Washington's get-tough policy on the hostage crisis has turned Iranian "moderates" into hard-liners -- and could soon leave President Carter with a single, potentially dangerous option: to get still tougher.
This, as worried Tehran diplomats see it, could involve a series of escalating military actions or a renewed attempt to rescue the American captives , assuming the location of all of them can be discovered.
If Washington gets tougher, however, the reaction of Iran's Soviet neighbors is at best unpredictable.
With the active cooperation of the local governor and nary a squeak so far from Iran's "moderate" President Abolhassan Bani-Sadr, militant Muslim students riding a new tide of anti-American fervor said April 28 they had moved at least some of the former US Embassy hostages to the disused American consulate in Tabriz. That city is in Iran's northwest corner, only some 50 miles from the USSR.
Diplomats, by nature, do not like outlining scenarios for world wars that may never happen. Envoys in Tehran remain confident that neither Washington nor Moscow will consciously march into a confrontation over the Iranian crisis.
But their concern is that the crisis now has taken on a life of its own, and that particularly after the US attempt to rescue the hostages failed, internal political pressures in both Iran and the United States are making a negotiated resolution more difficult by the day.
The Americans are seen as increasingly unlikely to return to a route many Western diplomats have favored all along: to do nothing, or very little, and simply wait for what they see as essentially an internal Iranian crisis to sort itself out.
A restrained and lawyerly US Secretary of State Cyrus Vance has resigned. National Security Adviser Zbigniew Brzezinski is talking tough. Neither development is particularly reassuring to most Tehran diplomats, much less to the rapidly vanishing breed of "moderates" inside Iran.
The progressive hardening of Iran's moderates, meanwhile, seems likely to reinforce US hard-liners.
President Bani-Sadr, the French-educated economist on whom Mr. Carter once seemed to have placed all his negotiating bets, is sounding increasingly like Ayatollah Ruhollah Khomeini, whom the Americans have mistrusted from the start. So is Mr. Bani-Sadr's tight circle of Western-schooled aides, some of whom reportedly have tried to argue him out of hurrying to Iran's more hard-line Muslim clerics in the past.
So when Ayatollah Khomeini called for an international tribunal on "US crimes" on April 27 -- precisely the kind of forum viewed by diplomats as a potential, if hardly ideal, way of resolving the hostage crisis not too many months ago -- one Stanford-educated aide to Mr. Bani-Sadr commented privately:
"I can't exactly say the situation is hopeless. But I can't say this is a step toward negotiation, either. It is simply a step to show the dimensions of American crime. . . . The Americans, by imposing economic sanctions and attacking Iranian territory, have shown they are looking for hostility."
Mr. Bani-Sadr himself reportedly delayed a scheduled meeting with various noncommunist ambassadors April 28 for the third day running. Such a session could provide the first real indication of how seriously the aborted US rescue attempt has damaged the chances for a negotiated settlement of the long hostage ordeal.
Embarrassed yet again by the country's hard-line clerics, this time over his pledge to return the remains of Americans killed in the rescue attempt to the US government, Mr. Bani-Sadr meanwhile issued a statement few hard-liners could fault:
"It is obvious that the [American] aggressor does not change until there is a catalyst forcing a change. . .," the statement said in part.
Mr. Bani-Sadr's suggestion for such a catalyst was simple: a popular uprising in the United States to throw off "the evils of this devilish power through decisive and restless struggle."
President Bani-Sadr, not unlike his counterpart in the White House, has an increasingly militant constituency to deal with at home. It can be assumed he does not expect a second American Revolution, and that both he and President Carter would rather ease out of the hostage crisis than fight their way out of it.
But the most realistic scenario for a peaceful resolution of the crisis now seems to be some sort of "spy trial," likely to stir public controversy in the United States and unlikely to convene before June.
The Americans, strictly speaking, still have not turned to a full military option, that is, to an attack directed at Iran itself rather than merely at freeing the hostages.
But many diplomats here are concerned that such a military option now is more likely than a week ago. To act on it, they feel, could risk war, no matter how brief or limited. Though no one can predict the Soviet Union's response, that country's mere proximity to the arena of conflict is unsettling.
Ironically, a second rescue attempt is seen as potentially more complicated and more dangerous.
The hostages, their captors maintain, have been scattered to various locations around Iran. It remains unclear whether all the new sites will even be announced. The one site that has been mentioned clearly would be a very tricky target for another rescue mission.
Would the Soviets react if US forces try to rescue the captives from the Tabriz consulate, assuming that even would be feasible?
The answer lies inside the Kremlin. But one European diplomat, reflecting a growing consensus here and citing reports from his country's embassy in Moscow, argues a Soviet retaliation cannot be ruled out.
"Even on a brief rescue mission, when you get that close to Soviet territory in the current international climate, you are playing with fire," he said.
And in the event of prolonged military action in the area, he said, "I think the Soviets might well act on Article 6 of their  treaty with Iran."
That pact, allowing for intervention in the event of a threat to the Soviet Union through Iran, was abrogated unilaterally by Iran last year.
"But the Soviets," said the diplomat, "don't recognize that unilateral move. For them, the treaty is still in effect."