The Iran-contra affair, now part of the primary text of American history, exposed the workings of two governments, one operating secretly, the other publicly. As Sen. William S. Cohen (R-Maine) aptly put it last summer, it is "a tale of two governments, one elected, the other procured."

It also exposed another kind of political story: of two Republican parties, one negative and narrow, the other positive and forward-looking. One resides in the House, where the permanent minority seems daily to grow more negative and obstructionist, as in its present threat to walk out if Soviet leader Mikhail Gorbachev addresses a joint meeting of Congress next month. The other operates in the Senate, where members have consistently demonstrated their capacity for national leadership during the Reagan years.

Ironically, both sides of these political equations have been illuminated by the workings of the congressional committees investigating the Iran-contra scandal.

Thanks to the committees and their admirable final report, the story of how two conflicting governments produced a historic political scandal during the Reagan presidency are clearly laid out for all to see. For years to come, Americans will be able to turn to that report and grasp instantly the essence of this complicated story of deceit and contempt for law. An example is the committees' description of the secret network, which was run directly out of the White House by Lt. Col. Oliver L. North and arranged for sale of U.S. arms to Iran and diversion of profits to Nicaraguan contras:

"The enterprise, functioning largely at North's direction, had its own airplanes, pilots, airfield, operatives, ship, secure communications devices and secret Swiss bank accounts. For 16 months, it served as the secret arm of the NSC {National Security Council} staff, carrying out with private and nonappropriated money, and without the accountability or restrictions imposed by law on the CIA, a covert contra-aid program that Congress thought it had prohibited."

So, too, the public can ponder divisions within Republican ranks by turning to the remarkable minority report filed by all of the party's House committee members and two of its five senators on the corresponding panel.

This report makes the preposterous claim that the Iran-contra affair represented nothing more than "mistakes in judgment." As for the documented record of lies, destruction of evidence, obstruction of justice and implementation of a cover-up, why, that's all nonsense, evidence of how egregiously the majority reached its "hysterical conclusions." In the view of this minority, "there was no constitutional crisis, no systematic disrespect for 'the rule of law,' no grand conspiracy and no administration dishonesty or cover-up."

For months, this minority accused Iran-contra congressional critics of harming national interests by failing to keep secrets and leaking classified information to reporters. Then the group's conclusions were leaked to the media while the committees' final report, including the minority version, still bore an official government security classification -- a fact that prompted another Republican, Sen. Warren B. Rudman (N.H.), to observe wryly that such a leak of the minority report was "rather ironic considering . . . those who leaked it."

Rudman, who had been a model of an independent, aggressive, fair-minded investigator during the hearings, exhibited those traits again Wednesday. "I am a Republican, and I am a loyal Republican," he said as the committees' report was released. "But I think the minority evidently believes that Republicans somehow don't want the truth laid out. My Republican constituents want the truth laid out.

"I have looked at that {minority} report carefully, and I'm regretful to say that I'm reminded of Adlai Stevenson's great remark about the press: 'This particular report is one in which the editors separated the wheat from the chaff, and unfortunately it printed the chaff.' It is a pathetic report . . . . To refer to this report of this majority of this committee as hysterical is, frankly, uncalled for."

To the everlasting credit of the Republican Party, the behavior of Rudman and the majority of the GOP Senate committee members differed markedly from their House GOP counterparts. They put the pursuit of truth above partisan political gain. They, their party and their country were the beneficiaries.