The first combat missions ever flown by the U.S. Air Force's newest and hottest jet fighter-bomber, the F15. were flown by Israeli pilots this week during the combined land, air and sea attack against Palestinian guerrilla bases in southern Lebanon.

Israel is the only foreign country thus far to get the highly sought twinjet warplane from the United States. The fact that its first combat use came during the controversial Israeli assault across Lebanan's border could add to the dispute - already growing in Washington about further sales of the plane in the Middle East.

The Carter administration, in a package deal that Israel bitterly opposes, wants to sell 60 F15s for the first time to Saudi Arabia and 50 less potent F5 jets to Egypt. It would also provide Israel with 15 more F15s and 75 F16s, fewer than Jerusalem wants.

The Israeli Air Force has received U.S.-built F-4 Phantom and A4 Skyhawk jets for years. The F15 is the most powerful replacement available for those aging warplanes, and has become a symbol of shifting American arms export policies in the Middle East.

In recent days, a pro-Israel majority of the House International Relations Committee asked President Carter not to formally submit the new arms package to Congress, while Saudi Arabia warned the White House that any major delay would cause them to look elsewhere for advanced warplanes.

The Israeli newspaper Maariv yesterday reported that the F15s had taken part for the first time in combat operations here by bombing guerrilla outposts.

Last night, however, Israeli Chief of Staff Lt. Gen. Mordechai Gur, perhaps anticipating sensitivity over the planes' operations, said during a television appearance that the plane's role was to provide "movable radar," suggesting that its mission was only air support.

There are signs that the use of the F15 over Lebanon could become sensitive for Washington. Israeli Prime Minister Menachem Begin has stressed that the attack was taken in "self-defence" after repeated after repeated Palestinian terrorist attacks, including the one that left 45 dead after a bus hijacking eight days ago.

If Israel continues to occupy the six-mile wide strip across southern Lebanon and the F15 continues to be used, then critics may argue that arms are being used for purposes other than self-defense.

The F15 actually had already earned a place in modern Israeli history before it ever took off on its first combat mission.

In December 1976, the first two of 25 F15s promised by the United States were flown here by American pilots for delivery. But they arrived late and an arrival ceremony was delayed. This caused members of the National Religious Party, at the time part of the coalition government of former prime Minister Yitzhak Rabin, to complain that they could not get home before sundown on the Jewish sabbath.

The digruntled party members used this episode to call for a vote of no confidence in Rabin, a tactic that was really a pretext for a political expression of disappointment with Rabin generally. Rabin survived the vote but eventually ousted the Religious Party ministers who had voted against him for breaking coalition unity. This caused him to resign and call for new elections, which he lost.

At the time, the situation gave rise to the most unusual compliment ever paid to a jet fighter. "What a wonderful plane the F15 is," opposition politician Ezer Weizmann, now Begin's defense minister, said. "It can shoot down a government."