A U.S. Navy fighter plane last weekend fired two missiles at an Iranian aircraft "perceived" to be threatening an unarmed U.S. patrol plane flying over the Navy escort of Kuwaiti oil tankers through the Strait of Hormuz, administration sources said yesterday.

Both missiles fired by the Navy F14 Tomcat fighter apparently missed their target, sources said. But the firing is believed to be the first direct hostile act by U.S. forces against Iranian military forces in years, and marks a significant moment in the long confrontation between the United States and the Iranian regime of Ayatollah Ruhollah Khomeini.

Sources said the episode began when a suspected Iranian warplane approached a U.S. P3 surveillance plane while the convoy of three reflagged tankers and three U.S. warships steamed into the troubled Persian Gulf.

The P3 aircraft "was perceived to be threatened" by the approaching contact, and warnings to stay away were issued by U.S. forces, sources said. But the intruder airplane did not respond, sources said.

"It was warned, it did not respond, it kept coming," said one source familiar with the incident.

The F14 from the USS Constellation providing air cover for the escort operation then fired two Sparrow air-to-air missiles at the oncoming aircraft, sources said. The intruder aircraft banked sharply, and the two missiles apparently missed the plane, sources said. The strange aircraft, which was seen by radar but not by U.S. pilots, then flew away. Sources said it is unclear whether the Iranian plane locked its electronic weapons control systems onto any U.S. aircraft.

Reports of the incident emerged hours after Pentagon officials reported yesterday that an Iranian aircraft had been conducting surveillance missions over the convoy operation, but the officials made no disclosures of the missile firing by the U.S. plane. Although sources declined to identify the type of Iranian aircraft conducting the surveillance, the Iranian air force includes F14 fighter jets purchased from the United States before the fall of Shah Mohammad Reza Pahlavi.

The information about this incident was tightly held and even kept from a number of key administration officials so it would not emerge during any of the official briefings at the White House yesterday. No information about the incident was given out in the regular daily briefings at the State Department and Pentagon.

At the White House briefing yesterday morning, spokesman Marlin Fitzwater was sharply questioned about whether administration officials had put out a false story last week giving misinformation about the timing of U.S. naval convoys in the gulf.

Fitzwater said he knew of no attempt by the administration to deliberately mislead reporters and suggested that they go back to their sources.

He said that any reporter who used an anonymous source was "running a risk," and added that he and Secretary of State George P. Shultz had said there was no change in the timing of the convoys.

But last night, after the missile firing incident was disclosed, White House officials declined even to comment publicly on the report, or to say whether they had misled reporters earlier in the day when they said there was no "disinformation campaign."

The 510-pound Sparrow is a semiactive radar interceptor missile, which means it is guided to the target partially by the launching aircraft and partially by its internal radar.

The Sparrow has been a standard weapon for years. Experts say that it is less accurate than more modern missiles. Sources said the rules of engagement for attack in the gulf require that the plane be well within the Sparrow's 65-mile range.

The U.S. Navy's commander of the Middle East Task Force, which is conducting the gulf operations, was so concerned about potential air attacks that he requested the Navy's most sophisticated air defense ship, an Aegis cruiser, to accompany the convoy through the Strait of Hormuz.

U.S. officials have been particularly concerned with the potential threat of Silkworm antiship missiles aimed at ships passing through the narrow strait. Several missile-launching sites have been detected by intelligence sources. During a convoy out through the strait last week, U.S. officials believed they had detected activity at one of the Silkworm launch sites and prepared for a possible attack. Pentagon sources said it turned out to be a "false alarm" and there was no immediate threat.

Pentagon spokesman Robert B. Sims yesterday refused to say whether U.S. intelligence sources detected any Silkworm missile activity during the escorting operation last weekend.

The convoy was delayed temporarily yesterday while the U.S. Navy conducted mine-hunting operations in the northern gulf ahead of the tankers and their U.S. escorts.

Pentagon officials in recent days have attempted to tighten leaks to the news media both about operational details of the escorting mission and about details of incidents that occurred during the operations.

Last week Defense Secretary Caspar W. Weinberger circulated a memorandum to top Pentagon officials cautioning, "Please give your full support and cooperation to maintaining security and remembering 'loose lips sink ships.' "