''Who will free me from this turbulent priest?'' cried Henry II to his nobles. His plea was answered by four knights who rode off to Canterbury, where, at twilight, they killed Thomas a Becket, the priest the king found so troublesome. In both history and literature, the murder of Becket has been told many times. It is amazing then that the White House would like us to forget its lessons.

Like Henry II, Ronald Reagan feigns shock at what his barons did in his behalf. But his desires were translated by obedient subordinates into actions. They understood the meaning of his constant entreaties to help the contras, his support of private fund raising in their behalf, his Chicken Little view of the Red Menace and his obsession with the Sandinistas. He was able to walk through a forest of Norths and Poindexters, McFarlanes and Caseys, and not see or hear anything.

The mysteries of Becket's murder have captivated historians and theatergoers for centuries. But they have been equaled by the mysteries of Washington. Here, in May 1986, the president told John Poindexter, then his national security adviser, ''Look, I don't want to pull out our support for the contras for any reason. This would be an unacceptable option. Isn't there something I could do unilaterally?'' The words are as loaded as any Henry II uttered to his knights. Yet Washington continues to look for the so-called smoking gun, and, having found none, either acquits the president of all responsibility or presses the search.

T. S. Eliot, who based his play ''Murder in the Cathedral'' on Becket and Henry II, would have found abundant material in the congressional investigation into the Iran-contra affair for yet another drama. Irony abounds, although it's wasted on the president's blunt men. Lt. Col. Oliver North, for instance, seems not to understand that when he was compelled to testify publicly he did more for his beloved contras than he ever did by secret and dishonest machinations.

A growing number of Americans -- although not a majority -- now support aid to the so-called Nicaraguan freedom fighters, according to various public-opinion polls. It turns out candor and honesty have an efficacy after all.

The ultimate irony, though, is the intent of the Iran-contra investigating committees to be legally meticulous. They sift through documents and transcripts in an archaeological fashion, looking for the one piece of evidence that would prove presidential complicity in the diversion of funds to the contras. All around loom temples of intent: the single-mindedness of the president when it came to the contras; a web of deceit when it came to informing Congress; repeated lies to the American people; and, in the end, the shredding of evidence. The scandal is only incidentally a criminal one. It is first and foremost one of premeditated policy.

But the charmless and cagey Poindexter gave Reagan away. Proving that at least some military men have politics after all, he testified that he kept the president ignorant of the diversion. His purpose was to offer Reagan the political advantage of deniability. ''I was convinced that the president would, in the end, think it was a good idea,'' Poindexter testified. ''But I did not want him to be associated with the idea.''

There we have it. The so-called smoking gun is not a document, not an order, but the ideology and mentality of Ronald Reagan transmitted to his staff. Here was a president who would, in the view of his subordinate, approve a possibly illegal and certainly dishonest plan to aid the contras. Here was a president who knew better than to ask for the details, who dared not pry, who would not ask who financed the contra resupply mission that brought about the Nicaraguan capture of Eugene Hasenfus -- who would, like a rich taxpayer, not approach the accountants to ask why no taxes were due. The results, the bottom line, were all that mattered to Reagan. How he got there seemed to be of no concern to him.

From Alexis de Tocqueville in the 19th century to the Japanese in this one, foreign observers have noted the importance of lawyers in American society. A joint congressional committee composed largely of lawyers has looked in vain for evidence of a crime. It seems not to know that while the Iran-contra affair might be a criminal conspiracy, it is foremost a political scandal.

Policy was communicated by ideology, not by memo; there was always a shared agreement on what must be done. Henry II's knights were dispatched on their evil errand with such an understanding and so were Ronald Reagan's. The king's wish was their command.