The politics of scarcity have replaced the politics of plenty at the Pentagon as defense civilian officials, generals and admirals meet behind closed doors to draft the next five years of President Reagan's rearmament program.

In contrast to 1981 when they could scarcely figure out how to spend all the new money Reagan and his deputies were offering them, the Army, Navy, Air Force, Marine Corps and defense research office today are being told to cut back.

One reason for these new marching orders is Congress' decision to limit the increase in military spending between fiscal 1983 and 1984 to around 4 percent after inflation rather than the 10 percent Reagan requested. There seems little prospect the deficit-minded lawmakers will relent and revoke this decision next year. The Reagan rearmament program will continue, but not at its original pace.

Another reason for the move toward retrenchment in the Pentagon is the growing realization that the services may have overdone it in their buying sprees of 1981 and 1982, ordering even more than they had money to pay for. Many of those purchases are expected to be stretched out or canceled in the new five-year budget plan (fiscal 1985 through 1989) being roughed out in secret meetings of the Defense Resources Board at the Pentagon.

On top of this is a belief among many defense executives, including Deputy Secretary Paul Thayer who is running the DRB meetings, that there must be some reallocation of funds among the military services to strengthen the Army. "The Army hasn't shared in the increased budgets to the same extent as the other services" the last two years, Thayer said.

Pentagon figures show that the Army and Navy budgets went up by almost the same percentages--25.3 and 26.6 percent, respectively, between fiscal 1982 and 1984--while the Air Force's soared by 43 percent. But the Army started at a lower dollar total than its sister services.

In dollar terms, the Army went from $52.2 billion in fiscal 1982 to $65.4 billion requested for 1984.

The Navy, including the Marine Corps, went from $68.8 billion to $87.1 billion, the Air Force, from $65 billion to $92.9 billion.

"It's not that the Army is against the 600-ship Navy," said Gen. E. C. Meyer who, before retiring as Army chief of staff in June, urged Thayer to give a larger slice of the Pentagon budget to the Army. "The issue is do you force yourself in the 1990s to rely on a maritime strategy or do you continue to have a balance of forces that can respond in a unified way with all the service elements?"

As Meyer and his allies inside and outside the Pentagon see it, there must be a different division of the Pentagon budget to prevent the Navy and Air Force from starving the Army. Otherwise, they contend, the United States will not be able to deploy a balanced triple threat of air, land and sea forces in the future.

This argument, along with doubts about whether surface ships could survive the precision weapons the Soviets will have in the 1990s, have helped make the Navy's shipbuilding budget the prime target in the budget deliberations. Navy and Marine leaders are warning their politically powerful constituencies that the Navy could lose $10 billion or more to the Army over the next five years.

Arching over arguments on how the Pentagon's budget should be apportioned among the services are the policy questions of what kind of forces should be built with whatever money becomes available. Here, too, there are shifts and disputes.

Meyer in an interview, said the big change in thinking in regard to tomorrow's Army is that about one-third of it should be light and fast for fighting in the tough terrain of the Third World, like Iran's mountains, while two-thirds should remain heavy in case the United States and its allies have to slug it out with Soviet armor in Europe. Meyer sees a U.S.-Soviet confrontation in central Europe as less likely than some Third World conflict.

The recently retired four-star general said that after Vietnam U.S. policy makers wanted to go back to the traditional heavy divisions that won World War II.

"In 1977, l978 and 1979 the push was on to heavy up all the divisions of the Army," Meyer said. If this had continued, he said, "it would have forced us into having heavy divisions for the next 20 years."

This would have made matters even worse than they are today in terms of finding the planes and ships needed to carry such heavy divisions to distant trouble spots. The giant C5 transport plane, for example, can carry only one M1 tank.

"I favored lighter forces," said Meyer who became chief of staff in June, 1979. His arguments gained impetus in high councils of the Pentagon when the Soviets demonstrated their mobility by invading Afghanistan with impressive speed in December, 1979. U.S. leaders feared the Soviets might move through Afghanistan into Iran. President Carter in his State of the Union Message of January, 1980, tried to discourage such a thrust, declaring,

"An attempt by any outside force to gain control of the Persian Gulf region will be regarded as an assault on the vital interests of the United States of America, and such an assault will be repelled by any means necessary, including military force."

U.S. military leaders were under pressure to make good on this, if necessary. Their immediate answer was a consolidation of existing forces, dubbed the Rapid Deployment Force. It was a paper army then and now. The 82nd Airborne Division, for example, is part of the RDF. It is supposed to be ready to go to war in both Europe and the Persian Gulf. It obviously could not cover both places at once.

To fill that gap, Pentagon and Army leaders are moving to form five light divisions from existing active and reserve forces and equipping them with helicopters, fast armored vehicles and light but lethal modern weapons, including laser-guided shells and "smart" anti-tank and antiaircraft missiles. But this restructuring is expected to require more money than the Army is likely to have if the money is not divvied up differently among the services.

Something has to give. This is what is making Navy and Air Force leaders nervous as Thayer reassesses their programs. Navy Secretary John F. Lehman Jr., who has said the Navy must have "outright superiority" over any combination of adversaries because the United States is "absolutely dependent on the seas for survival," and his ambitious shipbuilding are now under challenge as Pentagon leaders are forced to restructure by subtraction rather than by addition, as was the case in the freer spending days of 1981 and 1982.