The Pentagon, facing its sharpest budget cuts since the Reagan administration began, is grappling with financial and political decisions that could affect the armed forces and the weapons they use for years to come.

The internal debates over cutbacks have touched virtually every phase of the military, from the size of forces to the number of new barracks that will be built to the types of new weapons that will be used in combat.

Although top Defense Department officials are in the midst of sifting through dozens of proposals, many of which may never be imposed, the military is bracing for major cutbacks in numerous areas, according to interviews with officials in each service.

The budget reductions have been ordered by Defense Secretary Frank C. Carlucci in response to congressional demands for decreasing the massive federal deficit in the 1989 fiscal year budget.

Almost two months ago Carlucci told Pentagon leaders to slash about $33 billion from their proposed $332 billion budget for 1989. He has since mandated that the services make additional cuts of more than $1 billion.

While the amount of money the Pentagon will be authorized to spend in 1989 is expected to be about $7.5 billion more than its 1988 authorization of $292 billion, it is far less than the increases that were routinely given to the armed forces in the early years of the Reagan administration.

The new demands for cutbacks come at the same time that some internal Pentagon studies are showing that the Defense Department will be unable to finance much of the buildup started in those early Reagan years.

As a result, cuts being debated in the Pentagon have raised serious questions for military leaders, according to Adm. Carlisle A.H. Trost, chief of naval operations.

"Where are we headed? Is this the beginning of the same kinds of problems we saw in the 1970s? Will we be able to protect our people from the turbulence, or will they start 'voting with their feet' again?" Trost mused during a recent change-of-command ceremony in Norfolk.

Trost added, "We are right to be watchful. But it is much too soon to become alarmed."

Some of the service proposals blatantly contradict orders issued by Carlucci when he asked for cuts.

The Army, for example, proposed slowing production of some weapons such as the M1 tank, the Bradley Fighting Vehicle, helicopters and heavy air defense programs, after Carlucci told the services he would not tolerate use of that longtime tactic for immediate money savings. Carlucci told the services they would have to eliminate some weapons programs, rather than "stretch out" large numbers of systems.

When Carlucci told the services they would have to reduce personnel, the Army sent back a proposal to cut a mere 100 troops, saying the Army already has reached the lowest troop levels in recent history.

Carlucci's top deputy, William H. Taft IV, responded by telling the Army to cut its active duty force by 10,000 -- to 771,000 troops by October 1989. Taft also imposed another $1 billion budget cut on top of the $9 billion reduction Carlucci already had ordered for the Army.

Other services turned in some proposals that were almost certain to be overturned. The Navy, ordered to cut its budget by a $11.6 billion, suggested eliminating a $1.4 billion Trident missile submarine, a recommendation that Carlucci immediately vetoed because of the importance of the program, according to Navy officials.

"None of the budgets will come out quite the way the services want them," one Pentagon official said.

The internal budget debates are far from over, according to Pentagon officials. One Air Force official monitoring the budget battles said, "Everything is changing on the hour."

The Office of Management and Budget has told Congress it hopes to relay the agencies' 1989 budget proposals by mid-February, about six weeks behind schedule. The Pentagon and other federal agencies were forced to start working on proposals for 1989 cuts before the 1988 fiscal year total had been determined by Congress, leaving them behind schedule.

Other proposals are under scrutiny by senior Defense Department officials. In the Air Force, facing total cuts of $10.5 billion, they include:

Killing research and development for an antisatellite missile that would be mounted on an F15 fighter, which would launch the missile into space. The savings for fiscal 1989 would be about $500 million. Cutting about 20,000 members of the service, reducing strength to 577,750 in 1989.

Eliminating two active tactical fighter wings and three reserve squadrons, about 100 aircraft.

Cutting the Small Intercontinental Ballistic Missile (Midgetman) program, which has been controversial in Congress.

In the Army, facing cuts of $10 billion, proposals call for:

Killing the controversial Aquila robot reconnaissance aircraft and the Copperhead laser-guided artillery round. Slashing budgets for new family housing by about 80 percent and planned renovations for existing units by more than two-thirds.

In the Navy, facing cuts of $11.5 billion, proposals include:

Sending 16 active-duty destroyers to the reserve fleet, where there would be fewer manpower requirements.

Cutting out one of the two Aegis cruisers -- among the most heavily armed surface ships in the Navy -- requested for 1989 at a savings of almost $1 billion.

Reducing the number of AV8B Harrier vertical-takeoff aircraft from 32 to 24.

Eliminating plans for dozens of modernizations and improvements to aircraft, ships and weapons systems.

Slashing some procurement programs by as much as 25 percent.

In other budget-related actions, Carlucci notified service secretaries Monday that he will initiate congressionally mandated changes in officer allocations for fiscal year 1988, but will not yet implement a Hill-requested 2 percent cut in 1989 pending completion of a study showing the impact of those cuts to Congress by March 1.

The changes in officer allocations mandated by Congress for 1988 mean a reduction of 1,514 officers in the Army, 2,255 in the Air Force, with an increase of 559 in the Navy and 122 in the Marine Corps. Overall, the figures represent a 1 percent cut in military officers.