The Senate Armed Services Committee, traditionally the Defense Department's most loyal supporter in Congress, overrode strong objections from Pentagon leaders yesterday and unanimously approved a major military reorganization.

Committee leaders said the bill would encourage the four branches of military service to cooperate more and compete less. It would strengthen the chairman of the Joint Chiefs of Staff, create a vice chairman and give more authority to combat commanders in the field.

The committee also voted 19 to 0 to eliminate 17,694 jobs, trimming headquarters and administrative bureaucracies by about 10 percent. To improve weapons procurement, the bill would create an undersecretary of defense to oversee acquisition, while taking modest steps to reduce congressional interference.

Senators said that the committee's unanimous vote, combined with a similar but less far-reaching bill approved by the House last year, makes approval of a reorganization plan this year very likely.

Sen. Sam Nunn (D-Ga.), the committee's ranking minority member, said the "sweeping and historic" legislation would help remedy problems "that have plagued our national defense for decades." Chairman Barry Goldwater (R-Ariz.) called the bill "the most significant piece of defense organization legislation in the nation's history."

Goldwater also said his committee "has had to fight elements of the Pentagon every inch of the way."

Those elements were led by Navy Secretary John F. Lehman Jr., who wrote the committee members that some provisions in their draft bill "would make a hash of our defense structure."

In other letters submitted before final markup, Defense Secretary Caspar W. Weinberger questioned the constitutionality of certain provisions; Air Force Secretary Russell Rourke predicted "very adverse consequences"; the chief of naval operations, Adm. James D. Watkins, called the bill "terribly flawed and certainly not in the best interests of national security"; and the Marine commandant, Gen. P.X. Kelley, said the bill "would create chaos."

"If the 'draft bill' were to be enacted in its current form it would result in a significant degradation in the efficiency and effectiveness of the defense establishment -- to the point where I would have deep concerns for the future security of the United States," Kelley said. "In this regard, I know of no document which has concerned me more in my 36 years of uniformed service to my country."

In 14 markup sessions, the committee changed some provisions that had alarmed Lehman. But Nunn said the most significant provisions of the bill were not changed.

Goldwater, who has strongly supported Weinberger's budget requests, said that public interest aroused by "$600 toilet seats and $3,000 coffee grinders" will help force swift passage of the bill.

The problems that the bill is intended to remedy include military advice to the president watered down to the lowest common denominator of competing Navy, Army, Air Force and Marine interests; military budgets more in tune with service wish lists than strategic imperatives; and military operations marred by poor or nonexistent interservice planning and communication.

The bill would make the chairman of the Joint Chiefs the "principal military adviser" to the defense secretary and president; service chiefs, who both head their branches and sit on the Joint Chiefs, would become less important. The chairman would have a say in the promotions of high-ranking officers within every service.

In the field, the Air Force general in charge of Pacific air forces, for example, would have to report through the Navy admiral in charge of all Pacific forces, rather than directly to Air Force superiors.

Opponents of the bill said that strengthening the chairman threatens to create a "Prussian-style general staff" that could diminish the diversity of military advice the president receives. But Sen. John W. Warner (R-Va.), who opposed the draft bill, said enough amendments were approved in committee to guard against that trend.

While the chairman would be "principal" adviser, each chief is recognized as a "military adviser" whose dissenting opinions the chairman must forward to the defense secretary. The joint staff would serve the chairman and other chiefs, not just the chairman.

The current chiefs were very concerned that they would no longer be able to serve as "acting chairman" when the chairman is out of town; the bill suggests that the vice chairman indeed assume that role, but leaves the final decision to the president and defense secretary.