Paradoxical as it may seem in the middle of a costly, full-scale war, the Pentagon will send Congress a 1992 budget next week that will continue the United States on the track of declining defense spending.

The budget proposal will seek money for four B-2 "stealth" bombers, at least $1 billion more than is authorized this year for the Strategic Defense Initiative (SDI) and certain concepts and weapons that have proved particularly valuable in the Persian Gulf War, according to congressional sources.

But the biggest influence on the Defense Department budget that will be released Monday will be the huge federal deficit, not Operation Desert Storm, the sources add.

"The minute Desert Storm is over the money's going to dry up," Rep. John P. Murtha (D-Pa.), chairman of the House Appropriations defense subcommittee, said this week. Referring to reports of an increased request for SDI, he said, "The money is not there for all these things. We have to adapt to the threat and the amount of money available."

The five-year deficit-reduction plan ratified by Congress and the White House last fall committed the administration to smaller military budgets. In addition, Defense Secretary Richard B. Cheney has said he hopes to reduce the size of U.S. military forces by 25 percent within five years.

Under the deficit-reduction deal, regardless of inflation, total defense outlays in fiscal 1992 can be no more than $294.3 billion, down from $296.4 billion this year. "That's set in stone," one congressional aide said.

But the deficit-reduction plan exempted the Persian Gulf operation from the 1992 defense budget, so next week's proposal will vastly understate actual defense costs. The cost of the war, including replacement of missiles and equipment, will be covered in one or more separate money requests.

But it is uncertain whether the gulf operation will be a bonanza for defense contractors feeling the pinch of more-austere military budgets. While Pentagon planners may want to replace hundreds of millions of dollars worth of Patriot, Tomahawk, Hellfire and other missiles that are being expended in the gulf conflict, other items, such as certain fighter aircraft, could become unnecessary in light of longer-term Defense Department plans.

Top defense officials, for example, are considering elimination of two of 14 U.S. aircraft carrier battle groups, and seven of 35 air wings.

A prolonged ground war could take a heavy toll on equipment such as the General Dynamics M-1 tank, McDonnell Douglas AH-64A Apache helicopters and artillery. But defense spending foes in Congress are likely to argue that that equipment would have been withdrawn from a front-line role in Europe anyway as a result of East-West force reductions.

As a result, the estimated $500 million to $1 billion a day the war is costing may not all be passed back to U.S. taxpayers or the coalition allies.

Even so, the need to fight a war of unknown duration while planning for a smaller military has set the stage for one of the noisiest appropriations free-for-alls in memory.

Supporters of the Air Force's B-2 "stealth" bomber, such as Rep. Norman D. Dicks (D-Wash.), argue that the success of the F-117A "stealth" fighter in the gulf demonstrates the advantages of that technology. Critics argue that the war proves the costly Northrop plane, which has not been used, is unnecessary to gain air supremacy in the kind of wars the United States is likely to be fighting in coming decades.

Congress has authorized production of 15 operational B-2s, and three others for testing.

The B-2 debate suggests that the gulf war will have an impact on the final shape of the 1992 defense budget even though the planning and funding are supposed to be separate.

"Everything's related in some way to Desert Storm," Murtha said. "That includes recruiting, training and everything else."

An example of that is the uncertainty over the effect of the war on military manpower. The current defense budget calls for active-duty forces to be reduced by 100,000 by Oct. 1, 42,000 from the Army. That now seems an impossible target in light of the thousands of troops needed for Desert Storm, congressional sources said. Cheney last year authorized service commanders to extend enlistments of personnel and to defer retirements.

Budget experts say that could add some $2.8 billion in military pay in fiscal 1991 and 1992. That is a relatively small amount in a budget of nearly $300 billion. But it could have more serious long-term effects.

The Bush administration had planned to reduce active-duty personnel from 2 million to 1.7 million by 1995. But those numbers could now slide, defense experts say. That, in turn, would postpone the overall force reductions that will be required for significant budgetary savings later in the decade.

To the dismay of SDI critics, congressional supporters of the strategic missile defense have seized on the success of the Patriot in Israel and Saudi Arabia to buttress their case for more money.

However, said Rep. Les AuCoin (D-Ore.), a member of the Appropriations defense subcommittee, "Patriot doesn't prove that SDI works. It proves that Patriot can work extremely well against offensive tactical missiles that are two or three decades behind its technology and are slow, dumb and come in ones and twos with conventional warheads. That's what it proves and nothing more."

AuCoin has been a strong backer of the Arrow, a U.S-Israeli anti-missile weapon being developed under SDI. Like Patriot, Arrow is ground based. But it can intercept incoming missiles at greater ranges and its kinetic energy warhead is supposed to effectively destroy enemy chemical or biological warheads.

Further complicating this year's debate is the fact that many of the weapons fielded now in the Persian Gulf, such as Patriot and the Apache helicopter, are based on older technologies. Some military planners want to press ahead quickly with development of futuristic new weapons such as the LH helicopter. But if the weapons now on the battlefield perform well they could provide an argument for postponing the move to newer, unproved systems.