TWO facts complicate the role of the United States in the Gulf, and are among the elements in understanding the muted US reaction to the latest Iranian attack on a US vessel. Fact 1 is that there are 1,500 miles of mutual frontier between Iran and the Soviet Union.
Fact 2 is that Israel supports Iran and is probably still sending military spare parts to Iran despite US pressure to cease and desist; Israel does its best to influence US policy in the Gulf away from a clear association with the Arab cause.
The common frontier with the Soviets means that no US economic boycott of Iran could be decisive without the consent and collaboration of the USSR.
Israel's support for Iran drags back on US military collaboration with the Arabs against Iran. The pro-Israel lobby in Washington is still resisting the latest administration program for the military resupply of Saudi Arabia.
It would be easier for the US to decide upon and execute a strong and aggressive policy against Iran, were these two factors absent from the equation.
The US wants a speedy end to the Iran-Iraq war, with Iraq intact and Iran restrained and contained.
The US could achieve that state of affairs almost single-handedly by an economic boycott of Iran - if Iran did not have a common frontier with Russia, and if Israel was not giving Iran all possible help.
Iran is peculiarly subject to an economic boycott. Its foreign earnings come almost entirely from oil. Ninety-six percent of its exports are crude oil and oil products. Without the export of oil, it could not buy the weapons and ammunition it needs to maintain its war with Iraq.
Its oil now goes to the outside world almost entirely through the Gulf. Its main pipelines feed down to the Gulf at Abadan and out into the Gulf at several export pumping stations, of which Karg Island is the most used.
But there is a northern end to the pipeline at Resht, on the Caspian Sea. Tankers could take any desired quantity of Iranian oil from Resht to Baku, where it could go into the Soviet pipeline system.
Also, there is a rail connection.
Thus, the Soviets could, if they chose to do so, nullify a US-imposed blockade of Iran's oil. The blockade must have Soviet support to be effective. So far, Washington has been reluctant to discuss the possibility of joint action, although Moscow has invited mutual talks on the subject.
The result is that Washington falls back on what amounts to a half policy. It is protecting the export of Arab oil through the Gulf while allowing Iraq to continue to harass the flow of oil from Iran. This helps the Arabs in getting their oil to market by quite a lot, but puts relatively little restraint on the flow from Iran.
US intervention in the Gulf will not make a decisive difference in Iran's ability to wage war unless or until it does virtually close off the outflow of Iran's oil.
Meanwhile, the US ability to get full support from the Gulf Arab states, meaning primarily Kuwait and Saudi Arabia, is restrained by Israel's opposition to any supply of weapons to any Arab country. One US expert on the Middle East says that Israel ``has made it more expensive'' for the US to tilt toward Iraq. Had Israel permitted the supply of all the weapons Kuwait and the Saudis requested, ``the US would not now have 41 warships in the Gulf - with more on the way,'' he said.
Another angle is that in the absence of Israeli opposition, the US could have sold Iraq the sophisticated weapons that would have made it possible for the Iraqis to penetrate Iranian air defenses. In that case, they would not have felt the need to aim at the ``easy targets'' in the Gulf.
The main long-term purpose of US intervention is to save Iraq. It is getting to be more expensive than would have been the case if Washington had first gained the collaboration of both the Soviets and Israel.