THERE WILL BE less than meets the eye from a policy standpoint when official Washington turns out this week to commemorate the changing of the guard on the nation's highest military body, the Joint Chiefs of Staff.

The marching bands, flyovers by aircraft and the salutes between glistening generals and admirals at ceremonies at the Pentagon, Andrews Air Force Base and the Naval Academy Friday and Saturday will belie the reality.

That reality, uncomfortable for the generals and admirals and their following to admit, is that the Joint Chiefs of Staff have declined in influence since World War II to the point that they are close to being a ceremonial body needed only for special occasions. Rather than regarding the chiefs as fellow policy executives running the corporation, presidents for almost two decades now have relegated them to the role of a somewhat bothersome board of directors that must be won over for appearances on some policy initiatives.

President Kennedy, who lambasted the chiefs to associates for their alleged failure to speak their doubts about the disastrous Bay of Pigs invasion of 1961, gladly let his defense secretary. Robert S. McNamara, take command of the Pentagon and the military policy that flowed out of it. The chiefs was wooed to support the nuclear test ban treaty, but otherwise were eclipsed by McNamara and his "Whiz Kids."

President Johnson, who faulted the chiefs for not taking the broad view of defense policy, nevertheless felt the need to be photographed with one or more of them to project an image of corporate unity when he escalated the Vietnam War. The chiefs stood still (or sat on the White House couch) for such photographs. Not one of them resigned to protest the Vietnam War policies they later assailed.

President Nixon's admiration of military men, dramatized by his repeated viewing of the movie "Patton" while in the White House, did not carry over to taking the chiefs into his confidence. Nixon let Henry Kissinger chart policy for the Vietnam War, arms control and keeping troops in Korea.

The chiefs and their staff felt so frozen out of the big policy decisions in 1970 and 1971 that Rear Adm. Robert O. Welander, head of the Joint Chiefs' liaison office at the White House, was "a cognizant participant" - to use the description in the Senate Armed Services Committee report on the episode - in surreptitiously sending secret National Security Council papers to Adm. Thomas H. Moorer, then chairman of the Joint Chiefs.

President Ford, who as ranking Republican on the House defense appropriations subcommittee had developed a close and comfortable relationship with military leaders, in time might have restored some of the chiefs' lost prestige and power, but his White House tenure was too brief to know that for sure.

President Carter, from shortly after his election onward, has made a point of consulting with the chiefs. But the record to date dows not indicate the chiefs have been especially influential on his major military decisions. Carter, against the advice of the chiefs, scrapped the B1 bomber, has delayed his decision on producing the neutron bomb, and is moving to negotiate a complete ban on underground nuclear testing. Outside the Chain of Command

FROM THAT BRIEF rundown, one can see that the chiefs are not really galloping over the country as generals on horseback bent on taking over the country in "Seven Days in May" fashion. They are instead, first, presidential advisers whose advice need neither be sought nor followed and, second, managers and implements of policies decided by others, not necessarily with their advice and consent.

No general or admiral on the Joint Chiefs of Staff commands a single combat battalion or ship. An order to march against Russia would go from the president to the secretary of defense to the field commander in Europe.

Because of laws passed by a Congress worried about the Joint Chiefs becoming Prussian-like, as well as executive orders defining and redefining the chiefs' role, the chiefs have been pushed out of the mainstream of command. This is also true of the secretaries of the Army, Navy and Air Force - as evidenced with embarassing clarity when former Air Force Secretary Robert C. Seamans Jr. had to admit publicly that he was away skiing when President Nixon ordered the 1972 Christmas bombing of North Vietnam and had been neither consulted nor informed about it.

So what does this little understood and largely overrated military body of three four-star generals and a full admiral really do? What kind of men are being selected these days for chiefs? And could the Joint Chiefs, or a body of military officers like it, be more influential and illuminating on life and death military questions?

In contrast to the glory days of World War II when President Roosevelt established a body representing the Army, Army air forces and Navy to coordinate war operations with the British general staff, the chiefs today pretty much "manage" the people, money and weapons they are given by the president and secretary of defense. They also devise on military issues, usually through their chairman, the president, the defense secretary and the National Security Council - at least if their advices is requested - and keep undating a master plan known a JSOP (for Joint Strategic Objectives Plan).

Their chairman, who by laws is relieved of duties to his individual service so he can devote full time to running the Joint Chiefs, is backed up by a staff of 400 officers drawn from the Army, Navy, Air Force and Marine Corps. This "joint staff" has become a "prestigous burial ground" for officers who missed advancement, to quote one critic. The 400 work up analyses and position papers for the chiefs under a cumbersome system in which progress is marked by the color of the paper.

The staff paper starts out on a what is called "a flimsy" of white paper, advances onto tan paper after the first of a series of approvals is given; and moves onto green paper when it is ready to be laid on the table the chiefs sit around in their Pentagon conference room located on to the left of the river entrance. If a chief does not like something in the proposal or report, he writes "a purple" expressing how he would like to changed. After the paper is amended to satisfy "the purples," a diagonal red stripe is drawn across the amended version - signifying that it has been approved by the Joint Chiefs. This process, according to officers who have participated in it, almost always takes at least a week and usually two.

