What started as a battle for the succession in Iran has now flared into civil war. But neither one of the principal forces currently engaged seems able to win decisively, and it is a question whether the continuing battle will not eventually draw the two superpowers into the Iranian vortex.

The present ruler of Iran presents a standing invitation to a power struggle. Ayatollah Khomeini is 81, and in poor health. He follows political affairs at a distance, preferring to hold himself above the battle as a kind of ultimate arbiter. Inevitably there emerged rival contenders to take over from him in running the government.

Abol Hassan Bani-Sadr was one. Bani-Sadr was elected president of Iran in his own right with 75 percent of the vote. He developed links with the military by taking over direction of the war after Iraq attacked Iran last fall. As a Western-trained official concerned with making government work, he had the support of most middle-class Iranians. As an economist who tried to marry Marx with Islam, he appealed to the radical Moslems -- the so-called Mujaheddin-e-Khalq.

For all these reasons, however, Bani-Sadr had only fair relations with Ayatollah Khomeini, He was liked, not loved. His best bet, accordingly, was to wait until the ayatollah expired, and then mobilize the various groups in his camp. Indeed, in May, an interview with Bani-Sadr published by a Middle East journal was titled: "Bani-Sadr Waiting for Khomeini's Death."

The other leading contender was Ayatollah Mohammed Beheshti. He was in a markedly different position. An Islamic fundamentalist, he was the secretary general of the Islamic Republican Party. Through the IRP. he controlled Parliament. He was also able, as chief justice of the Supreme Court, to referee disagreements between Bani-Sadr and Parliament. Most important of all, as a religious figure in his own right, and the dominant figure of the religious party, he had the inside track with Ayatollah Khomeini, So the Beheshti interest was to settle the struggle before Khomeini died.

What in retrospect looks like a count-down against Bani-Sadr began more than a month ago. On May 28, Beheshti announced that Bani-Sadr had violated the constitution by blocking the appointment of a foreign minister, and with respect to some property matters. On June 6, Bani-Sadr's Tehran newspaper was closed. On June 10, a public protest called for the "execution of Bani-Sadr." On June 12, Ayatollah Khomeini dismissed Bani-Sadr as head of the armed forces. That night, Bani-Sadr fled to a hiding place somewhere inside Iran, leaving behind a "message to the Iranian people" that claimed that his enemies were taking over in a "coup d'etat." On June 20, Parliament voted to impeach him.

That day the radical Moslems of the Mujaheddin-e-Khalq staged a protest march on behalf of Bani-Sadr in Tehran and a dozen other cities. The Revolutionary Guards, or bully boys of the Islamic Republican Party, met them headon. Several days of brutal street fighting followed, and there was a wave of executions. Official sources announced about 60 people killed Unofficial reports from Tehran indicated a much higher toll, and an atmosphere of terror.

On Sunday, June 28, Beheshti and the top leaders of the IRP met at party headquarters to consolidate their victory. In a dispatch to his paper here in Paris, Eric Rouleau of the French journal Le Monde, who has excellent connections in Tehran, reported that the meeting was set to name a candidate to replace Bani-Sadr as president. It was also going to mobilize several lay parties of the left -- including the Communist Party, or Tudeh -- against the radical Moslems.

In the midst of that meeting, with Beheshti on the rostrum, a large bomb exploded. Beheshti and more than 70 members of the party hierarchy were killed. The bombing was clearly an inside job, and a good deal of evidence, including the survival of several radical members of the IRP, points to the Mujaheddin, or some other left-wing Islamic group as the instigators. What shapes up now is further strife between the Islamic fundamentalists, who had been headed by Beheshti, and the Islamic radicals, aligned with Bani-Sadr.

The ebb and flow of the struggle so far suggests that neither side can win on its own. Decisive power appears to rest with two groups that have so far stayed on the sidelines -- the Tudeh Party and the army, which seems to be protecting Bani-Sadr. The Tudeh Party is closely tied to Moscow. And the army? Will it move? Or will it, as so often in the past, wait for a sign from Washington?