Brussels — For the first time, the Gulf war has spilled into Saudi Arabian waters with Wednesday's bombing of a Saudi oil tanker near the port of Ras Tanura, a major export facility.
If the attack was carried out by Iran, it would clearly demonstrate Iran's recent determination to disrupt oil traffic in the Gulf.
Iran is believed to be responsible for the bombing of two Kuwaiti supertankers earlier this week.
The Iraqis, for their part, have apparently been successful in their attempts to disrupt Iranian oil exports. After Sunday's destruction of two other tankers - apparently by Iraq - near Iran's main oil terminal on Kharg Island, several shipping and oil companies have decided to keep their tankers away from Iranian ports.
In an apparent victory for Iran, Lloyd's of London decided Wednesday to add Kuwaiti ports to a ''high-risk zone'' in the Gulf. Special insurance rates that already apply to Kharg Island now apply to ships going to Kuwait, thus jeopardizing the nation's oil exports. Iran would consider this a victory because it has pledged that the ''Gulf will be safe for everybody or nobody.''
The recent escalation in the war has not appeared to soften Iran's stance toward Iraq. On Tuesday evening a Tehran radio commentator repeated that the war would not end before the ''Iraqi aggressors'' were punished.
On Wednesday, after a meeting of Iran's Supreme Defense Council, the speaker of the parliament, Hashemi Rafsanjani, said, ''The US, France, and Iraq were plotting to make the Gulf insecure.''
Mr. Rafsanjani added that Iranian fighters would ''welcome a direct confrontation with the United States.'' But he did not confirm or deny the allegations that Iran had bombed the two Kuwaiti tankers.
As he emerged from the council meeting, Rafsanjani added that the council had adopted measures ''to face the new developments in the Gulf area.'' He did not elaborate on any plans.
Asked by an Iranian journalist whether the US might intervene militarily in the Gulf, he said, ''That would be crazy, but it shouldn't be ruled out.''
President Reagan has vowed repeatedly that the US will not allow shipping out of the Gulf to be blocked.
Iranian officials have often said the Islamic republic ''would react'' to the disruption of its oil exports. But Foreign Minister Ali Akbar Vellayati recently said Iran would not blockade the Strait of Hormuz ''unless all its exports were cut.''
The Iraqi Ministry of Information confirmed on Monday that Iraqi Super Etendard jets had attacked two small oil tankers, the Greek-registry Esperanza and the Iranian Tabriz.
The Iraqi communique triggered the sharp rise in insurance rates for ships heading for Iranian ports.
''A ton of Iranian oil,'' a Western oil company executive explained on Tuesday, ''now costs $10 more than a ton of North Sea oil.''
A shipping agent adds: ''There is a financial and human problem. More and more sailors refuse to go to Kharg Island.''
Japanese seamen's unions have asked their members to refuse to go to Iranian ports.
The long-term consequences of this disruption are difficult to assess because the Iranian Central Bank has announced it is willing to insure ships going to Kharg at the previous rate. The bank has even transferred several million dollars to an account in London to show it is able to insure any subscribing shipowner whose tanker might be destroyed while loading at an Iranian oil terminal.
It is not known whether this Iranian proposal has had any success. Even if Iran's exports were totally cut, Western financial experts say Iran could survive financially for several weeks. The Iranian Central Bank is said to have about $8 billion in reserve.
In recent weeks the Iranians apparently had improved trade relations with their neighbors on the south shore of the Gulf, namely Saudi Arabia, the United Arab Emirates, and Kuwait, all of whom support Iraq in the war. Iranian diplomats tried to convince their Arab counterparts that Iraq's extensive use of Super Etendards against oil tankers was the main cause of insecurity in the Gulf.
Arab rulers were said to welcome the assurance that Iran did not intend to destabilize their regimes. If confirmed, the Iranian attack on the two Kuwaiti tankers would mean the end of Iran's hopes of persuading Arab rulers to withdraw their support for Iraq. Iranian leaders might also have concluded that events in the Gulf have progressed beyond the point of political solution.
(Middle East analyst William Quandt of the Brookings Institution said Wednesday's attack on the Yanbu Pride ''would be a step up the escalation ladder. The Saudis may now have to decide whether to defend themselves, possibly with American help. But Iran doesn't have an overwhelmingly strong Air Force. Iran can't shut down Saudi production.''
(Referring to the possibility of US involvement, Quandt said, ''Although it would be a difficult political decision, in extreme circumstances there are plenty of ways to defend the Saudi terminals. It would be intolerable to the West to have the terminals undefended.'')