Lt. Col. Oliver L. North said yesterday his attempt to conceal that someone else paid for a security system at his Great Falls, Va., home was the "grossest misjudgment" of his life, but swore that he "never took a penny that didn't belong to me" from the Iran-contra funds.

North admitted he had cashed $2,440 in traveler's checks from a secret fund he maintained for the contras and other activities, but said the checks -- used to buy groceries, snow tires and leotards at a women's hosiery store -- represented reimbursements for "my own . . . paycheck money" that he used for expenses related to his work at the National Security Council.

In his second day of testimony, North was questioned closely about possible benefits he received from the network of Swiss bank accounts set up for the Iran-contra operations and earlier disclosures that private businessmen working with him attempted to provide financial assistance to his family.

In response, North delivered an impassioned defense of his personal integrity and said the security system was justified to protect his family from a threat made by a group headed by Palestinian terrorist Abu Nidal.

"I am glad to meet Abu Nidal on equal terms anywhere in the world . . . ," North told the congressional Iran-contra committees, "but I am not willing to have my wife and my four children meet Abu Nidal or his organization on his terms."

The former White House aide also denied knowing about a $200,000 death benefit account set up for his family by Albert A. Hakim, the business partner of retired Air Force major general Richard V. Secord, who assisted North in setting up the private Iran-contra network. North also said he was unaware that Hakim had prepared documents under which North would control $2 million in Iran-contra funds if both Hakim and Secord unexpectedly died.

North said Hakim did promise to provide financial assistance to North's family if North failed to return from his May 1986 trip to Tehran. With his approval, North's wife met in Philadelphia with a lawyer working with Hakim, he testified.

"There was no money mentioned," North said. "No account mentioned. No will mentioned. No arrangement. The meeting focused on how many children I had, their ages and a general description of my family."

North said he tried to get security protection from the government after the threat against him from Abu Nidal's organization shortly before he was to leave for Tehran in spring of 1986. He testified that he was told the government was not authorized to install such a system, while private contractors could not install one fast enough.

Concerned about his family, North said, he turned to Secord, who arranged for former CIA electronics specialist Glenn A. Robinette to install the system, which cost $13,900. At least $9,000 came from Iran-contra funds, according to earlier testimony.

"I think the government of the United States should have stepped up to it and didn't," North said. "Whether it's because of laws or regulations, I don't know."

Navy spokesman Lt. Cmdr. Bob Pritchard said yesterday that North was eligible to receive protection from the Naval Investigative Service (NIS) at the time of the Abu Nidal threat but that North did not request it. After a new threat against North's life last April, the NIS began providing security for him and his family.

North praised the NIS detail yesterday and suggested that his current protection came about because the new threat occurred after he returned to full-time duty in the Marine Corps. "The big difference was, this year, I was back with a band of brothers that has a long reputation for taking care of its own," North said.

North said that at the time of the Abu Nidal threat, he discussed his concerns about security with then-national security adviser Rear Adm. John M. Poindexter and an NSC aide, but nothing could be worked out. A White House spokesman said yesterday a preliminary search had turned up no documents referring to North's security issue.

North's home is under the jurisdiction of the Fairfax County police. Bill Coulter, a Fairfax police spokesman, said yesterday there was no record of a request for protection from North.

North said that when he did not get a bill for the security system, he concluded that Secord and Robinette decided "to make a gift out of" it.

North said he still isn't sure who paid for the system, but added "if it was Gen. Secord . . . thank you, Gen. Secord." Then in further defense of his actions, he said, "And . . . you guys {Congress} ought to write him a check because the government should have done it to begin with."

North said that after he was fired from the NSC, he "tried to paper over {the} whole thing by sending two phony documents . . . to Robinette," which he called "probably the grossest misjudgment I have made in my life."

North said that while at the NSC he got approval from then-CIA Director William J. Casey and others to set up a secret account of more than $150,000 to support contra activities and other secret NSC operations. The money came from traveler's checks supplied by the contras and cash provided by Secord.

North said Casey gave him a ledger to monitor the fund. "I kept a detailed account of every single penny that came into that account and that left that account," he said.

On occasions when the account was temporarily empty, North said, he used his personal funds and later reimbursed himself with the traveler's checks.

Early last November, he destroyed the ledger at Casey's urging, North said.