THE IRANIAN revolutionary government fired the head of its national oil company last week. It seems that, ideologically speaking, he was insufficiently pure. Technical competence evidently did not enter into the choice of his successor. The level of Iranian oil exports continues to decline. If they were to drop off suddenly, as they did last December, the impact on every industrial economy would be immediate.

Here in Washington, the White House is preoccupied with the energy legislation now moving through Congress. That legislation is designed to set out strategies for the next two decades. But what if there were another abrupt disruption? Unfortunately, it could happen again at any moment.

Any national response to a future shortage would be severely hampered by the weight of all the suspicions and confusions arising from the last one. There is no consensus among Americans as to what really lay behind the gasoline lines last spring. The White House and the Energy Department have done remarkably little to provide clear and consistent explanations. The angry accusations and retorts continue. The Carter administration appears not to understand fully the crippling effects that these unresolved quarrels will have on any attempt to meet another crisis.

Last spring President Carter directed the Energy Department to conduct an investigation. The department published a first report in late July. As a tentative and interim assessment, it was a respectable effort.But that was 10 weeks ago. That report raised a number of serious questions that require answers. Some of the federal oil statistics have been substantially revised since early summer, and the department's current figures are not entirely consistent with the explanations that it offered in July.No doubt this investigation has been delayed by the change of command in the department. But the present secretary of energy, Charles W. Duncan, has no more pressing responsibility than to explain to the country precisely what went askew early this year in the gigantic and intricate oil-distribution system.

In the broadest terms, the cause was clearly the Iranian revolution. It arrived at a moment when the American oil industry had drawn its inventories low and when the country's demand for oil and gasoline was rising strongly. But the details of these events remain obscure, not least because of the conflicts among the government's own figures and its own explanations. Until the history of the spring gasoline shortage is better established, there is small chance of a rational and competent reaction to the next shortage.