The White House announced yesterday that U.S. officials had received fresh assurances from Iran "within the last 24 hours" that all Iraqi warplanes seeking sanctuary in Iran would remain impounded until the end of the Persian Gulf War, and a top Iranian diplomat said there were no circumstances in which Tehran would release the planes before then.

White House spokesman Marlin Fitzwater said the Iraqi jets -- now numbering more than 90 -- "will be watched continually" by the allies, and U.S. military officials vowed to destroy them if they leave Iranian sanctuaries. Iran also has been reminded by Britain and other governments that Tehran's neutrality in the conflict precludes refueling the Iraqi fleet or aiding its reentry into battle, diplomatic sources said.

Iran's U.N. ambassador, Kamal Kharrazi, said last night, "These airplanes are seized and they will be seized until the war is over." Asked in a televised CBS News interview whether even Israel's entry into the war could change his government's commitment, he said that "liberation of Palestine does not justify occupation of Kuwait." He also rejected Iraqi President Saddam Hussein's assertion that the confrontation over Kuwait is "a war between believers and infidels."

U.S. government and allied analysts continued to puzzle over the exodus of Iraqi warplanes into Iran, among the most surprising developments in two weeks of war. Most of those interviewed saw Baghdad's motive as desperation in the face of systematic bombing of a largely grounded air force. Tehran's offer of sanctuary to a once-bitter enemy was generally viewed as a bid for power and influence in shaping Persian Gulf security arrangements after the war.

The escape of Iraq's aircraft began last week with the flight of a small group that included the only surviving Iraqi radar early warning plane, known as the Adnan 2, U.S. and Arab sources said. Even before the war began, Saddam had flushed some of his commercial airliners to Libya, Mauritania and, eventually, Iran, the sources added.

Military transport planes, escorted to the border by Iraqi fighters, subsequently fled to Iran. At first, the fighter escorts turned back before entering Iranian airspace and returned to their bases, the sources said. But beginning late last week, the fighters began fleeing themselves. Iranian interceptors, apparently confused about the intruders' intent, scrambled and chased away the first Iraqi fighters crossing the border. But subsequent fighters, now numbering about 65, were permitted to land unimpeded.

U.S. officials are uncertain whether Saddam is controlling the exodus, although he is believed to concur in the strategy, particularly after the allies found that it was easier than expected to destroy hardened Iraqi aircraft shelters with 2,000-pound bombs.

"When we began to earnestly hit the planes inside their hardened shelters, yes, they started to flee," a senior Pentagon official said last night. "I think it would be irresponsible for me to say for certain that's why they started to flee. But there is that unmistakable sequence."

The mass flight of Iraqi planes to Iran was widely viewed by the allies as "more a sign of weakness than a sign of some devious plot," Lt. Gen. Thomas Kelly, senior operations officer for the Joint Chiefs of Staff, told reporters yesterday. Although the exodus represents a significant fraction of the best Iraqi jets, "a large number of first-class aircraft" remain in Iraq, Kelly said at the Pentagon's daily press briefing on the war.

Kelly said the escaping Iraqi jets, estimated yesterday to have grown in number by about 10 from the day before, had no guarantee of safe passage from the allies.

Thus far, he said, the Iraqi planes had chosen to bolt for Iran when out of range of allied fighters. But "if we find enemy aircraft in Iraqi airspace or Kuwaiti airspace," the general told reporters, "we will engage them and shoot them down."

A senior diplomat from an Arab country fighting Iraq said here yesterday that the first Iraqi warplane flights to Iran "really shook us."

He said Iran had been warned that if the Iraqi planes return to combat -- a move that would require refueling and maintenance in Iran -- then Tehran would be held accountable. "If those aircraft fly, that's it. Iran is involved in the war," he predicted.

"The Iranians know they cannot con us. They cannot say, 'Sorry, they took off.' There is no way.

And we put them on notice: Please don't get involved," the diplomat added. "We were diplomatically clear."

U.S. confidence in Tehran's pledge of neutrality is based on an assumption that Iran wants to avoid angering other nations that have military forces committed to the coalition, an American official said.

"Even though there are no warm feelings for America, Iran would alienate many others with whom it would like better relations."

A number of analysts said yesterday that the latest twist in the gulf war has significance beyond the military value of removing a sizable number of Iraq's planes from combat. These analysts said Iran, which was destitute when its eight-year war with Iraq ended two years ago, now appears to be bidding for leverage and a larger role for itself in the near term as Iraq faces a costly fight with the U.S.-led coalition.

A senior government official said Iran had sent numerous messages to Washington, including some in which the Soviet Union served as intermediary, promising not to return the warplanes to Iraq during the conflict or perhaps at all. Saddam is "not going to get them back," the official said.

Charles Kupchan, a Persian Gulf specialist at Princeton University, said, "This should not be seen as a sign that Iran wants to become involved or will side with Iraq."

He said, "They are carefully playing this in an effort to enhance their role in the gulf, to become an actor in this war diplomatically, rather than a passive bystander."

More immediately, by granting sanctuary to the planes, Iran gains leverage with Washington. "It means the United States is making overtures to the Iranians to make sure they don't let these aircraft reenter the war," Kupchan said. "It's a risk-free way for the Iranians to play a role."

The senior Arab diplomat in Washington described Iran's motives in more cynical terms, saying Tehran is giving Saddam just enough rope to hang himself.

The Iranians, he said, "want to destroy Saddam Hussein, but they're scared to death he will do the right thing" and pull Iraqi forces out of Kuwait before he is defeated, the diplomat said.

He recalled that Iran earlier allowed some food to be shipped to Saddam, despite United Nations sanctions, "to give him the sense of confidence."

By the same token, Iran's leadership now intends to give Saddam a false sense of security that his planes are safe and possibly can be used another day, the diplomat said. The goal of Iran's leadership is to make Saddam "stay obstinate" and then get "clobbered" by the allied coalition, he added. Referring to the Iranians, he said, "they want him destroyed."

Although government officials here said they have few clues as to why the planes flew to Iran, some officials surmised that the move may reflect a pre-war deal reached when Iraqi Foreign Minister Tariq Aziz made a conciliatory visit to Tehran last September.

James A. Bill, director of the Reves Center for International Studies at the College of William and Mary and author of a study of U.S.-Iran relations, said Iran's decision to harbor the planes is an important signal to the outside world, as well as a possible internal political gambit.

"The Iranians feel they have been shoved aside with respect to resolution of the gulf crisis," he said. "They are ignored and upset and angry, and they consider themselves the superpower of the gulf. {They think} how can there be a resolution without them."

Bill said the planes could also help Iran's leadership answer internal criticism from more radical factions. "There is some discontent and unease about the fact that a fellow Muslim country is being battered and beaten by a colossal Western alliance. This is something small they can do to indicate there is a sense of Islamic brotherhood," he said.

Michael Hudson, a professor at Georgetown University's School of Foreign Service, said: "We were thinking Iran would be sitting back and clapping their hands while we beat the hell out of the Iraqis. But now it seems their reaction is more complex. They realize that

a total power vacuum, while it offers some opportunities, it complicates their lives as well. They are playing a consummately skilled game."