The person who probably would give the most revealing testimony about the Iran-contra operation, if he were alive, would be CIA Director William J. Casey. He operated a secret government-within-the-government, which bypassed the traditional structure of checks and balances. This has been the most important finding of the investigation.

We described Casey in 1983 as "a loner who operates out of his hat; who lives in a continuous state of crisis; whose mind is encased in a Republican hard shell; who talks of Soviet-American relations in terms of 'showdown.' "

It was his style to withhold information from anyone who might be unsympathetic toward his goals. In fact, he reported only the bare bones of sensitive matters to his CIA subordinates. Thus he routinely short-circuited the system that was supposed to alert the Oval Office and Congress to any dubious schemes or operations. Intimates say he did not look upon himself as above the law, but constantly looked for loopholes that would allow him to evade the law.

The CIA's covert operations, for example, are restricted by law. No longer may the CIA sponsor coups and carry out assassinations around the world. So Casey simply recruited outside organizations to do the dirty work that the CIA is now prohibited from doing.

No one believes that Casey formed a separate, rogue government-within-the-government to do his bidding. Rather, they say, he operated through an informal, underground clique of hard-liners who were strategically placed throughout the government. They shared the same conspiratorial view of the world, the same combative attitude. They believed the United States is losing the world power struggle because liberal policy-makers have developed a schoolboy's crush on radicals.

Marine Lt. Col. Oliver L. North was a pivotal member of this unofficial, unorganized underground. We described his relationship with the CIA director last January. "North and Casey huddled frequently to discuss details of the Iran-contra operation. They left no memos or notes of their conversations . . . . Sensitive details were never discussed at meetings where anyone they distrusted was present."

In the same report, we stated that the Iran-contra conspirators "not only withheld from {President Reagan} information that might have embarrassed him, but intercepted documents that might have tipped him off."

That's why the president could say truthfully, as he did to us earlier this month, that he not only hadn't been told about the illegal diversion of arms profits to aid the contras, but that he was still trying to find out who raised the price. The U.S. government was paid the full market price for the arms; the president wondered who had overcharged Iran.

We can report it was the Israelis, with the connivance of Casey. As far back as April 1986, we reported that the first arms shipments were delivered by Israel "with the tacit approval of the CIA." Then the White House decided to ship the arms directly to Iran, we wrote, "instead of going through Israel."