Military reductions have now touched one of the armed forces' most sacred cows -- its brass.

Defense Department officials announced yesterday that the services will ax 78 general and flag officer positions over the next four years, about 7 percent of its 1,073 top-ranking officer billets.

Joint Chiefs of Staff Chairman Colin L. Powell, a four-star Army general, proposed the cuts, saying, "In light of anticipated force structure changes, we recognize the necessity for general and flag officer requirements . . . to drop below current levels."

Pentagon officials are bracing for a 25 percent cut in strength the next four to five years. There are 2.1 million uniformed members of the armed forces.

The announcement, approved by Defense Secretary Richard B. Cheney, startled mid-level service officials yesterday who were aware that Powell had organized a study of general and flag officer levels, but who were informed of the numbers only minutes before they were released by Defense Department spokesman Pete Williams.

The Army has been ordered to eliminate 33 of its 407 general officer jobs, the Air Force 27 of its 388, the Marine Corps 3 of its 70 positions and the Navy 15 of its 258 flag officer spots.

"Every one of these is going to be a very difficult, agonizing decision," Williams said.

Those senior jobs traditionally have been the most sensitive and political positions in the services. But some members of Congress and others have long argued that the services are top-heavy with brass. Military officials argue that a study commissioned by the Pentagon several years ago said there were too few generals and admirals to run the forces.

The announcement yesterday, however, only served to raise the anxiety level of mid-career officers who see chances of promotion being whittled away by the almost weekly announcements of new force cuts.

Most of the slots will be eliminated through reductions in Army divisions, naval aircraft carrier groups, base closings and other force structure cuts, according to service officials. Military authorities said they can reduce most of the positions through retirements and slowing the number of promotions, adding they do not anticipate any generals or admirals will be dismissed from their jobs.

But Powell has warned the services that these are only the first of even more anticipated reductions in the senior officer corps, according to Williams.

"Both the chairman and the secretary stress that you have to look at force structure reductions at the top as well as throughout the rest of the force, and across all the services," Williams said.

Williams also said yesterday that the offices of the Joint Chiefs of Staff will be reduced 15 percent in the next four years, cutting 240 of 1,627 positions at all levels.

"If we are going to reduce others, we've got to lead the way," said one official on the joint staff.

In a related move, the Army announced it has proposed trimming 7,000 civilian employees, nearly half in Army Materiel Command installations in New Jersey, Pennsylvania and Texas. The command handles research, development and procurement for equipment and weapons as well as troop supply and ammunition production and storage. The proposal would affect 84 jobs in Maryland and 202 in Virginia, the Pentagon said.

Just before Williams launched into an explanation of the general and flag officer cuts yesterday, he announced that the Marine Corps is creating a new three-star billet to head the the 1st Marine Expeditionary Force and the Marine base at Camp Pendleton, Calif. Walter E. Boomer will be promoted to lieutenant general for the job.