There's not much difference in a bomb the Navy drops and a bomb the Air Force drops. Both are made of metal wrapped around an explosive and a fuse. Both can do a great deal of damage to men and materiel.

Further, it turns out, the Army and the Marines can fire many of the same bullets and howitzer shells.

Reasons like those led the Defense Department (under substantial prodding from Capitol Hill and the General Accounting Office) to decree in 1975 that the production and control of ammunition for all the armed forces should come under one tent, the Army's.

But six years later and more than a decade after problems of uncoordinated ammunition management surfaced in Vietnam, the armed forces still don't have one manager over all their ammunition--though someone carries that title.

"There is general agreement the Army does not have the clout it needs to be an effective single manager ," said Jack Bartley, a DOD staff analyst who monitors a program called single manager for conventional ammunition (SMCA).

Ammunition is big business and it is going to get bigger with the Reagan administration's military buildup.

The fiscal 1982 budget shows that Air Force ammunition procurement will jump 3 1/2 times over fiscal 1981, from $344 million to $1.2 billion; Marine ammunition purchasing will go from $80 million to $368 million and Army ammunition procurement from $1.6 billion to $2.4 billion.

Those numbers are going to put even more of a burden on the Pentagon's ammunition production, maintenance and inventory control programs, according to the experts.

Interservice rivalries and suspicions have substantially hampered the single manager effort to date, according to GAO and Pentagon officials.

The single manager controls 60 percent of the armed forces' $16 billion store of non-nuclear ammunition; the individual services control the rest.

There have been arguments over who should maintain ammunition here and abroad and who should pay whom and when. Individual services sometimes have delayed sending their ammunition money over to the single manager, who thus was unable to pay suppliers.

Each military service still maintains control of its own ammunition inventory, which means ammunition can be hidden from the single manager. The single manager is an Army general physically located in Rock Island, Ill., hundreds of miles from the pushing and shoving in Washington, where it might be easier to get something done.

Some of those problems--but not all of them--were addressed in a new DOD directive issued last November that is supposed to give the single manager more power. The new directive, watered-down from an earlier draft, according to sources, was adopted the day before Rep. Jack Brooks' House Government Operations Committee held hearings on the effectiveness of the single manager.

For the past three years, GAO's Werner Grosshans told the committee, DOD "progress toward fully implementing the single manager concept has been at a virtual standstill." The new directive, Grosshans said, "falls far short of assigning the single manager the responsibility and authority needed to effectively manage this area."

Sources point out that ammunition, regardless of who is going to explode it, is basically the same thing: metal, explosives and propellants, some kind of packing arrangement and a fuse (which tells a bomb whether to blow up 50 feet above the ground or to wait until it hits something).

Because of that, the individual services, maintaining their own programs, often compete for the same production facilities and thus drive up each other's prices, according to military and congressional sources.

"During peacetime," DOD's Bartley explained, "a lot of ammunition is to be stockpiled, not used. Nonetheless, you want to be able to maintain a 'warm base' so you could go to wartime production if necessary.

"Now that we're talking about greatly increasing production by two or three times, we're going to create a bulge in the system. When that bulge calms down, what do we do with the facilities?"

Another problem is what to do with ammunition that has been stockpiled. The GAO, in a tour of ammunition dumps, discovered that much ammunition is in need of maintenance. Again, management is a problem. The single manager, for example, maintains the Navy's ammunition stateside. Overseas, the Navy leaves it in dumps manned by relatively inexperienced Navy personnel.

It's not all negative. The GAO says that even the partial single manager system in place for the past six years has resulted in "cost avoidance" of about $200 million. "For example," GAO said, "a trade involving Marine Corps mortar ammunition and Army howitzer ammunition resulted in a procurement avoidance of $41 million."

One of the most puzzling aspects of the issue to an outsider is why, with Defense Department agreement that a strong single manager is needed, somebody doesn't just issue an order saying, "Do it!"

But the department can be very wary of stepping on the toes of the services. Thus, its tough new directive was sent back and forth between the services and the department for several years before political pressure from Capitol Hill forced the watered-down compromise to be adopted.

"If you don't want something to happen," DOD's Bartley said, "this kind of structure makes it possible."

A congressional source put it another way. "When it comes to the three- and four-star generals, DOD is a democracy. Only at the bottom is it a dictatorship. These guys rule by consensus. The secretary of defense will not issue a directive unless there is a consensus."