ONE OF THE nightmare scenarios of the Iranian revolution has always been a plunge into chaos or civil conflict that ended the central authority of the state and precipitated a military coup, a Marxist guerrilla takeover, another or a deeper foreign invasion, an ethnic secession or something equally extreme. It is probably too early to say Iran now stands at that brink. If that scenario came, however, it would likely unreel from just the sort of blood bath that Iran has seen in the last few days. In quick succession, the government executed scores of people demonostrating in support of ousted president Abol Hassan Bani-Sadr, and Sunday night scores of government officials, including Ayatollah Khomeini's likeliest successor, fundamentalist leader Mohammed Beheshti, were killed in a single ghastly bomb explosion in Tehran.

What will happen as a result of this latest round of violence obviously cannot be known. The government, which had executed hundreds of other Iranians before it took after Mr. Bani-Sadr's supporters last week, would seem to retain the capacity to deploy its regular and irregular forces against perceived enemies of the revolution. Its taste for its enemies' blood will scarcely be diminished by the terror directed against its leaders Sunday night. At the same time, whichever individuals or groups set that explosion can hardly have intended that to be their last act in the Iranian struggle for power. As ugly as some scenes of Iran's revolution have been in the past, the worst may be yet to come.

Almost by reflex, various spokesmen of the Iranian revolution at once blamed the United States and, of course, "Zionism" for the bomb slaughter. One could say, in a patronizing way, that, well, Iran's Islamic fundamentalists are understandably upset and should be permitted their rhetorical excesses. We would say something else: the charge is a disgusting libel.