Washington — Defense Secretary Caspar W. Weinberger said recently he ''wouldn't dream'' of overruling the commander who insisted on barring the news media from the early days of the US invasion of Grenada.
In Lebanon a few weeks later, the controversial decision to attack Syrian forces with vulnerable carrier-based aircraft - two of which were lost - instead of the battleship New Jersey was left up to the admiral in charge of the Navy task force there.
The trend in the Reagan administration has been to move away from what some have criticized as the ''micro-management'' of military operations by the Pentagon's civilian overseers. Now, under controversial legislation already passed by the House and being considered by the Senate, Pentagon civilians could be turning even more control over to the military.
This has some observers worried that the United States may be headed for a ''general staff'' or ''supreme commander'' approach to military management. And as the debate grows, even Mr. Weinberger warns against ''tinkering with . . . an area of such extreme sensitivity under the Constitution as civilian control of the armed forces.''
The issue focuses on the five members of the Joint Chiefs of Staff - the top officers from the four branches of the armed forces and a chairman - who have two essential tasks: to head their branch of the service and (with a staff of 400) to provide the best possible professional military advice to the nation's elected leadership.
Critics say this ''two-hat'' system ensures a built-in conflict between service rivalry and the broader view necessary to shape national-security policy. The result, according to many observers, is watered-down advice by joint-chiefs consensus that often is less than helpful.
''We're dealing with a system that's encrusted over time,'' Rep. Les Aspin (D) of Wisconsin, a member of the House Armed Services Committee, said the other day.
A House-passed bill now under Senate consideration could affect the greatest changes in this system since the National Security Act of 1947, certainly since the act was last amended 25 years ago.
Under this proposal, the role of the chairman of the Joint Chiefs would be strengthened considerably. The JCS chairman would become a formal member of the National Security Council, and, therefore, an equal on the NSC to the secretary of defense. He would be able to offer military advice to the secretary of defense and the President on his own without having to consult with the other JCS members.
The JCS chairman would pass judgment on all promotions to three- and four-star status, and he would have more power to fill the JCS staff. The 400 -person limit on the staff would be lifted. The current three-year limit on Joint Staff assignments would be lengthened to four years, and reassignment could be made after two years instead of the present three.
Most controversial is the provision that inserts the JCS chairman into the military chain of command. At present, orders to operational combat commanders are merely passed along by the JCS from the President and secretary of defense. If approved, the new measure could allow the JCS chairman to supervise combat commanders himself.
The legislation follows several years of debate which have seen former JCS members and other analysts urging that the role of chairman be strengthened to provide better military advice and to streamline JCS operations. In some ways, it merely confirms in law what has come to exist in practice. The JCS chairman, for example, aleady sits in on most NSC meetings.
Some see it as more far-reaching, however. They are not so much worried about what the current Joint Chiefs might do, they say, but what could happen under future administrations.
''This legislation would drastically increase the role of the chairman of the JCS,'' Jeffrey Barlow of the National Institute for Public Policy, who is just completing a book on the JCS, told a Heritage Foundation seminar last week. ''It would make the JCS chairman in effect a single chief of staff, who would be in de facto command of operational forces.''
''It strengthens the chairman, not at the expense of the parochial interests of the four services, but at the expense of the secretary of defense and that's a big mistake,'' said former senior Pentagon official John Kester.
Others say that strengthening the JCS chairman - particularly in directing the staff - will help cut through those competitive interservice issues that cause the most rivalry: budgets, unified commands, and the roles and missions of the services.
''It will provide better advice on these toughest of issues,'' said Richard Steadman, who directed the 1978 study on military command structure that prompted the current debate.
The Reagan administration favors adding the JCS chairman as a link in the chain of command and strengthening the joint staff. But it is wary of proceeding much further. Having the JCS chairman be a member of the NSC, Defense Department general counsel William H. Taft IV warned the House Armed Services Committee, ''would blur the distinction of the basic precept of civilian control over military activities.''
The current JCS chairman, Gen. John W. Vessey Jr., on the other hand, told the Senate Armed Services Committee such a move would have ''some clear benefits'' in NSC deliberations dealing with US military capability and preparedness as well as the deployment of combat forces.
In any case, said General Vessey, ''The ultimate test is the ability to move from peace to war and to fight the war to a successful conclusion, should deterrence fail.''