Maj. Gen. Robert L. Schweitzer, supposedly fired from his National Security Council job Oct. 20, actually was kept on at the White House long after that, the Army confirmed yesterday.

Brig. Gen. Lyle J. Barker, Army spokesman, said Schweitzer, who was dismissed for making unauthorized remarks about the Soviets being ready "to strike," did not pass from White House to Army control until Nov. 14 and may well have worked on leftover projects at the NSC until recently.

Administration officials confirmed that was the case, noting that the general's frequent comings and goings in civilian clothes to his old White House office became something of a joke among fellow staffers as the weeks wore on after the announcement of his dismissal.

Richard V. Allen, the NSC director who fired Schweitzer for failing to clear his "Russians are coming" speech to the Association of the U.S. Army, ignored warnings from colleagues that it would be embarrassing if the press found out how long Schweitzer was being kept on, sources said.

Army officials until yesterday refused to answer questions about when Schweitzer had left the White House and what his next job would be. Pentagon sources said the silent treatment had been ordered by Gen. E.C. Meyer, Army chief of staff. After being apprised yesterday of the Army's position, Henry E. Catto Jr., assistant secretary of defense for public affairs, demanded that the Army start being responsive, sources said.

In his controversial speech, Schweitzer said there was a "drift toward war" and that the "Soviets are on the move; they are going to strike." But President Reagan gave Schweitzer a friendly farewell in a ceremony in the White House Oval Office shortly after Allen announced the general's dismissal from the NSC staff.

Schweitzer at the time expressed no bitterness about his dismissal, declaring: "Like any soldier worth his salt, I'd rather be with troops, with people, than working a desk."