that reopened Iraq's access to the Persian Gulf, a defense intelligence officer, Lt. Col. Rick Francona, now retired, was sent to tour the battlefield with Iraqi officers, the American military officers said.

He reported that Iraq had used chemical weapons to cinch its victory, one former D.I.A. official said. Colonel Francona saw zones marked off for chemical contamination, and containers for the drug atropine scattered around, indicating that Iraqi soldiers had taken injections to protect themselves from the effects of gas that might blow back over their positions. (Colonel Francona could not be reached for comment.)

C.I.A. officials supported the program to assist Iraq, though they were not involved. Separately, the C.I.A. provided Iraq with satellite photography of the war front.

Col. Walter P. Lang, retired, the senior defense intelligence officer at the time, said he would not discuss classified information, but added that both D.I.A. and C.I.A. officials "were desperate to make sure that Iraq did not lose" to Iran.

"The use of gas on the battlefield by the Iraqis was not a matter of deep strategic concern," he said. What Mr. Reagan's aides were concerned about, he said, was that Iran not break through to the Fao Peninsula and spread the Islamic revolution to Kuwait and Saudi Arabia.

Colonel Lang asserted that the Defense Intelligence Agency "would have never accepted the use of chemical weapons against civilians, but the use against military objectives was seen as inevitable in the Iraqi struggle for survival." Senior Reagan administration officials did nothing to interfere with the continuation of the program, a former participant in the program said.

Iraq did turn its chemical weapons against the Kurdish population of northern Iraq, but the intelligence officers say they were not involved in planning any of the military operations in which those assaults occurred. They said the reason was that there were no major Iranian troop concentrations in the north and the major battles where Iraq's military command wanted assistance were on the southern war front.

The Pentagon's battle damage assessments confirmed that Iraqi military commanders had integrated chemical weapons throughout their arsenal and were adding them to strike plans that American advisers either prepared or suggested. Iran claimed that it suffered thousands of deaths from chemical weapons.

The American intelligence officers never encouraged or condoned Iraq's use of chemical weapons, but neither did they oppose it because they considered Iraq to be struggling for its survival, people involved at the time said in interviews.

Another former senior D.I.A. official who was an expert on the Iraqi military said the Reagan administration's treatment of the issue — publicly condemning Iraq's use of gas while privately acquiescing in its employment on the battlefield — was an example of the "Realpolitik" of American interests in the war.

The effort on behalf of Iraq "was heavily compartmented," a former D.I.A. official said, using the military jargon for restricting secrets to those who need to know them.

"Having gone through the 440 days of the hostage crisis in Iran," he said, "the period when we were the Great Satan, if Iraq had gone down it would have had a catastrophic effect on Kuwait and Saudi Arabia, and the whole region might have gone down. That was the backdrop of the policy."

One officer said, "They had gotten better and better" and after a while chemical weapons "were integrated into their fire plan for any large operation, and it became more and more obvious."

A number of D.I.A. officers who took part in aiding Iraq more than a decade ago when its military was actively using chemical weapons, now say they believe that the United States should overthrow Mr. Hussein at some point. But at the time, they say, they all believed that their covert assistance to Mr. Hussein's military in the mid-1980's was a crucial factor in Iraq's victory in the war and the containment of a far more dangerous threat from Iran.

The Pentagon "wasn't so horrified by Iraq's use of gas," said one veteran of the program. "It was just another way of killing people — whether with a bullet or phosgene, it didn't make any difference," he said.

Former Secretary of State Shultz and Vice President Bush tried to stanch the flow of chemical precursors to Iraq and spoke out against Iraq's use of chemical arms, but Mr. Shultz, in his memoir, also alluded to the struggle in the administration.

"I was stunned to read an intelligence analysis being circulated within the administration that `we have demolished a budding relationship (with Iraq) by taking a tough position in opposition to chemical weapons,' " he wrote.

Mr. Shultz also wrote that he quarreled with William J. Casey, then the director of central intelligence, over whether the United States should press for a new chemical weapons ban at the Geneva Disarmament Conference. Mr. Shultz declined further comment.