The cycle of violence unleashed form the beginning of Iran's Islamic revolution has entered a critical phase. Many observers believe the deadly attack carried out last night against the ruling Islamic Republican Party headquarters is the first sign of a civil war, or at least bloodbaths.

The attackers aimed with surprising skill at the very nerve center of the government. At exactly 9:05 p.m., a chain of explosions that lasted less than a minute reduced to a pile of rubble the imposing building teeming with people in different departments of the Islamic Republican Party.

The attack came during a special meeting of the party's executive committee presided over by Ayatollah Mohammed Beheshti, the party leader. The meeting included provincial party leaders, several government members including Prime Minister Mohammed Ali Rajai, the central bank governor, some undersecretaries of state and about 50 legislators close to Ayatollah Ruhollah Khomeini, Iran's supreme leader.

If the bombing had been coordinated with an armed forces plot, the Islamic Republic would have faced a grave danger. During several hours, the country risked becoming rudderless. Its main leaders -- killed, wounded or caught off-guard by the dimensions of the catastrophe -- would not have been able to react promptly to an insurrection.

The strong man of the government, Beheshti, who virtually controlled the legislative, executive and judicial powers, had just died. Several members of the government had been killed or wounded. Nearly a third of the legislators, among them the most committed in parliament, had been buried under the rubble, living or not. Hojetoleslam Ali Akbar Hashemi Rafsanjani, the parliament speaker, had barely escaped death. For an unknown reason, he had unexpectedly left the conclave just minutes before the building collapsed.

The potential threat hanging over the government was taken seriously, at least by leaders of the Revolutionary Guards and Islamic Committees. Well before news of the attack had been announced to the nation, militiamen spread out in the middle of the night in the main streets and around strategic positions in Tehran. Official buildings were lighted. Pedestrians were frisked, questioned and held if their identification papers were not in order.

Rajai invited the people this morning to denounce any movement that seemed suspect. At the same time, he appealed to them to keep calm, but in vain. As soon as the radio reported the scope of the catastrophe, Tehran residents poured into the streets by the thousands to demonstrate against the Americans and their presumed partisans, the munafikin , or hypocrites who play both sides of the street.

By midday, no one had identified the guilty with precision. But according to rumors, suspicions focused in two directions: Forqan, an extreme rightist Moslem organization, and the Mujaheddin, just as Moslem but with Marxist ideas as well. Both were accused of playing the game, "consciously or not," of American imperialism.

At last night's meeting -- kept secret for security reasons -- the Islamic Republic's main actors were to make decisions on the future of the country in several areas.

On the schedule: Choice of a candidate for president of the republic, steps to end the terrorist strikes that had become more frequent in the last few days, the economic and financial situation and a proposed law on political parties.

On the last point, a consensus already had been achieved before the conclave. Several officials had said, as early as Friday, that several Islamic and non-Islamic groups would be legalized shortly. The communists of the Tudeh Party, a faction of the Marxist Fedayan that goes along with the Islamic majority and the Trotskyists, among others, were to benefit from the law, it was said. This was because they promised to respect the constitution and especially because they had not taken up arms against the republic.

During a long conversation 24 hours before his death last night, Hojatoleslam Mohammed Montazeri, close to Khomeini and a leader of the clergy's radical wing, declared: "To neutralize the counterrevolutionary plot fomented by the United States, we are resolved to favor creation of an anti-imperialist front, embrancing Moslems and non-Moslems, even if the non-Moslems have adopted communism."

At first reassured by opposition groups' inability to arouse mass demonstrations in favor of the dismissed president, Abol Hassan Bani-Sadr, the rulers were beginning by two days ago to get nervous about a "terrorist project" organized, according to them, by the Mujaheddin, the biggest and best armed party in the "counterrevolutionary coalition."

Several bomb attacks were reported Friday and Saturday in Tehran, Qom and Mashad. Hojatoleslam Sayed Ali Khamenei was almost killed Saturday by a booby-trapped tape recorder. Khomeini's representative in the Supreme Defense Council and member of the Islamic Republican Party's ruling "triumvirate," he was seriously wounded in the lungs and neck.

A main leader of the Revolutionary Guards ha disclosed one day earlier a confidential document reporting a secret meeting of the Mujaheddin. His own name, as well as those of Beheshti, Khamenei and parliament speaker Rafsanjani, wre on a list of 13 high-priority leaders to gun down. True or false, this document seemed to excite the man we were talking with. He though then that stronger repression would be absolutely necessary. After a two-day pause, executions resumed Sunday morning.

In his final interview, Montazeri spoke in terms similar to those of the Revolutionary Guards leader: "Executions will go on. We will be firm and expeditious, whatever the criticism against us abroad. World opinion should try to understand us. Iran is in a state of revolution and, in additon, is a country at war, besieged on all sides by allies of the United States who seek our downfall."