The late CIA Director William Casey tried to discredit a congressional staffer who had met with an official of Nicaragua's leftist government, a former House member said Monday.

Former Rep. Michael Barnes, D-Md., gave the testimony at Oliver North's Iran-Contra trial while answering defense questions about Victor Johnson, staff director of the Foreign Affairs subcommittee on Western Hemisphere affairs that Barnes chaired.Johnson at the time was assisting Barnes in pressing the Reagan administration to respond to press reports that North was soliciting contributions and providing tactical advice to the Contra rebels in Nicaragua.

Under cross-examination by North lawyer Brendan Sullivan, Barnes said Casey requested a meeting in the fall of 1985 in which the CIA director said the spy agency had intercepted a conversation of a Nicaraguan official.

The other party in the conversation was Johnson. Casey died in 1987.

Barnes said Casey quoted Johnson as telling the Nicaraguan official that if Nicaragua improved human rights and took other steps, those actions would help members of Congress who were trying to reject aid to the Contras.

"I found the allegations he made to be basically frivolous," said Barnes. "He didn't allege that members of my staff" were passing classified information to the Nicaraguan government.

"I told him in my judgment, based on what he told me," that what Johnson had done "was perfectly appropriate," said Barnes.

Earlier Monday, Barnes testified that then-national security adviser Robert McFarlane seemed "very nervous" about congressional inquries over North's activities.

Barnes described how McFarlane in a 1985 meeting offered to let him examine National Security Council documents pertaining to the Nicaraguan Contra rebels, but that McFarlane refused to let congressional staffers see them.

The meeting in McFarlane's office occurred after he had denied in a Sept. 12, 1985 letter to Barnes that National Security Council staffers were engaged in fund-raising assistance and offering tactical advice to the Contras.

North now is accused of obstructing Congress and making false statements in connection with that letter and two others written in 1985.

"Were you aware that North collaborated with Mr. McFarlane on writing that letter," prosecutor Michael Bromwich asked. "No," responded Barnes.

The ex-congressman said that in a subsequent letter with McFarlane and face-to-face meeting, he requested all documents relating to communications between the United States government and the Contras.

"I felt that Mr. McFarlane was very concerned about our investigation, very nervous about it," Barnes said. He emphasized that "I felt he was very nervous" in the meeting.

Barnes said he rejected McFarlane's offer to examine the documents, saying it was always necessary in such cases to have knowledgeable congressional staffers examine them.

"I wasn't prepared to accept the restrictions" that only he be permitted to look at the documents, said Barnes.

On cross-examination, Sullivan referred to a memo by congressional staffer Johnson five days after the Sept. 12 written denial of Contra assistance.

The memo said that if Congress puts the executive branch in the position of non-disclosure on the Contra issue, that refusal "embarrasses" the administration "and helps us."