Iran's invasion of Iraq has touched off a fresh scare among the conservative Arab rulers of the Persian Gulf oil states and encouraged them to seek to placate Tehran.

As a result, Saudi Arabia and the smaller pro-Western states have grown less willing to cooperate openly with the United States just when they appear particularly in need of U.S. support.

The gulf states are showing new caution in backing Iraq despite their private hopes that the Iraqis crush Iran's invasion and halt the spread of its Islamic revolution, according to Arab diplomats and U.S. officials here.

The wariness of these nations, the United States' key friends in the gulf, also led them to move away quickly from U.S. suggestions that now is a good time for joint militarymaneuvers to demonstrate resolve to Iran. None of the gulf states wants to appear moving closer to the United States when confronted by the rising power of Tehran, which still views Washington as "the great Satan," Arab diplomats say.

"If Iran is going to emerge as the biggest power in the gulf, then the Saudis don't want to be on its bad side," said William Quandt, a Middle East specialist and former staff member of the National Security Council. "This is a very fickle period for the gulf states--survival is uppermost in their minds."

Since Iranian troops pushed into southeastern Iraq on July 13, carrying the war to Arab territory for the first time, the Saudis and other conservative states have avoided condemning the invasion. In a message Friday marking the end of the Moslem fasting month of Ramadan, Saudi King Fahd called for peace but did not mention Iran's thrust across the border.

This silence is noteworthy because the gulf states generally have backed Iraq for most of the war with statements of support and financial backing totaling at least $20 billion. These nations--Saudi Arabia, Kuwait, United Arab Emirates, Oman, Bahrain and Qatar--feared the religious revolution espoused by Iran's Ayatollah Ruhollah Khomeini, felt the need to support a fellow Arab nation against Persian Iran and were encouraged by Iraq's early victories.

The gulf states' new caution reflects a desire to leave open the possibility of making a deal with Iran to halt the fighting, using as bait the offer of billions of dollars of war reparations, sources said. There are also reports--which U.S. officials could neither confirm nor deny--that the gulf states have slowed their supply of aid to Baghdad.

"They have a commitment and a feeling of solidarity with Iraq," said one informed source. "But we haven't seen big convoys of trucks or flights of planes going over the border with help."

Iraqi President Saddam Hussein publicly has called for Arab solidarity in the war and has dispatched envoys seeking more aid from Arab nations. But while there has been no official Iraqi denunciation of the gulf states' new approach, one Iraqi here with diplomatic experience privately called the policy "appeasement" and said Iraq would feel betrayed if no new aid were forthcoming.

The gulf states' fears of offending Tehran quickly enveloped the suggestion that the gulf states hold joint military maneuvers with the United States. American officials said the offer, made July 16 in the unusual forum of an off-the-record State Department briefing for reporters, has found no takers.

"Nobody wants to alienate the ayatollah. This is a difficult time to do anything with America," one Arab diplomat commented.

One source said that the Saudis were "terribly offended" by the offer, saying, "If the United States is willing to offer such maneuvers, why didn't it communicate it privately?" The source suggested that the Saudis feared that Washington might be trying to use the Iranian-Iraqi conflict as an excuse for placing U.S. military bases in the region.

A U.S. official insisted that Arab reaction to the briefing had been "positive," adding, "The signal went to Iran that there is a line that Iranian ambitions cannot cross."

The official said Washington is not "pushing the idea of maneuvers." He stressed that the United States already has bolstered Saudi defenses with the sale of F15s and Airborne Warning and Control System (AWACS) reconnaissance planes and that Washingon had previously declared its readiness to consult with these states on their security.

But the official conceded that now is a bad time for such suggestions because Arab public opinion has been outraged by Israel's invasion of Lebanon and perceived U.S. support for it and because the Arab states know that U.S.-Iranian relations are "especially bad."

Another reason for some gulf states' lack of interest in maneuvers is their historic opposition to the introduction of troops of either superpower in the region.

"We hope the gulf states will close their ranks so as to prevent any form of foreign intervention," Kuwait's Acting Minister of State for Cabinet Affairs Abd Awadi said in an interview with a Kuwaiti newspaper in which he rebuffed the U.S. offer. "Getting involved in superpower rivalries is easy, but it is difficult to get out of it."

The conflict has posed a dilemma for the conservative gulf states ever since it broke out in September 1980, because a decisive victory by either Tehran or Baghdad would leave the winner without an equal rival as a power in the area. Iran and Iraq are by far the two most populous countries on the gulf, and the smaller monarchies historically have sought to preserve a balance of power between them.

For the moment, therefore, the apparent bogging down of the Iranian offensive suits the conservative gulf states perfectly, Arab and U.S. sources say. These states are able to bide their time and hope that both sides will tire of fighting and reach a settlement that leaves neither with an overwhelming advantage.

If Iran routs the Iraqi Army, however, then the gulf states would feel much less sanguine, the sources say, because the Iranians conceivably would be in a position to march next on either Kuwait or Saudi Arabia.

A U.S. official called chances of such a scenario "remote." If Iran did threaten to invade, the official said, the gulf states would look for support from fellow Arab nations, but the United States might be asked to provide support for air defenses.

The gulf states' caution about criticizing Iran's invasion contrasts with sharp condemnations by two other Arab moderates, Jordan and Egypt. Jordan has been Iraq's strongest ally in the war and it called up some reserves after the invasion. Egypt, an Arab outcast for making peace with Israel, has appreciated the opportunity to demonstrate its commitment to the Arab cause and quickly announced a new arms shipment to Iraq.

Arab diplomats noted that these two countries could afford to take a stronger stance than the gulf countries because, as one put it, "they're a lot farther away from Tehran."