What was being portrayed as an incident of international gamesmanship may have turned into a first-class gaffe yesterday, as U.S. officials scrambled to kill a report that an Iranian Air Force fighter intercepted the jet carrying national security adviser Zbigniew Brzezinski from Pakistan to Saudi Arabia.

U.S. officials in Washington said the plane that intercepted the U.S. Air Force jet above the Gulf of Oman was an American Navy fighter and not -- as had been reported by the plane's pilot earlier Monday -- an Iranian F14.

A Defense Department spokeman said the U.S. fighter was based aboard an aircraft carrier in the Persian Gulf region, and that it had flown to within 2.5 miles of the Brzezinski plane to "make a routine identification" of the aircraft.

The story began when a chess game between Brzezinski and a reporter was interrupted by a handwritten note from an aide, Air Force Col. Leslie Denend. The note, marked "Zbig Eyes Only," informed the security adviser of the incident.

An officer aboard the plane later said it was possible the pilot could have been mistaken, since he could not see the markings of the interceptor. He could say for certain, however, that the plane was an F14. The Pentagon has confirmed that it was an F14.

Iran bought 80 F14s from the United States when the now-deposed shah was still building up Iranian military strength as a policeman for the strategic Persian Gulf region.

Earlier, top U.S. officials aboard the plane -- which carried Brzezinski, Deputy Secretary of State Warren Christopher and others -- said the jet clearly violated international air traffic control regulations, and speculated that Iran had taken the opportunity to show its military was not as powerless as it was believed to be.

The fact that the jet had been identified as an Iranian jet is likely to cause embarrassment in Washington, where officials expressed concern this morning that the story could upset the delicate negotiations to release the estimated 50 hostages at the U.S. Embassy in Tehran.

[A Defense Department spokesman said U.S. officials have believed Iran's capability to maintain the remaining 77 F14s in their Air Force had been impaired because of the revolution and continuing unrest, particularly among the military. He added that because of lack of access to Iran to gather information, the Pentagon could not estimate how many of the planes were airworthy. There have been several reports that Iranian F14 have been flown, he said.]

The incident took place at about 10 a.m. Saudi time, as the Air Force jet was leaving Pakistan and flying over the Gulf of Oman. It was well over international waters off Iran's coast, near the port of Chag Bahar, where the deposed shah of Iran had planned to build a giant naval base.

The area is of immense strategic importance, especially since the Soviet-backed coup in Afghanistan Dec. 27 put Red Army troops within 400 miles of the vital Gulf of Oman.

After arriving in Riyadh, the Saudi capital, Brzezinski and Christopher met for a working lunch with Saudi Foreign Minister Prince Saud.Later they had a two-hour meeting with Prince Saud and Crown Prince Fahd. Administration officials here said they planned to meet with Saudi leaders again Tuesday morning.

A U.S. delegation official refused to go into details on the meetings, but he said it was clear that Carter's State of the Union declaration that this area was part of the United States' vital interests, was "a new, vital, positive element in U.S.-Saudi relations."

The Saudis have been complaining that Washington was not standing firm in the face of political developments in this area, including the fall of the shah of Iran last year. The saudis, however, have refused to help the Americans establish new military bases in this area, preferring, as one diplomat here said, to have the United States station their planes and troops somewhere else.

"It's like a neighborhood where everybody wants a fire station nearby so their insurance bills go down, but they don't want to have it so close that they hear the sirens every night," a diplomat here said.

There was no indication tonight whether the Saudis have changed their mind about allowing a greater U.S. military presence in this area.