SEN. ORRIN HATCH elicited from Rear Adm. John Poindexter yesterday a statement that the decision to explore an opening to Iran 1) was the president's and 2) was the product of serious study and review. Evidently Mr. Hatch meant to be establishing Mr. Reagan's capacity for staying on top of policy in his own government. Actually he was establishing the president's responsibility for the basic flaw of the Iran-contra affair, the source from which all else flowed.

Of course, it was reasonable for the American government to be looking to establish some better relationship with Iran in time and also to explore any openings toward moderation that were possible. But the judgment made and the arrangements entered into on the basis of a reading of some of the most exploitative elements in Iran as "moderates" all but define the problem. It was thought that if these fake "moderates" were carefully cultivated, they could either (depending on your reading of the president's purpose) produce the hostages or restore a hostile Iran to a political and strategic situation consistent with the American interest.

At this point it should be evident that the narrower purpose, of dealing with certain elements in Tehran in order to get back the hostages, was quickly discredited. The few hostages who were released were quickly replaced by new Americans seized in Lebanon. That Adm. Poindexter destroyed the presidential finding authorizing such an exchange suggests that he came to understand the futility of this exercise, if he did not start with it.

The United States was not able to make a good test of the broader purpose of the Iran opening, to explore avenues for moderating Iranian policy. But a full-fledged test subsequently was made by France -- to which, by the way, Ayatollah Khomeini owed a great debt for its hospitality in his years of exile. As Flora Lewis usefully recalled on Monday in The New York Times, the French, seeking to "normalize" relations with Iran, kicked out another Iranian exile, a leading rival to the ayatollah, and settled a third of a billion dollars upon Iran in partial repayment of an old loan. The Iranians responded by giving refuge in their Paris embassy to an embassy translator (not a diplomat) wanted for questioning in some terrible bombings; this is the incident that triggered the current explosive crisis in French-Iranian relations.

In light of the centrality of the opening to Tehran, by the way, it is especially unfortunate that the congressional committees apparently do not intend publicly to question Michael Ledeen. As the first American to discuss an opening to Iran with the Israelis and the first to meet with a supposedly moderate Iranian, Manucher Ghorbanifar, Mr. Ledeen is in a unique position to inform Congress about the launching of the policy whose crash is absorbing its attentions day after day