The sale of American F-15 jet fighters to Saudi Arabia is a profoundly important symbol in Saudi minds of Washington's recognition that their country plays an essential role today in the well-being of the United States.

Conversations with top officials over the past four days leave no doubt about the depth of Saudi feeling on this issue. In their view, it is a matter that goes far beyond mere security considerations, although they make it clear that they legitimately do need a modern plane for the defense of the kingdom and its huge but vulnerable oil riches.

High-ranking Saudis, including Foreign Minister Saud Faisal and Oil Minister Ahmed Zaki Yamani, express a concern that Washington does not fully appreciate the significance of Saudi Arabia's willingness to produce oil far beyond its own immediate needs for revenue and to prop up the hard-pressed dollar.

Saudi Arabia is the United States' most important source of foreign oil. Nearly half the oil that the United States consumes is imported and this country probably supplied about 25 percent of the imports last year.

Moreover, Saudi Arabia today is practically alone among the world's major oil producers in defending the use of the dollar to determine oil prices, thus maintaining the American currency as the world's most widely traded one. A switch to other currencies would send the dollar reeling downward, with serious consequences for continuing international confidence in the American economy.

Were it not for Western and particularly American needs, Yamani and others say, Saudi Arabia would do better to leave its oil in the ground where its value is increasing far faster than the return on any other investment it might make with oil revenues.

The Saudis are by all appearances the most soft-spoken, reserved and pro-American of all the Arabs. They are also extremely reluctant to threaten any country, particularly the United States, to which they look for security, technology, expertise and, above all, friendship.

Thus, when Saudi officials begin speaking about the adverse effect the rejection of the F15 deal would have on their willingness to underwrite American oil and financial needs, it is clear that they are more upset than their relatively low-key words even suggest.

When Yamani said in an interview published in The Washington Post Tuesday that if the sale of the F15s is rejected, "We will have a feeling that you are not concerned with our security and don't appreciate our friendship," some Saudis were immediately worried about the political impact of the statement on American public opinion.

Yet, no high-ranking Saudi would disagree with Yamani's markedly mild warning that rejection of the plane deal would undoubtedly affect the outlook on American oil needs and the dollar's troubles. In fact, the same warning came through in a number of private conversations in far more explicit terms.

Even the Foreign Minister, Prince Saud, whose position in the royal family demands a more measured stance than Yamani's, was notably straight forward in his comments on how Saudi Arabia would feel about a rejection of the plane deal.

"There would be questioning undoubtedly and undoubtedly the effect would be a reevaluation in the assessment of what the extent of our relations with the United States should be," he said.

It is perhaps not fully understood in the United States that the Saudis, for all their billions of dollars and barrels of oil, still feel very weak and vulnerable in their new role as the world's undisputed fiancial superpower. "We may be rich in money," said one Saudi official, "but we have only 5 million people, no real means to defend ourselves and little of our own technology to develop. We are really a very small country."

As a result of this prevailing view in official circles, the Saudis are looking to the United States for all kinds of assistance, from meeting its security and technology needs to political support for their staunchly anti-Communist objectives.

Saudis are mystified why Washington would rebuke a country which provides so much that is mutually beneficial to the United States and which shares its views on all major issues but one, the Middle East. Even then, the Saudis' sharply anti-Israeli rhetoric is extremely mild by Middle East standards and their interest lies clearly in peace rather than war.

To Israeli contentions that Saudi Arabia could send the F15 to a war front, the Saudis reply that they will not even be able to fly the sophisticated jet until the 1980s, leaving ample time for Middle East efforts. They belittle the notion they might transfer it to another Arab country, pointing out that this is too complicated for wars that seem to last but a few days.

From the Saudi viewpoint, this is the year of decision on buying a jet for the next decade, a decision that is bound to have broad ramifications for their entire defense establishment. With the jet come radar systems, technicians, ground maintenance and weaponry.

If Congress refuses to sell the F15 to Saudi Arabia, the Saudis seem fully prepared to turn to France for the $3.5 billion deal. Such a move, they unhappily observe, would mean some cost to their friendship with the United States and inevitably their support for American interests.