DUBAI, UNITED ARAB EMIRATES, SEPT. 8 -- A week of shipping attacks in the Persian Gulf and a missile assault on Kuwait have raised concerns here over whether a massive U.S. naval buildup in these waters can continue to help protect vital oil commerce and the security of America's Arab allies.

In advance of U.N. Secretary General Javier Perez de Cuellar's peace mission to Tehran and Baghdad this week, Arab and western diplomats in the region have expressed anxiety that the positive political impact of America's deployment in the gulf will erode as its efficacy is challenged by bedeviling realities in the war zone.

Reflecting on the most recent wave of attacks by Iranian gunboats against gulf shipping, one Arab official said of the U.S presence here: "What has it been for?"

As diplomatic efforts to end the seven-year-old war take on momentum with the U.N.-sponsored mission, the United States appears to many diplomatic sources in the region to be bogged down in an isolated and increasingly irrelevant military operation while the Soviet Union appears to have deftly maneuvered itself into a role as peace broker, able to keep its communication channels open to both sides.

Both Iranian and Iraqi diplomatic delegations are in Moscow this week pressing their case for a resolution to the conflict -- visits that dramatize the increasing importance the opposing parties attach to the Kremlin's role as mediator. {Details on Page A16.}

While these talks go on in Moscow, the United States is scrambling for mine-sweepers and pursuing a diplomatic agenda calling for an arms embargo of Iran.

Meanwhile, gulf diplomats and shipping sources said in interviews that Iran's tactics in its use of mine warfare, guerrilla attacks at sea against unescorted vessels and its first launchings of Chinese-made Silkworm missiles against Kuwaiti territory have left the powerful U.S. military command here without an effective response.

{Iraq, after a two-day lull in attacks in the gulf, said Tuesday that it had hit two "large naval targets" -- its term for tankers or cargo ships -- east of Iran's Kharg Island oil terminal, United Press International reported. The strikes could not be confirmed.}

Shipping officials point out that the week-long resurgence of the "tanker war" after a midsummer lull showed that the American, British and French task forces were all but irrelevant in a theater of battle where unescorted targets remain plentiful and land targets largely undefended against the Iranian missile threat.

One senior shipping executive assessing last week's lineup of oil tanker victims of Iranian gunboat attacks noted that many of them flew the flags of countries not able to provide naval escorts.

The United States and the other big powers "have left an awful lot of Third World countries vulnerable," he said.

The small percentage {less than 1 percent} of oil tankers that have hoisted the American flag, or the flags of the other large maritime powers "have got protection," this official said, adding, "They've got a big warship next to them. What do they care about the rest of the world?"

Even with the naval buildup here, the fact remains that almost all of the merchant shipping in the gulf steams without escort and will continue to provide Iran with a bountiful array of targets for its seaborne guerrilla strikes.

The Iranians demonstrated with their gunboat attack on the Kuwaiti-flag cargo ship Jebel Ali on Aug. 31 that despite the U.S. commitment to Kuwaiti vessels flying the American flag, the much larger fleet of Kuwaiti-flagged ships is still very much at risk.

As the long-term commitment of the American, British and French navies comes more into question, Arab concerns about having to come to grips with their determined and militarily resilient Persian neighbor dominate diplomatic discussion in the region.

Iran's leadership, playing on these fears, issued statements during the weekend reminding Kuwait and other Arab governments that U.S. military power eventually will recede here, leaving them to sort out their relations with the revolutionary Iranian regime.

One Arab government official in the region said that aside from the narrowly focused protection Kuwait's oil-tanker fleet has gotten from U.S. deployment, the Arab gulf states appear as much in jeopardy from Iranian attacks at sea and internal subversion at home as before the buildup.

Although not speaking for his government, the Arab official voiced the growing apprehension of Arab leaders that the United States -- having, by its presence, exacerbated the tensions between Iran and its Arab neighbors -- will leave the region either under congressional pressure or in the event that the futility of its escort service is established by repeated attacks against unescorted oil tankers and cargo vessels in coming months.

Reports reaching Arab capitals that the U.S. Navy already is unhappy about its limited escort role in a war zone swirling with violence have done little to bolster confidence in a long-term commitment.

The options for a U.S. policy committed to keeping a large military force here are complicated by the scale of military forces required for even the limited mission the United States has initially staked out.

The armada of more than 30 U.S. warships has strained the modest logistical and support facilities the United States maintains in the region. The massive naval redeployment has also drawn down U.S. and North Atlantic Treaty Organization forces in other regions, such as the North Atlantic, where some Scandinavian countries are reported to feel that allied fleets have been stretched to the limits of adequate protection against the Soviet Navy there.

The missile attack against Kuwait dramatically demonstrated that the United States has little choice other than escalation to come to the rescue of any Arab ally whose territory is directly threatened by Iran.

Nowhere is the risk of escalation more worrisome than in Kuwait, where western and Arab officials are asking themselves this week who would respond if Iranian missiles were to fall on residential or industrial areas in the small emirate, as they have fallen in the past on Baghdad, Basra and other cities in neighboring Iraq.

The United States has made clear that it will bomb Iran's Silkworm missile sites overlooking the Strait of Hormuz if Iran uses them to threaten any U.S.-escorted convoy. But it has not made clear that it would respond if Iran uses its missiles in the northern gulf against Kuwaiti territory.