The U.S. military, facing the most dramatic transformation in the history of its all-volunteer force, is slashing recruiting quotas, shutting down officer training programs and pushing thousands of unneeded officers out of its ranks in a major new effort to pare the armed services.

Congressional and Defense Department warnings of even harsher cutbacks -- fueled by budget-cutting demands and the rapid, unexpected breakup of the Soviet Union's East European empire -- are creating turmoil at every level of the military, from new service academy graduates uncertain over their futures to senior career officers and enlisted personnel worried about long-awaited retirement benefits.

Military leaders now predict the Pentagon could be forced to slice its 2.1 million armed forces in half by the end of the decade. Congressional committees already have begun calling for troop cuts of up to 140,000 in 1991 alone -- more than three times the number Defense Secretary Richard B. Cheney proposed just six months ago.

While the military traditionally has cut its forces after wars, the U.S. armed forces have never before had to impose such massive reductions in an all-volunteer force.

"The biggest difference is these people want to be here," said Christopher Jehn, assistant secretary of defense for force management and personnel. "We don't have any precedent for what's going on right now."

The services already have begun taking drastic action. While the Army has taken the hardest hits because most of its war fighting capabilities are focused on conventional combat in central Europe -- a scenario that has been all but erased by the virtual dissolution of the Warsaw Pact -- all of the services are being squeezed: The armed forces have accepted 20 percent fewer recruits this year than last year -- about 42,000 fewer men and women.

Thousands of officers and enlisted troops in the Army and Air Force have been offered the chance to leave the service before their commitments have expired.

The Army has begun holding special review boards to determine which officers it will force out of the service. Already it has released about 650 lieutenants against their will.

Last week, the Army announced it is eliminating Reserve Officer Training Corps (ROTC) programs at 50 colleges and is reducing the scholarships it offers cadets because it no longer needs as many young officers.

The Navy, in an effort to cut the costs of advanced training and allow the service greater options in the future for reducing enlisted personnel, has lowered its required service commitment from a minimum of three to two years for recruits.

But those actions are expected to pale in comparison to the kinds of reductions now being debated in Congress and the Pentagon.

When Cheney offered Congress a report illustrating the hypothetical impact of reducing the military 25 percent by 1995, many Congressional leaders said they expect that figure -- about 442,000 people -- to become the minimum level of cuts the military can expect.

"It will be a painful, agonizing process," said Kim G. Wincup, Army assistant secretary for manpower and reserve affairs.

No part of the hard-hit Army is immune -- even the 885 newly minted officers of the Class of 1990 who graduated last month from the U.S. Military Academy at West Point.

"I worry the military will pull out before I get there," said 2nd Lt. Kristin Baker, 22, who has been assigned to an intelligence unit in Germany. "I want to go now while the job still exists."

Baker was a graduate of Lake Braddock High School in Fairfax County and the first woman to hold the academy's top cadet leadership position, an accomplishment that brought her international media attention.

Her class began its plebe year in 1986 as the Reagan military buildup reached its peak, a time when rewarding careers as officers beckoned in the most lavishly funded peacetime military forces in the nation's history.

But even officers from West Point classes as recent as 1987 have been offered the chance to leave active duty two years before their five-year commitment has expired because the service must reduce its officer corps.

"It's scary to wonder where we're going," said 2nd Lt. Malcolm Schaefer, 21, of Schaumburg, Ill., who will be assigned to the 82nd Airborne Division at Fort Bragg, N.C. "There'll be less opportunity to get the battalion command or special unit you want."

"You're going into a profession that is not stable at all," academy superintendent Lt. Gen. Dave R. Palmer told the new second lieutenants earlier this summer as they prepared to embark on their first military assignments. "It's evolving very abruptly."

The changing world events and domestic political trends of the last year have had a major effect on the way many of the new West Point officers have chosen their careers.

Traditionally, positions in armored units with tanks and other heavy conventional weapons -- the heart of the Army -- have been the most favored billets.

Not anymore.

This year, for the first time in the memory of academy officials, "armor" was at the very bottom of the list for most graduates.

"They're thinking, 'If I go armor, I'll go to Europe,' " said Palmer. "What will I do when I get to Europe? I'll be inventorying equipment and putting it in mothballs."

Military leaders, haunted by painful memories of the "hollow" forces of the post-Vietnam era when military units were severely undermanned and the quality of recruits sank, say they worry that the political stampede to find defense cuts will force them to reduce the military too rapidly.

"The balance issue is the most important," said Vice Adm. J. M. Boorda, the Navy's personnel chief. "We want to keep the right people. If we make it miserable enough, the wrong people will leave."

The most agonizing decision for the military, officials said, will be the attempt to weigh cuts in recruits and officers entering the military against firing experienced personnel who had considered the armed forces their career.

"Such a large-scale reduction would face the military services with a difficult choice between sharply reducing the number of new recruits they take in each year or beginning the painful process of involuntarily separating career personnel," the Congressional Budget Office (CBO) said in a new study prepared for the House Armed Services Committee.

The CBO report said the military likely will find itself in a difficult situation, no matter which course it pursues.

If it cuts the number of new troops and officers too severely, it could lead to a serious shortage in future years of experienced personnel for senior leadership posts.

And, if it tosses out too many senior officers, the services will face very difficult morale problems.

"I'm concerned we may be breaking trust with these individuals," said Gary Cooper, the Air Force secretary's manpower chief. "We say America needs you, and these young folks were willing to go to Vietnam. Now comes a time we say we don't need you. That doesn't sit very well with me."

Some of the decisions are so drastic, they will require changes in existing law. The Army, which has a large mid-level officer bulge created by the liberal promotion policies of recent years and anticipates major problems in paring its officer corps, has asked Congress to loosen officer protection laws to make it easier for officers to be forced from active duty, a policy called "involuntary separation."

In an effort to eliminate some of the personal suffering and the image problems associated with those separations, the Defense Department and several members of Congress are proposing a variety of relief efforts, including allowing troops and officers some continued access to military housing, shopping and schools, hefty severance pay and benefits, and assistance in the transition to civilian jobs. Those programs could cost taxpapers several billion dollars, offsetting savings of troop cuts in the first few years, the CBO noted.

But military leaders have discovered that worries over pending force reductions are affecting morale now.

When the Air Force decided it would meet this year's required cuts by offering certain enlisted personnel a chance to leave the service early, it expected to get about 6,000 to 8,000 volunteers. Instead, it was overwhelmed with 17,000 requests. Air Force officials attributed the response to uncertainty over the future of the military.