Secretary of State Edmund Muskie yesterday defended the Carter administration's controversial recent reformulation of U.S. nuclear strategy, telling Congress that it "does not signify a shift to a war-fighting strategy nor to a first-strike doctrine" against the Soviet Union.

Muskie and Defense Secretary Harold Brown appeared at a closed-door session of the Senate Foreign Relations Committee and according to committee aides, were questioned by several senators concerned that the new presidential directive on nuclear strategy might mean that the United States is now moving toward the idea that limited nuclear wars could be fought and won.

Committee Chairman Sen. Frank Church (D-Idaho) told reporters later that both Brown and Muskie "emphasized to the committee that neither they, nor President Carter, believe it likely that a nuclear war, once begun, can stay limited. Nor do they believe," Church said, "that there is such a thing as a 'winnable' nuclear exchange between superpowers."

Sen. Jacob Javits (R-N.Y.), the ranking minority member of the committee, told reporters that what now is necessary is for the Soviet Union, "which has given the world the impression that [it believes] nuclear war is winnable and [thus] possible," to qualify those views.

In July, President Carter signed Presidential Directive 59 which, as administration officials privately explained it, modified the strategy the United States would use in fighting a nuclear war. It would put relatively more emphasis than in the past on hitting military targets and Soviet military and political command centers early in an encounter as a means to convince the Soviets that they could not win an expanded and continued nuclear exchange.

The directive itself, which is highly classified, has never been made public. And, in part because its existence was made known first by the press rather than the government, it has cause considerable controversy and concern in some quarters in this country and in Moscow.

Muskie, a former member of the Senate committee and one who was critical of the new U.S. strategy when it first began to emerge in 1974, went to some lengths yesterday to make sure both Congress and Moscow understand what it means.

Muskie said the new directive "underscores -- and I believe strenghtens -- the credibility of our capability to relatiate against any nuclear attack under any circumstance, be it a massive strike against the U.S., or a more limited one against our forces or our allies."

"We want to make sure the Soviets gee that message. But we also want to ensure that they get the message right," Muskie said.

"I do not want anyone to wrongly conclude that we suddenly have become confident about our ability to orchestrate nuclear exchanges and control escalation, or that we have become complacent about the use of nuclear weapons."

Asked why he had changed his own views since 1974, when he was skeptical about then-proposed strategy changes, Muskie said there have been technical developments on both sides that changed the picture, changes in capabilities and in perceptions about the possibilities of limited nuclear war. c

Brown cited some recent writings in which Soviet Marshall Nikolai V. Ogarkov discussed possible "victory" in the event of nuclear war to buttress the administration case that discouraged the Soviet notion of victory in atomic warfare.

The directive was also controversial because Muskie, as secretary of state, was left out of administration deliberations leading to its adoption.