ABU DHABI, UNITED ARAB EMIRATES -- Despite two dramatic displays of military power in recent weeks, the U.S. Navy's deployment in the Persian Gulf has failed to convince a number of Arab leaders that the American military presence here will prevent what the Arab states fear most -- an Iranian victory in the land war against Iraq.

According to Arab officials and advisers to the governments on this side of the waterway, the inescapable concern controlling Arab attitudes toward the United States is Iran's enduring, belligerent presence and the potential threat that it will pose when the western fleets inevitably depart or contract.

Iran skillfully exploits these fears in diplomatic contacts with Arab leaders, according to Arab sources, while the Reagan administration, already in conflict with Congress over U.S. military involvement here, cannot guarantee the outcome of the war.

And, though U.S. military officials have been buoyed by the capabilities they have demonstrated against Iranian speedboats and mine-laying operations, navigation in the Persian Gulf remains as dangerous an enterprise as before the western fleets arrived, perhaps more so.

The inability of the U.S. and western navies to cope with dozens of attacks on unescorted merchant shipping since midsummer has raised questions about whether the United States can field "a coherent, forceful and consistent policy" in the region, as one official put it.

One key adviser to the Arab governments here suggested that firm U.S. military action -- such as the Sept. 21 attack on the mine layer Iran Ajr and Thursday's helicopter retaliation on Iranian gunboats -- will convince Arab leaders over time of an unstated U.S. commitment to blocking an Iranian victory in the broader war.

U.S. Defense Department officials say U.S. forces are here only to protect U.S.-flagged vessels, but they also speak increasingly of the U.S. mission to "contain the war," and such statements have further raised Arab expectations.

American policy in the region has little to offer on the larger issue of containing Iran or blunting the formidable Iranian thrusts against Iraq's borders.

"The whole issue is out of focus when one talks about accompanying or escorting ships," said one Arab adviser. "The issue is the war and how to end it."

U.S. assurances on how the war will turn out are limited to promises that the Reagan administration is doing what it can at the United Nations, where the 15-member Security Council adopted a cease-fire resolution in July but has delayed consideration of an arms embargo against Iran for noncompliance.

"I don't think the war is going to stop for any of this," said one Arab adviser who believes that Iran has been using diplomacy to buy time for its preparations for a major land offensive this fall and winter.

This official said Arab leaders consider the American approach to the gulf war to be piecemeal.

"The worry here is that there has been a {U.S. military} initiative, not a clear-cut, constant policy" for the region, the official said.

This official said some Arab leaders feel that a demonstration of U.S. "resolve" and "strength" through large naval deployments will fall far short of deterring Iran's religious-inspired vengeance on Iraq for starting the war in 1980.

American congressional delegations and diplomats have been "told quite clearly" that "a show of resolve and staying power" is not sufficient to deter Iran and "on the contrary is going to attract escalation," this official said.

Some Arab leaders have been privately pressing Washington to make a declarative policy statement that the United States will not allow Iran to win the war.

These leaders also would like President Reagan to elaborate on president Jimmy Carter's pledge of keeping the Persian Gulf an open waterway by adding a new promise to defend Arab states against Iranian aggression.

One official described as a "vicious circle" the constant U.S. pressure for more basing facilities in the region against an equally constant Arab pressure for greater U.S. commitment to Arab security.

Without a more explicit U.S. policy, some leaders of Arab states along the gulf will remain reluctant to openly assist the U.S. and western military presence or to endorse U.S. actions, such as the attack on the Iran Ajr and last week's helicopter assault on four Iranian gunboats, these officials said.

Arab officials, still deeply suspicious that the Iran-contra affair in the United States exposed Washington's obsession with Iran and an Israeli-inspired disregard for Arab security, have found fresh reasons for skepticism about the West:U.S. energy firms have continued to purchase large quantities of Iranian oil -- thus indirectly sustaining Iran's war effort. And the Reagan administration's commitment to pushing an arms sale package for Saudi Arabia through Congress has yet to clear the Senate. Britain, up until last month, was allowing Iran to operate a commercial arms purchasing office in London. West Germany has permitted a similiar facility to operate in Frankfurt. British officials also belatedly acknowledged that Iran successfully procured British-made industrial technology that has helped Iran become self-sufficient in the production of ammunition and artillery shells, which rain daily on Iraqi border cities.

The continuing reluctance of Arab leaders to embrace openly the U.S. presence in the gulf is posing ongoing logistical problems for the U.S. military, which has only a limited number of onshore facilities to support more than 24,000 sailors, marines and aviators aboard U.S. warships in the region.

The lack of onshore facilities has hampered U.S. capabilities, especially in projecting air power over U.S. naval forces patrolling the northern reaches of the waterway near Kuwait, according to western officials in the region.

U.S. commanders recently have resorted to such makeshift innovations as leasing offshore barges to store supplies and to base small antimine and antiguerrilla speedboats north of Qatar in the central gulf.

The Arab reaction to the U.S. and western naval deployments here is significant because it may be causing U.S. officials to focus on the contradictions of an American policy that was hastily drawn last spring in response to Kuwait's request to U.S. and Soviet officials for protection for its oil tanker fleet.

These contradictions were illustrated in remarks last week by Rear Adm. Harold J. Bernsen, commander of the 11-ship Middle East Task Force, which has immediate responsibility for U.S. convoy and mine-hunting operations in the gulf.

Speaking to pool reporters aboard the USS LaSalle last Sunday, Bernsen said, "Our presence in the gulf is designed to do a number of things. One of those things is to encourage the containment of the war."

This statement and similar ones have been widely noted by Arab leaders looking for some assurance that the United States will define containment as preventing an Iranian victory or subversion of its Arab neighbors.

According to a senior adviser to one of the rulers in the region, American officials have stated in private that "the Iranians should not be allowed to win the war."

These officials acknowledge that the dilemma for the Reagan administration in making such a commitment is that it must commit itself to preventing the fall of Iraq.

The likelihood that Congress and the American public will go along with the massive financial and military backing required to rescue Iraq in the event of a major Iranian breakthrough in the land war appears extremely remote. Yet this is the very commitment that Arab leaders are beginning to regard as essential to their long-term security, according to one senior Arab adviser.

When asked what commitment U.S. forces have to such countries as Saudi Arabia, Bernsen said the U.S. presence was helping to ensure stability.

"In other words, not a specific country, but a group pf countries -- the gulf states, the Arab states," he said.

But at another point in his conversation with the reporters, Bernsen said the role of U.S. forces was to "respond to threats against United States flag vessels, and that's the extent of my function out here -- militarily."