Iran pledged today to keep open the vital Strait of Hormuz, which carries 40 percent of the noncommunist world's oil supply.

There was, nevertheless, evidence of increasing concern by Iran's neighbors along the Persian Gulf coast that the Tehran government might launch a desperation raid against the Arab states' oil fields.

The fears were fueled by continued warnings from Iran that the gulf states face retaliation if they help Iraq in the bitter, 10-day-old, undeclared war between the two nations.

The Iranian announcement through the office of Prime Minister Mohammed Ali Rajai, appeared to observers here to be a move to forestall any international action to keep the strait open.

The statement accused other nations of considering "interference in the region of the gulf" under the guise of keeping shipping moving through the 40-mile-wide strait that runs between Iran and Oman and carries oil from Kuwait, Saudia Arabia and other gulf states to the rest of the world.

Tehran said it is going to keep the strait open "in full view of its international obligations" and it added that it wants "to assure the international community that Iran shall not hesitate in any effort to keep this waterway open."

While the threat to close the strait was held over gulf oil producers and Western consumers, diplomatic sources here reported that Iran has "behaved with impeccable restraint" in not hampering shipping through the international waterway.

Iranian Navy gunboats have stopped hailing ships to demand their destinations, according to sources here, and some ships have sailed, for navigational purposes, through waters that Iran warned them to avoid. Nonetheless Iran let no one forget that it could stop traffic in the strait if it wanted to -- either by mining the waterway, harassing giant tankers with its speedy gunboats or using its shore-based long-range heavy artillery.

The Iranian Navy is considered to be the most powerful in the gulf and the military service least affected by interference from Iran's religious rulers. It was out of respect for the Navy's strength and the possibility of Iran's action that 30 ships, mostly big tankers, remained at anchor outside the strait today in the Gulf.

There was concern here and in other Gulf capitals that Iran would attack the strait or the Gulf states' oil fields to get back at those they think are favoring Iraq. Tehran radio has increased its focus on the Gulf nations in recent days, accusing the United Arab Emirates of harboring Iraqi Naval vessels and Kuwait of aiding Iraq. a

Kuwait has acknowledged that its hospitals are caring for some Iraqi wounded, but added that it would do the same for Iran.

"The area feels it is not possible to have an invasion from Iran, but it is possible to have an air strike," said one official who is well-informed on the opinions of leaders of the entire region.

"The situation in Iran is such," he continued, "that they would do it not to gain anything but to embarrass the world in this area. We can't discount it."

One analyst cited what he called "the apocalyptic view of events" of some officials in this area who fear that Iran "out of bravado or desperation will simply take out the Arabian oil.

"They are concerned that the Iranians are madmen," he added.

It is for this reason, officials in the area said, the Saudi Arabia requested the United States to send four advance radar command planes to the region. These planes, with radar that can "see" for about 250 miles, would operate over Saudi Arabia and the Gulf to give an early warning of any possible Iranian attack on the oil fileds.

"They are probably good," said one official, "in that they are entirely defensive in nature and show that at least someone else shares our views. Psychologically it has meaning, but by itself it has very little military significance without planes and antiaircraft defenses to act on the information they supply."

The air defense of this region are largely untested. While Bahrain, for instance, has no air force, Saudi Arabia has more than 171 combat aircraft and Kuwait has two squadrons of jet fighters that can be used as interceptors and are believed to be well trained for that job. Saudi Arabia reportedly has moved antiaircraft guns and Hawk ground-to-air missiles to the coastal areas of Dammam and Dhahran, just across the Gulf from Iran, to protect its vital oil fields.

Iran's Air Force, once the strongest in the region, was believed to have been decimated by purges and lack of maintenance and spare parts since the overthrow of the late shah 20 months ago, but is has shown surprising strength in the war with Iraq. The Iraqi Air Force, on the other hand, has been unable to keep Iranian gunboats from bottling up the disputed Shattal-Arab waterway.