The Iranian crisis entered a new phase last week. Events made an indent for fissure between the government of the Ayatollah Khomeini and the mob holding Americans hostage in Tehran.

In consequence there opened an opportunigy for this country and its allies to mount pressure. Since President Carter seems to shrink from any show of force, the pressure has to be applied judiciously and slowly, so the true test of American resolution is the development of a far tougher energy policy at home.

The inner politics of Iran changed last Monday when the regine won overwhelming approval for its new Islamic constitution. Up to that point the Ayatollah Khomeini and his Revolutionary Council had an incentive for confrontation with the United States as a means of whipping up fervent support for the constitution. They were thus one-to-one with the students holding Ameriicans hostage at the embassy.

The students continue to seek confrontation. Hence their constant talk of trying, and even killing, the hostages. But the Revolutionary Council has to get back to the business of governing. Clashes with religious moderates all around the country demonstrate how tenuous is the control exercised by the government. So it will be all the more sensitive to actions from the outside that complicate the task of governing.

Like most oil countries, Iran is highly dependent upon traffic with the outside world. It has to sell its oil and import food, raw materials and such intermediate goods as plastics and chemicals. The welfare of thousands of familiies is directly bound up with foreign remittances and with payments to students abroad. By interfering with that traffic, the United States and its allies can tip the Revolutionary Council away from an anti-American stance and toward release of the hostages.

But pressure to drive a wedge between the council and the students has to be applied judiciously. For one thing, the Revolutionary Council cannot afford to be seen yielding to outside pressure. Neither can it divorce itself from the students in an abrupt way.

The trick in dealing with Iran now is to put handwriting on the wall. It is to intimate future discomfort on a grand scale unless the authorities seize the present opportunity to avoid the worst. In that way the members of the Revolutionary Council will have an incentive to take their distances from the students in an atmosphere conducive to the delicate task of arranging the liberation of the hostages.

The need for allied cooperation reinforces the dictates of internal Iranian politics. Without help from Japan and the European allies, the United States cannot stay the flow of goods or credits to Iran. We cannot even prevent Tehran from profiting from the American refusal to buy Iranian oil.

But the allies have important interests at stake in Iran. The Japanese and Europeans are far more dependent upon oil from that country than is the United States, So they are apt to take sanctions against Iran only behind a kind of camouflage.

For that purpose, probably the best instrument is the banking system. If banks deny credit, exporters to Iran will have to refuse orders in a way that amounts to economic isolation.

Developng such pressures, however, is necesariy slow work. A show of American staying power is thus a critizal element. The allies will not cooperate, nor will the Iranians be disposed to be reasonable, if they think American concern is only a flash in the pan occasioned by the plight of the hostages.

Since President Carter has virtually ruled out military pressure, the best alternative way to show seriousness is through an energy policy. This country has a pressing need for a policy that reduces dependence on foreign sources of oil. That means going far beyond the tax on oil company profiits and other measures that the administration now has before the Congress. It means either rationing, or a limitation on imports, or a major gasoline tax.

So far the administration has confined its efforts to pushing harder for measures already before the Congress. It can be argued -- and is, in the White House -- that the president will slip in public standiing if he asks for stronger measures from Congress and doesn't get them. But he will slip a lot farther if he doesn't have the measures in place, and shortages begin to make themselves felt later in the year. For if Carter does not push through the tough energy measures when Iran unifies the country, he will never get them through. A world of trouble later, in other words, can be avoided by a show of resolution now.