Once again, US Secretary of State Alexander M. Haig Jr. appears to be at odds with another high-ranking member of the Reagan administration, this time over NATO policy.
In testimony before Congress Thursday, Mr. Haig's contention earlier that NATO defense plans include the option of detonating a nuclear device as a ''demonstration'' during a conflict with Warsaw Pact troops was flatly denied by Secretary of Defense Caspar W. Weinberger.
Haig told the Senate Foreign Relations Committee Wednesday that there are ''contingency plans in the NATO doctrine to fire a nuclear weapon for demonstrative purposes to demonstrate to the other side they are exceeding the limits of toleration in the conventional areas - all designed to maintain violence at the lowest level.''
Thursday, Mr. Weinberger told the Senate Armed Services Committee that the plan was merely ''a suggestion in the 1960s of some one of the military planners. . . . There is absolutely nothing in any of the plans that I know of that contains anything remotely resembling it - nor should it.''
Apart from the merits or demerits of the idea is the impact the apparent disagreement may have on a Western Europe already uneasy over US military intentions on that continent.
President Reagan's decision to resume production of neutron warheads and NATO's decision to deploy nuclear-tipped Pershing II missiles have spawned the biggest, most vocal antinuclear movement in Europe since World War II.
Mr. Reagan stunned many Europeans two weeks ago by telling a group of editors visiting the White House that he ''could see where you could have the exchange of tactical (nuclear) weapons against troops in the field without it bringing either one of the major powers to pushing the button.''
And now there appears to be a disagreement at the highest levels of US diplomatic and defense planning over the existence of a NATO contingency plan involving the use of nuclear weapons.
The demonstration concept is not new. At the end of World War II, President Truman was offered the option of dropping a ''demonstration'' bomb on an uninhabited Pacific island to get the Japanese to surrender. Some observers say a similar plan today would give NATO commanders a ''fallback position,'' allowing them to point to the danger of escalating the conflict, without risking an immediate, all-out response.