The guiding hand behind secret Iran-contra operations, Lt. Col. Oliver L. North testified yesterday, belonged to the late CIA Director William J. Casey. By North's account, Casey was effectively his personal case officer from 1984, when the secret contra supply operation was "almost drawn up" by Casey, until early last November, when Casey suggested that it was time to "get rid of things . . . clean things up."

North said Casey was fully informed about, supported and was "effusive" in praising the plan to divert funds from the Iran arms sales to the Nicaraguan rebels. Casey called the diversion scheme "the ultimate irony, the ultimate covert operation," North said, because it diverted money from Ayatollah Ruhollah Khomeini to the benefit of the contras. North said he informed Casey of the diversion in February 1986 before the first of three diversions of profits from arms sales to Iran.

Officials and sources who worked with Casey said yesterday that North's description could be true, since it is consistent with Casey's fierce anticommunism, his secretiveness as director and his willingness to circumvent the normal government bureaucracy. Several of these sources also noted that Casey, who died this May, is a convenient cover and scapegoat for North.

The other person North identified yesterday as intimately familiar with his work for the contras was Adm. Arthur S. Moreau Jr., who was assistant to the chairman of the Joints Chiefs of Staff from 1983 until October 1985. Moreau died of a heart attack last December.

North has acknowledged that he lied repeatedly -- to the Iranians, to Congress and others -- in what he deemed to be the higher national security interests of the United States and the need to achieve "plausible deniability" for the covert operations in which he was engaged.

Nonetheless, he has repeatedly insisted to the Iran-contra committees in two days of testimony that he is now telling the truth. Several of Casey's closest Central Intelligence Agency associates said yesterday they could neither confirm nor refute North's claims.

One former Casey associate said, "There was never any way to tell everything Bill was up to . . . not then {when he was CIA director}, not today and probably not tomorrow."

North credited Casey with a hand in many of his activities. For instance, North said, Casey not only suggested that he set up an "operational account" to handle cash expenditures to and for the contras, but actually provided the ledger in which, North said, he kept a record of every penny that went in and out.

This became the catchall fund of $175,000 for travel, payments to contra leaders and even, according to North, activities inside Nicaragua, which North ran from his third-floor office in the Old Executive Office Building. North said "money was mailed from this account to addresses in Caracas, San Jose, Tegucigalpa and San Salvador, among other places, to support activities inside Managua."

North insisted yesterday that the traveler's checks from this account that he personally cashed actually represented reimbursements of advances he personally contributed to the fund. The ledger he kept would verify that fact, North indicated, but he destroyed it at Casey's suggestion early last November, just a day or two after the secret Iran arms sales were exposed publicly.

North quoted Casey as telling him, "Get rid of things. Get rid of that book because that book has in it the names of everybody, the addresses of everybody. Just get rid of it, and clean things up."

"When he told me to do so," North testified yesterday of Casey, "I destroyed it . . . ."

North testified that Casey was also the personnel manager of the secret contra supply operation, recommending in 1984 that North enlist retired Air Force major general Richard V. Secord to run key aspects of the operation outside the government and beyond the oversight of congressional intelligence committees.

"Director Casey is the one who had suggested Gen. Secord to me as a person who had a background in covert operations, a man of integrity, a West Point graduate . . . a man who, by Director Casey's definition, got things done and who had been poorly treated" when he had retired from the Air Force.

Secord previously testified that he did not meet Casey until 1985, but at their first meeting, Casey said that he knew much about Secord's background and work. Yesterday Secord declined to comment on whether Casey had suggested him to head the private network.

In 1983 the CIA declined to give Secord a security clearance. Two sources yesterday questioned whether Casey would have recommended a person for such a sensitive position who did not have such a clearance and whom Casey had not met personally.

Casey also functioned as intelligence officer for North, according to the Marine officer's testimony. For example, Casey told North that the key Iranian middleman, Manucher Ghorbanifar, was "an Israeli agent." North said Casey warned him that his calls from his NSC {National Security Council} staff office to Central America were being intercepted by the KGB from a Cuban listening post. At another point Casey recommended that two contra arms brokers not be used because one might be transferring technology to Eastern Bloc countries and the other might have been involved in using U.S. economic aid funds to purchase arms, North testified.

Casey also provided legal advice, according to North. The director told him that the NSC staff was not covered by the prohibitions of the so-called Boland amendment that restricted government support to the contras. In November 1986, North said, Casey recommended that he obtain a lawyer to handle a possible civil suit from the financiers involved in the Iranian arms sales.

North described an intimate relationship with Casey, who shared everything from books to advice. They traveled together and even discussed expanding the covert network in the future.

"Director Casey and I talked at length on a variety of occasions about the use of those monies to support other operations besides the Nicaraguan operation," North testified yesterday, speaking of the millions in profits from arms sales to Iran, gifts from foreign governments and private donors in the United States. When Congress resumed contra funding as expected, North said, "it might be necessary at some point in the future to have something, as he would put it, to pull off the shelf and to help support other activities like that."