"What you have after all this work," says one Army officer, "is the lowest common denominator," a mush paper of compromises that policymakers neither want nor can use. Innovation, bold ideas, fresh approaches to old problems - these fall out as the Joint Staff papers get massaged by competing service interests. This process, critics contend, is why secretaries of defense and presidents turn to their own staffs rather than to the chiefs for ideas, assessments and recommendations.

"If I were a politician," remarks an Army officer who has been deeply involved in the Pentagon planning process, "I wouldn't pay any attention to the chiefs. They have not developed any constituency. If the chairman of the Joint Chiefs registered in a motel, nobody would recognize his name. The last chairman of the chiefs who had anything approaching a constituency was Maxwell Taylor. If I were a politician, I would know that the chiefs couldn't do me any good or any harm."

Military officers interviewed say they would not advocate that the chiefs set out to build a political base, as Adm. H. G. Rickover has done in Congress, but that they find ways to make today's military leadership creative and illuminating, more helpful and influential. Turning Corporate Gray

A COUNTERARGUMENT can be made that the chiefs are bright, honorable, patriotic leaders doing the most they can within the severe restraints imposed by civilian authorities they are sworn to obey and support. It can be further argued that today's chiefs must wrestle with the same problems as corporate vice presidents - cash flow, personnel problems, product research - and thus are being chosen more for their technical and managerial abilities than for their combat records. The chiefs' coloration is becoming corporate gray as a result.

Consider, for example, the contrast between the cigar-chomping, tough-talking, bomb-them-back-to-the-Stone-Age Gen. Curtis E. LeMay, who was Air Force chief of staff from 1961 to 1965, with the Air Force general President Carter and Defense Secretary Harold Brown have selected for that same job, effective July 1, Lew Allen Jr.

The 52-year-old Allen, to quote from his official Air Force biography, in 1950 "entered the University of Illinois for graduate training in nuclear physics and received a master of science degree in 1952. He earned his doctorate degree in physics in 1954 after completing an experimental thesis on high-energy photonuclear reactions . . . In December, 1961, Gen. Allen was assigned to the Office of the Secretary of Defense in the Space Technology Office of the Directors of Defense, Research and Engineering . . . In August, 1973, he became director, National Security Agency . . ."

Similarly, Air Force Gen. David C. Jones, whom Carter has named to succeed Air Force Gen. George S. Brown as chairman of the Joint Chiefs, is a soft-spoken, managerial type who took an intellectual rather than a combative approach to the possibility of unionization of the military, declaring publicly that it could happen. He has been discussing the issue calmly with such outside experts as Arthur Goldberg, former labor secretary and Supreme Court justice.

Gen. Bernard W. Rogers, Army chief of staff, provides further evidence of the new breed running the nation's military. After graduating from West Point, Rogers attended Oxford University from 1947 to 1950 as a Rhodes scholar, receiving a bachelor of arts and master of arts in philosophy, politics and economics.

Adm. Thomas B. Hayward, President Carter's choice for chief of naval operations, who will represent his service on the Joint Chiefs starting July 1, is a former test pilot and former skipper of several ships who holds a masters of science degree in international affairs from George Washington University and was previously director of the Navy's office of program planning.

Gen. Louis H. Wilson, the Marine Corps commandant who sits as a member of the Joint Chiefs when the agenda includes items of interest to his service, is a highly decorated combat soldier, a Medal of Honor winner, but also a deep-thinking, soft-spoken executive when discussing issues facing the corps - such as abuse of recruits by the old breed of Marine drill instructor.

Sen. Henry M. Jackson (D-Wash.), an influential member of Congress on such key military issues as the strategic arms limitations talks, is far from happy with the managerial, get-along manner sometimes displayed by the chiefs.

No one can deny that the questions facing today's chiefs are more complicated than ever, with technology driving exotic weapons for fighting in space, on the ground, and in the ocean depths.

But one longtime participant in both military planning and actual combat argues that the nation dare not let technology remain the driving force for military strategy. He asserts that the Joint Chiefs, partly because of the compromises they have made along the way to get to the top of the military, cannot provide the fresh military thinking needed.

Nor, this critic contends, can the nation safely rely on the kind of military advice coming from recent and present defense secretaries, Pentagon systems analysts and White House military advisers. Too often, he says, they have never led a platoon, driven a tank or experienced the confusion of combat. Their advice, therefore, no matter how much it is quantified, is seldom practical - as Vietnam proved.

This critic's idea, which other officers say is of least worth considering, is to provide the nation with a new resource of military analysis and advice by selecting a group of bright and experienced officers from each of the services; offering them civil service jobs so they would not be beholden to their military superiors, and putting them to work on the big questions of military policy. Then and only then, this officer contends, will the nation be forced into a healthy debate on the practical options, options which the Joint Chiefs cannot provide.