If the influence of a nation is measured by its military power, economic strength and diplomatic credibility, the influence of the United States in the Middle East is declining.

As demonstrated in Lebanon, our military buildup is of little use in the specific flashpoints of the Middle East. Despite the vitality of our economic system, our exports to the region are falling and the stringencies imposed by the Gramm-Rudman-Hollings formula may force an untimely cutback in foreign aid. And for all the sincerity and hard work of American diplomats in the region, Arabs and Israelis alike question the ability of the United States today to pressure the parties into major concessions in the peace process.

I do not fully subscribe to Charles de Gaulle's dictum that "a state worthy of the name has no friends, only interests." The United States has many friends in the Middle East and a vast array of political and economic interests.

But after a three-week visit to five countries in the region, it is clear to me that both our interests and our friends are being hurt by an erosion in our influence and by a perception of the United States as a less than reliable partner.

In fact, these developments are accompanied by slackening attention to the complex problems of the Middle East in Washington. The sharp fall in oil prices, a rise in terrorism and a host of other foreign and domestic troubles distract us from a region where a diminished American presence is likely to lead to advances by both Soviet and radical fundamentalist forces.

There may not be much danger of an immediate outbreak of general war. Yet, continued drift in our interest and slippage in our influence point to an increasingly unstable situation where events rather than policies, accidents rather than strategies, take control.

In short, without a full-scale effort to promote a peaceful resolution of the Arab-Israeli conflict and a steadier approach to questions ranging from the proper response to Muammar Qaddafi to long-term development aid, we face a prolonged period of instability in this volatile region.

On the surface today, strategic American objectives are sound: continued Western access to oil, limits on Soviet activity, and the security of Israel and moderate Arab nations. But the perceptions of leaders in the Middle East suggest a loss of American influence and credibility in several areas:

The peace process. Our role in this critical arena often seems thankless. But while the unraveling of the most recent round of talks is due to several factors, including lack of Palestinian unity, many leaders believe the Reagan administration has not thrown its full weight behind a solution.

Israelis say we are unable to pressure moderate Arabs to move toward recognition of Israel; Arabs say we have moved so close to Israel in recent years that we cannot exert needed pressure there. "Shimon Peres is doing more to educate his people to the need for peace than the United States government is doing to educate its own," one high Arab official in the region commented during my tour.

Political support. Political support in the region is often expressed, unfortunately, in terms of arms sales.

Our credibility as the ultimate guarantor of the security of moderate Arab states has been sharply diminished by the failure of the administration to deliver on commitments to Jordan and Saudi Arabia. The shelving of arms sales to Jordan, a small, economically troubled country with potentially hostile neighbors, is seen as a humiliating defeat for King Hussein, weakening his hand in dealings with Syria and the PLO.

Massive quantities of arms are available, and it is not in our interest, nor in Israel's, to see moderate Arab countries turning to other sources, especially the Soviet Union, for these supplies and the training and support related to them.

Economic support. U.S. aid is absolutely critical in helping countries in the region to address social and economic problems of sometimes staggering dimensions.

For example, Egypt, with a population explosion of 1 million more people every nine months, faces severe economic pressures now compounded by forces beyond its control. Foreign exchange earnings are plummeting as oil revenues drop, Egyptians abroad earn less to send home and a growth of terrorism cuts tourism. Our AID programs in Egypt are making an impressive dent, buildings schools, basic sewage systems and rural electrification projects. But crucial help to countries such as Egypt and Jordan from the United States is bound to be less in a day of Gramm- Rudman cuts.

Terrorism. No one presumes to have quick answers to the scourge of terror. Yet deplorable as the attacks are, we must not let them distract us from broader policy goals that could ease tensions. Throughout the Mideast, leaders criticized the administration for elevating Qaddafi to a hero's pedestal by lavishing attention on him. Isolation of Qaddafi would come far more readily if the policy of confrontation in the Gulf of Sidra were accompanied by a more sustained focus on the region's political and economic problems.

There are other signs of a loss of influence in the sharp drop in our exports in the region and smaller numbers of young people coming to the United States to study. The presence of many U.S.-educated students has always been a major asset.

Not all developments are negative. The determination of King Hussein and Prime Minister Shimon Peres, along with the efforts of Assistant Secretary of State Richard Murphy, deserve recognition. The immediate results of their work may be limited, but may yet prove, with renewed commitment, to be productive.

Against great odds, President Hosni Mubarak is prodding democratization in Egypt with considerable success. The policy of the Israeli government toward the West Bank now is aimed at encouraging Palestinians to assume more control over their own affairs, to improve the quality of life in the absence of a broader settlement.

The fragility of that effort and the frustrations that seem to sabotage the best efforts were evident last month in the brutal assassination of a leading Palestinian moderate, Zafer al Masri, the mayor of Nablus.

Some voices in the United States suggest that we can shift our attention from the region, that there is no solution to Lebanese strife nor to the Iran- Iraq war, that Israel is strong enough, that our oil needs have dwindled. That is not my view, nor that of responsible individuals familiar with the Middle East. On the contrary, we need to redouble our efforts to find political and economic solutions to the deep and bitter divisions in the region. Does anyone seriously believe that we can allow conditions to deteriorate to the point of another full-scale Mideast war, that our allies do not need Gulf oil, that we can ignore the Iran-Iraq war?

Our stake in the Middle East is vital. Our national interest is clear. We have many options, but all must be aimed at reinvigorating our presence in the region and reviving the peace process. It is time to take stock and devote attention at the highest level to the Middle East. We need to meet the legitimate security needs of moderate Arab states and follow through by explaining all the reasons to the American people. We need to expand economic aid, both unilaterally and through international organizations. Finally, we must encourage peaceful initiatives, perhaps challenging Syria by communicating more freely and frequently with its leadership.

We cannot relax in our efforts to bring peace to the region. The Middle East will not become less relevant to our national interests because it is less hospitable to our influence.