Criticism of Pentagon management and of weapons cost overruns is as perennial here as summer humidity. But lately, interest in making the Defense Department more efficient and effective has been unprecedented. For example: a string of recent government reports critical of weapons procurement; high-level recommendations from private business executives on how to save money; suggestions that weapons are not adequately tested before bought; announcements by members of Congress - including notable hawks - that they intend to look for cost causes and possible reforms.
The latest salvo in this spate of activity comes from within the Pentagon itself. An internal audit finds that the Air Force and Navy have been paying prices for aircraft spare parts that have doubled and tripled in just a few years. The armed services and defense contractors are sharply criticized in this finding of the Defense Department's inspector general.
Meeting with Pentagon reporters, Deputy Secretary of Defense Paul W. Thayer Tuesday promised ''fast and immediate'' corrective action.
''I can assure you that this is not going to be treated lightly,'' said Mr. Thayer, former chairman and chief executive of LTV, a major builder of military aircraft. ''We will take whatever action is necessary to stop it and whatever penalties will be necessary to impress upon people that this is not right. . . . If it has to be severe, it will, and it may involve people finding new employment.''
The Reagan administration came into office promising to banish waste, fraud, and abuse from federal government, including the Pentagon - the one agency it intended to beef up substantially. It can point to some gains in this area.
But in the 21/2 years it has been in office, the administration also has learned how difficult it is to change established patterns, especially when they involve entrenched and entangling alliances within the so-called iron triangle: Congress, the military services, and weapons suppliers.
And now it faces a special crunch as the prospect of continued enormous federal deficits and a growing public disenchantment with the intended rearming of America - both of which are reflected in Congress - come up against this week's debate on Capitol Hill over the 1984 Pentagon budget. In the Defense Department itself, these same difficulties are on the minds of Thayer and others who sit on the Defense Resources Board and who, over the next three weeks, will be giving initial shape to the fiscal 1985 defense budget.
The House and Senate Budget Committees would like to spend $13.6 billion less than the President wants for defense in 1984. The rate of increase finally fashioned by Armed Services and Appropriations Committees will be substantially less than the 10 percent sought by the administration.
And in his meeting with reporters, Thayer hinted that Reagan officials will have to propose less for defense in 1985 than planned earlier. ''Some hard decisions'' will have to be made, he said, concerning weapons programs, force structure (divisions, air wings, and carrier battle groups), and readiness accounts (training and supplies).
Thayer's job is not made any easier by recent revelations concerning spare parts costs. These are not small potatoes at the Pentagon, where nuts, bolts, and other relatively mundane items add up to billions of dollars in a single year.
In their six-month investigation, Pentagon auditors examined the prices of 15 ,000 aircraft spare parts and found that 65 percent had risen at least 50 percent in cost between 1980 and 1982. More than a quarter had jumped 500 percent or more. Investigators faulted the parts manufacturers, but also said Navy and Air Force contract officers didn't pay enough attention to such costs and were burdened with paperwork. It was suggested that more auditors be hired, and that any rise of more than 25 percent in 12 months require specific certification that it is ''fair and reasonable.''
Questionable purchasing practices here reflect continuing problems with military procurement, which is now increasing much faster than overall defense spending.
The Reagan-run Pentagon, first under Thayer's predecessor Frank C. Carlucci III and now under the former Navy fighter pilot, has initiated a number of steps to buy military hardware and avoid the kinds of overruns that have become legendary. Navy Secretary John F. Lehman Jr. has cracked down on some offending shipbuilders. The Pentagon has held up $25 million in payments to the Pratt & Whitney Aircraft Corporation (one of those cited in the recent spare parts report) for expenses defense officials consider unallowable.
But the most difficult and important reforms - injecting more competition into major purchases, for example - either have not been taken or are yet to take effect.
''They not only have to be initiated, but they have to be driven down into the organization until they become a way of life,'' said Thayer. ''There's still a lot to be done.''