Iran's bid to end the ''tanker war'' in the Persian Gulf has run into a so-far unmovable obstacle: Iraq. Generally, the momentum in the nearly four-year-old Iran-Iraq conflict now seems to have turned in Baghdad's favor.
Still, there has been no visible sign so far that Iran is ready for negotiated peace on Iraq's terms, nor, for that matter, that the conflict has become any more ''winnable'' by either side.
Since this spring, the rocketing of oil tankers in the Gulf has become Iraq's strongest card in a conflict that, on the ground, had tended to favor Iran so long as its critical oil revenue from Gulf exports was unhampered.
Iraq, with a relatively tiny Gulf coast, had seen its oil exports curtailed more seriously and earlier in the conflict than were Iran's. By attacking a Greek tanker loaded with Iranian oil Sunday, albeit with little apparent damage, Baghdad has in effect signaled that it has no intention of dealing away its trump card.
The move, if followed by further successful air strikes, would present Iran with three main counteroptions - the first two so far unsuccessful, and the third apparently meeting with hesitation in Tehran:
1. Iran could try to resume its own air attacks on tankers near the Gulf shorelines of Iraqi-allied Kuwait and Saudi Arabia. The idea would be to revive jitters, in those countries and in the outside world, of eventual widening of the Iran-Iraq war. As a result, Iran clearly hopes, even countries backing Iraq might try to lean on the Iraqis to halt their tanker strikes.
2. Tehran could take another stab at securing that aim by nonmilitary means. Tehran has already made a bid to do just that. The speaker of Iran's parliament, Hojatolislam Hashemi Rafsanjani, said at Friday prayers in Tehran 11 days ago that Iran would be ready to halt tanker strikes if Iraq did the same.
The comments were presumably aimed at two audiences: the United Nations, which had just brokered a limited cease-fire in tit-for-tat shelling of civilian areas; and Arab Gulf states like Saudi Arabia and Kuwait.
3. Iran could launch the major ground offensive for which it has long had nearly a half million frontier troops in place. (Iraq said Monday it would destroy Kharg Island, Iran's main oil terminal, if Iran mounted such an offensive, wire services reported.)
The first two options have their unsavory aspects for Tehran. After striking tankers near Saudi Arabia and Kuwait with impunity, Iran lost a warplane to Saudi jets in early June.
And in the political-diplomatic arena, the Saudis and Kuwaitis have given no sign of ''pressuring'' Baghdad to halt its own tanker strikes. If indeed there has been such an attempt - the Saudis deny this - the result has so far been failure.
Meanwhile, the delay in sending the Iranian ground troops on the offensive has coincided with reports from Tehran of possible disputes within the Iranian leadership over the move. Specifically, there has been speculation of dissent between Iran's regular Army command and the paramilitary Revolutionary Guards formed by Ayatollah Khomeini's regime after the ouster of the Shah.
Some Western diplomats suggest, further, that Tehran may be concerned over Iraq's major frontier buildup in anticipation of a massive Iranian ground thrust.
Besides, the ''tanker war'' has altered the rules of the Iran-Iraq conflict.
Before, Iran's periodic ground offensives provided a key weapon in a war of attrition that left oil-squeezed Iraq at an automatic disadvantage. Now, Iraq has shown an ability to impose limits on the Iranians' own oil-export revenue.
Iraq's decision to launch Sunday's tanker strike no doubt owed partly to the fact that, in a two-week lull on that front, Iran had managed largely to revive its oil loading at Kharg Island.
Still, a new Iranian ground thrust would be intended to short-circuit any sense in Baghdad that the tanker war might finally have brought the conflict with Iran into the homestretch and that, at the finish line, Baghdad would be the closest feasible facsimile of a winner.