President Reagan's national security affairs adviser, William P. Clark, yesterday took his first steps to reshape the National Security Council, naming his deputy and three consultants, including Claire Boothe Luce and William F. Buckley.

Clark, who replaced Richard V. Allen as national security adviser earlier this month with the power to expand the job's powers, appointed Robert C. McFarlane as his deputy. McFarlane worked on the National Security Council from 1973 to 1977 under Presidents Nixon and Ford. In the Reagan administration he has been the counselor of the State Department.

McFarlane has been closely associated with Secretary of State Alexander M. Haig Jr. He also worked on Capitol Hill for Sen. John G. Tower (R-Tex.), chairman of the Senate Armed Services Committee.

McFarlane replaces Adm. James W. Nance, who was Allen's deputy and then became the acting national security adviser when Allen took a leave of absence Nov. 29 in what proved an unsuccessful attempt to save his job by speaking out in defense of his conduct.

Clark, echoing other top White House officials, praised Nance's performance at the NSC while announcing his replacement. Nance will be put in charge of "special projects," White House deputy press secretary Larry Speakes said.

Clark announced that Luce, 78, will be a consultant to the NSC on intelligence. She was a member of Congress from Connecticut from 1943 to 1947 and the U.S. ambassador to Italy from 1953 to 1957. She is the widow of Time magazine founder Henry Luce.

Buckley, 56, was named consultant for policy planning. He is the editor-in-chief of the National Review, a columnist and the author of numerous books.

Thomas C. Reed, 47, was named consultant on defense. He is a business executive who was secretary of the Air Force from 1976 to 1977.

Clark said the three will assist him in restructuring the NSC staff. Their appointments are effective immediately and will last 30 days, he said. They will receive "reasonable and necessary" expenses.

Clark, who was deputy secretary of state until moving to the White House, announced that he is bringing two assistants from State with him.

Jeremiah O'Leary, former White House correspondent for The Washington Star and a retired Marine colonel, will be a special assistant to Clark specializing in press relations.

Richard C. Morris will be another special assistant. He was a research attorney for Clark when Clark was a justice of the California Supreme Court, and he was Clark's executive assistant in the State Department.