President Reagan has decided on military retaliation against Iran for the Iranian missile attack on a U.S.-flagged ship off Kuwait on Friday, administration officials said last night.

A White House official said it would be a "measured response" to the Iranian attack but gave no other details. Another official said the U.S. action would be "proportionate" to the Iranian action.

The president called congressional leaders to the White House about 7:45 p.m. to inform them of his decision. The meeting continued until about 9 p.m.

Officials refused to provide any details late last night, and participants were not available or refused to comment. Among those included in the meeting were House Speaker Jim Wright (D-Tex.), Senate Majority Leader Robert C. Byrd (D-W.Va.), House Majority Leader Thomas S. Foley (D-Wash.), Senate Minority Leader Robert J. Dole (R-Kan.) and White House chief of staff Howard H. Baker Jr.

A White House official said announcement of the president's decision would probably not be made until early today because of "elements of risk" that U.S. forces involved in carrying out the retaliatory action might incur if the Iranians were informed of any details.

This seemed to suggest that U.S. retaliation was imminent.

Returning to the White House shortly after 4 p.m. yesterday from Bethesda Naval Medical Center, where his wife, Nancy, underwent surgery for breast cancer Saturday, Reagan told reporters who asked if he had made a decision on whether to retaliate, "I've made it."

Asked what decision he had reached, Reagan shouted, "I can't tell you."

Earlier in the day, the president was asked if he had decided to order an attack on the Iranian missile site on Faw Peninsula in Iranian-captured Iraqi territory. "If I told you, I'd be telling them," he replied, referring to the Iranians.

The Iranian missile that hit the Sea Isle City, a Kuwaiti tanker flying the American flag, is believed to have been fired from Faw, which is 50 to 60 miles to the north.

Reagan made his decision after a weekend of meetings involving lower-level officials who worked on various options drawn up by Pentagon planners in seeking to deal with the escalating Iranian military threat to U.S. commercial shipping in the gulf.

On Thursday, another Iranian missile apparently fired from Faw hit a U.S.-owned tanker, the Sungari, which was flying a Panamanian flag and therefore did not fall under the protection of U.S. military forces.

In Friday's attack on the Sea Isle City, its American captain, John Hunt, was blinded and 17 other crew members were wounded.

Reagan was initially presented with the options at a meeting Friday with his top national security advisers. Newsweek magazine reported yesterday that Reagan had told them that any retaliatory strike against Iran must be "proportionate and measured" and aimed only at military targets.

The United States had to demonstrate decisively Washington's political will to retaliate for the attack on the Sea Isle City, Reagan told his advisers according to the magazine.

One of the options under review was reported to be a limited air strike by A6 attack planes from the carrier USS Ranger against the Iranian Silkworm batteries located at Faw and around the delta of the Shatt al Arab waterway at the northern end of the gulf.

The chairman of the Senate Armed Services Committee, Sam Nunn (D-Ga.), said the administration had the right to retaliate against Iran.

"I think we have every right to take out the {Iranian} Silkworm missiles," Nunn told Cable News Network yesterday.

"If the president decides to take a response and it is proportionate, I will support it," Nunn said.

Iranian President Ali Khamenei said, meanwhile, that he doubted the United States was in position to take violent action against Iran in the gulf, Tehran radio reported this morning.

The U.S. government "is in a very difficult situation now and it is not clear if it has the necessary elements for a violent action," the radio quoted him as saying in an interview with the English-language daily Tehran Times.

Khamenei said the U.S. government had to take some action to demonstrate its authority, "but on the other hand any violent act in the Persian Gulf will greatly harm long-term U.S. interests," the radio, monitored in Nicosia, Cyprus, reported.

In Kuwait, the government said after an emergency Cabinet meeting that it had adopted a plan to "deal seriously and effectively with Iran's recent aggressive violations and practices," Washington Post correspondent Patrick E. Tyler reported from Kuwait City.

There was no elaboration on what steps the sheikhdom's rulers will take to meet what it called the "extremely dangerous developments" in the gulf war, Tyler reported.

Kuwait's ruling family is known to have been in close consultation with Washington throughout the weekend. In addition, Secretary of State George P. Shultz held consultations Saturday in Jeddah with Saudi Arabia's King Fahd.

The Saudis have been pressing the United States to take firm action in response to the Iranian missile attack.

After their meeting, Shultz hinted some action would be forthcoming. "When we have decided to take action and have taken it, you will know what it is," he said.

Throughout most of yesterday there was a surface calm in Arab capitals and here. But a senior officer of the U.S. Central Command, Brig. Gen. Jed Pearson, arrived in Kuwait for consultations with the defense minister, Sheikh Salem al-Sabah, Tyler reported.

U.S. Ambassador to Bahrain Sam Zakhem was recalled to the United States to discuss the gulf situation, U.S. Embassy officials said.

Four U.S. Navy warships were reported to have passed through the Suez Canal yesterday. Pentagon officials said they were part of a normal rotation of ships making up the armada of 36 U.S. warships and vessels now stationed inside the gulf or outside in the northern Arabian Sea.

In Kuwait, officials were buoyed by the perceptible hardening of U.S. statements about possible military retaliation against Iran.

Kuwait has refused to grant U.S. military forces access to bases or naval facilities, but several high-ranking U.S. officials recently have praised Kuwait, along with Saudi Arabia and Bahrain, for their cooperation with the American military presence in the region.

Kuwait has become uneasy in its support for the U.S. presence in the gulf, as officials have recognized that their high-stakes gambit to invite superpower protection for their oil tanker fleet has brought Kuwait ever closer to the battleground in the seven-year-old Iran-Iraq war.

At a gathering of Kuwaiti intellectuals and business leaders last night, there was support for strong U.S. military action against Iran. But at the same time, there was also uniform opposition to bringing Kuwait into the conflict by turning the country into a base for U.S. military forces.

The apprehension against such a step, these Kuwaitis explained, stemmed from a widespread perception that American strategic priorities in the region are focused primarily on preventing the Soviet Union from gaining an advantage. In their eyes, America's interest in the overall security of the moderate Arab states is subordinate to this larger goal.

Their unwillingness to deepen their commitment to the United States, they say, is a hedge against a possible pullout from the gulf by the United States, or a secret policy reversal, such as the decision to sell arms secretly to Iran last year, that will leave the Arabs ultimately exposed to their hostile Persian neighbor.

Meanwhile, the U.S.-flagged supertanker Bridgeton, the largest crude oil tanker in the reflagged Kuwaiti tanker fleet under U.S. Navy protection, left drydock in Dubai after repairs for mine damage.

The Bridgeton was damaged by a contact mine July 24 during the first U.S. Navy convoy escort through the 550-mile gulf waterway.

Iran reported that its warplanes bombed Iraqi troop concentrations on the southern war front. Tehran's state news agency also reported that it shot down three Iraqi planes this weekend during bombing raids on industrial targets in southern and northwestern Iran. Iraq acknowledged losing one plane.

Senior Iranian officials launched their own diplomatic drive this weekend, with Prime Minister Mir Hossein Mousavi reported in Damascus for talks with Syrian leaders and Foreign Minister Ali Akbar Velayati on his way to Cuba and Nicaragua.