PRESIDENT REAGAN'S decision to switch to a radar-deceiving "stealth" version of the air launched cruise missile involves a deliberate deception of Americans (in hope of fooling the Kremlin at the same time). It also raises significant questions about other strategic weapons now under construction.

A year ago the president submitted to Congress a defense budget which called for buying 440 air launched cruise missiles (ALCM B's) for $872 million in fiscal 1984, which begins next Oct. 1. This part of the ALCM B procurement plan was set down in the official Reagan administration budget documents released to the Congress and the public.

However, late last year the Pentagon secretly told a few members of the House and Senate that the ALCM B program in the president's budget was not the real plan; that the Air Force planned to switch this year to the stealth version of the ALCM B, known as the Advanced Cruise Missile, to make it even harder for the Soviets to build a defense against this new nuclear weapon.

In other words, the Pentagon -- presumably with the blessing of President Reagan and Defense Secretary Caspar W. Weinberger -- took it upon itself to deceive some of the Congress and all of the public in the apparent belief that the right to lie for national defense is fully justified, even in peacetime. And those Senators and Representatives who were told about the deception knowingly went along without protest.

It seems quite a risk to jeopardize public faith in the veracity of the government for the sake of fooling the Russians for just a year about precisely which cruise missile the United States plans to put on its airplanes. For that small and immeasurable benefit, the Reagan administration has brought into question the integrity of the budget process and of the congressional committee system, not to mention the credibility of Reagan, Weinberger and Air Force leaders. Not many years ago, deception of the public by civilian and military leaders (remember Air Force Gen. John D. Lavelle's two sets of books on bombing in Southeast Asia?) helped tear the country apart during the dark days of Vietnam.

Weinberger raised the question of the government's right to lie in another context last week. He was asked why, in his news conference on Feb. 16, when asked about American military moves in regard to Libya, President Reagan said of the aircraft carfier Nimitz: "I don't believe that there's been any naval movement of any kind. . .There, as I say, has been no naval movement at all."

That statement stunned Navy leaders who knew the Nimitz had already left its post off Lebanon and was operating in the central Mediterranean, with its planes flying over the Gulf of Sidra off Libya. Could the Nimitz have been sent into a troubled area without Reagan knowing about it? Morning-after explanations from high Navy and White House officials were that Reagan of course knew the Nimitz had left Lebanon, but did not consider its move to the central Mediterranean related to the Libyan crisis and therefore excluded it from his response about that situation.

Weinberger came up with a different explanation on Thursday, declaring: "I think the assumption that because a question is asked it has to be immediately answered when you are dealing with movements of ships or troops or planes or men is an assumption that isn't really warranted. I think that the movement of ships, planes, forces of any kind is a matter that has to be treated with discretion and guarded in the sense that we don't want to do anything that risks the lives of anybody aboard. . .So I don't think there was any gap or any lack of communication or anything that needed clarification or any errors made by anybody. It's exactly what I think everybody should expect when questions are getting into sensitive areas where we do want to make sure that we don't do or say anything that in any way risks anybody's life."

Air Force leaders have not publicly acknowledged that they used the fiscal 1983 budget documents to try to deceive the Russians about plans for fiscal 1974. But they have justified the switch to radar-deceiving "stealth" cruise missiles by noting that Soviet air defenses are steadily improving. Publicly, Air Force leaders have said that the Soviets' SA10 anti-aircraft missile might be able to knock down the ALCM B, which flies close to the ground like a drone aircraft.

But if new Soviet capability justifies switching stealth technology for the ALCM B, would it also justify trading up at once from the B1 bomber to a new stealth bomber? The B1 presumably suffers from the same kind of vulnerability as the ALCM B. It is supposed to be ready for duty in 1986, the flying wing Stealth in 1991.

And if Soviet defenses are getting good enough to threaten the ALCM B, why is not the Tomahawk cruise missile Reagan wants to deploy in Europe -- whose technology is essentially idential to the ALCM B -- equally vulnerable?

And if the cruise missile, the B1 and stealth bombers are really for use only after the Soviet Union has fired first, as the administration says, presumably American land and submarine missiles would have been fired ahead of them to blow away Sovet air defenses. So why all this emphasis on being able to penetrate Soviet anti-aircraft defenses which would not exist if doomsday ever did come?

The Air Force has answers for all these questions -- if anyone in Congress bothers to ask them. One can hope that this time around, the Air Force will answer the questions directly, without playing the dangerous game of using official documents to deceive the American public in hopes of fooling the Kremlin. The Soviets probably plan for the worst anyhow when building their defenses.