DUBAI, UNITED ARAB EMIRATES -- The Soviet Union, which has made significant diplomatic inroads in the Arab world over the past two years, is beginning to come under pressure from Arab leaders who are seeking Moscow's active assistance to end the Iran-Iraq war.

Concern in Arab capitals that Moscow, along with Peking, has slowed the pace of a U.S.-backed drive in the United Nations to enforce July's Security Council cease-fire resolution has put Soviet envoys increasingly on the defensive, according to western and Arab diplomats in the region.

"The tone is changing" toward the Soviet Union, said a senior western diplomat. "The Soviet diplomats in the region feel quite deeply that they are under suspicion."

These concerns have intensified as the violence from the "tanker war" in the Persian Gulf has threatened the Arabs and forced reluctant leaders in Saudi Arabia, Bahrain and Kuwait to take a harder line toward Iran.

In addition, the recent Soviet-Iranian discussions on improving trade ties and establishing rail and energy pipeline links between the two countries, have added to fears that Moscow is taking advantage of tensions in the gulf to position itself -- at the expense of peace initiatives -- to lay the groundwork for a long-term relationship with Iran.

"The prize is Iran," another senior western official said, when asked about the uppermost strategic objectives of the United States and the Soviet Union in the region.

This perspective does not ignore U.S. and Soviet efforts to build and strengthen their relations with Arab states in the region, but it does demonstrate the overlapping strategic interests that the superpowers are pursuing.

Concern over Soviet-Iranian relations, in part, led Kuwait to send its oil minister, Ali Khalifa Sabah, to Moscow earlier this month, according to a western diplomat.

"The rapprochement between the Soviets and the Iranians makes the Kuwaitis very nervous at all levels," the diplomat said, "and there was a lot more to the discussions than a simple oil deal."

The overlay of superpower competition in the gulf could become sharper after Soviet leader Mikhail Gorbachev's refusal last week to set a date for a summit with President Reagan.

A number of analysts here had predicted that the high-profile American military presence in the gulf would erode last summer's consensus among members of the U.N. Security Council to undertake a major diplomatic drive to end the war.

Many of these analysts see Moscow's broadcasting of almost daily criticism of the U.S. military deployment to the region as a sign that the Soviets have pulled back to let the Reagan administration's high-risk military deployment run its course.

On Saturday, Gorbachev said the cooperation between the United States and the Soviet Union to bring peace through the United Nations "is now called into question," because the United States is acting "as it did of old."

The Soviets have defined their gulf policy as everything the American policy is not.

The Soviets have maintained a low-profile military presence with a single frigate and a half-dozen mine sweepers and supply ships, while the American fleet is approaching 40 ships and now includes seaborne forts on barges anchored in the waterway.

The Soviets have called for restraint by both Iran and Iraq in the tanker war, whereas the U.S. military has targeted Iranian aggression against neutral shipping and has tacitly defended Iraq's bombing of tankers carrying Iranian oil in Iran's "exclusion" zone.

The Soviets have called for a withdrawal of foreign military fleets and a diplomatic solution, whereas Washington has emphasized the need for an arms embargo against Iran.

But some western and Arab officials in the gulf believe that an escalation of tensions, fueled by the recent missile attacks on Kuwait and U.S. Navy clashes with Iranian gunboats and mine-laying vessels, inevitably will force Moscow to commit itself to a course of action to end the war.

Such a course could require Soviet pressure on Tehran if Moscow hopes to keep the good relations it has established with a number of Arab states, these officials say.

As tensions in the gulf have increased, Iran has played a "Soviet card" against the Reagan administration, whose senior officials speak as often about the threat of growing Soviet influence in the gulf as they do about the Iranian threat to its neighbors.

It is such ambivalence at the core of U.S. policy-making in the region, many officials say they believe, that led the Reagan administration to secretly sell arms to Iran in 1985 and 1986.

The Soviet interest in stronger relations with the Arab states has been apparent across the range of Middle East issues. The Kremlin has won support for its efforts to convene an international peace conference on the Arab-Israeli dispute and successful brokering of the unity drive last spring in the Palestine Liberation Organization.

In the gulf, as elsewhere in the Middle East, Soviet policy-makers have managed to straddle the fence when their policy objectives collided.

For example, the Soviets managed to back PLO unity under Yasser Arafat without irreparably damaging their relations with Syria, where President Hafez Assad is sworn to undermine Arafat's control over the Palestinian movement.

But the policy conflict for the Soviets is much sharper in the gulf region, where relations with Iran must survive Tehran's deep opposition to the Soviet occupation of Afghanistan and repression of the Islamic movement there.

Even more, Moscow plays the delicate game of arms supplier to both the Iraqi and Iranian war efforts.

This is perhaps the greatest conflict in Soviet regional policy. One senior western diplomat said, "What we wonder about is why the Iranians get so upset about the United States protecting the {Arab} nonbelligerents' oil and say not a damned word about the Soviet Union delivering boatloads of arms to their enemy.

"It's hypocritical, and we find it hard to explain."

For the future, western analysts predict that the Soviets will find it more and more difficult to avoid committing themselves in this increasingly volatile region.

But Gorbachev, in additional remarks yesterday carried by the Soviet news agency Tass, showed a continuing deftness in doing so.

He showed Moscow's interest in strong relations with the Arabs by condemning Thursday's missile attack on Kuwait's sea island oil terminal, while his ministers continue to negotiate better relations with Iran.

"The Soviet Union has more than once declared its negative view of such actions, regardless of who commits them," he said.

Without referring to Iran, the Soviet leader added, "Attempts to draw third countries in the Persian Gulf into the conflict are inadmissible, no matter who makes them."