On June 29, the distinguished secretary of defense was transformed suddenly into "Mad- Cap" Weinberger. The ire of the Hon. Caspar W. Weinberger was so aroused by the scribblings of a hitherto obscure journalist named Broder that he unleashed a MIRV-missile of a missive to the editor of The Washington Post. In 1,276 well-chosen words, plus charts, he proved conclusively that said Broder was guilty of "yellow journalism" in questioning the posture the administration had taken toward Congress' efforts to limit the size of next year's military budget.

One would like to believe that the secretary of defense was not diverted from his heavy responsibilities by such petty irritations, and therefore assigned the Broder-bombing mission to some of the Pentagon flacks, otherwise known as Caspar's friendly ghosts.

But the style of the letter was vintage Weinberger, and showed the former Harvard Crimson editor at his finest. "Absurd," "shameful" and "maliciously erroneous" were among the milder adjectives with which he singed the offender.

Along the way, Weinberger also lambasted the congressional budget process with such gusto that he pretty much confirmed the main point of the original column: that he and the president he serves will do all in their power, by hook or by crook, to evade the limits on military spending set in the budget passed by the nation's elected lawmakers.

"I do not worship at the altar of the congressional budget process," Weinberger wrote. "I never have, and the reason is that I understand the importance of enforceable spending ceilings, which the congressional budget process does not provide. What it does provide is elastic, nonbinding spending levels at the start and a process for ratifying appropriations in excess of those levels at the end--a 'Rube Goldberg machine' if there ever was one, as President Reagan has said."

Weinberger's description of the congressional budget process differs from that of the Committee on Economic Development, an organization of 200 leading businessmen. In a report released the same day as Weinberger's letter, the blue-ribbon group, including Weinberger's successor as the Nixon administration budget director and three former Cabinet members, said:

". . . the reforms instituted by the (budget) act have had a major beneficial impact on congressional budget procedures. . . . They have for the first time caused individual members of Congress to take responsibility for the aggregate budgetary outcome of their legislative actions. They have clearly facilitated a more rational and coordinated consideration of budget issues and their relation to economic developments. They have also permitted a more systematic look at budget priorities."

The report conceded that "the early years of the new budget process did not result in the degree of improvement in fiscal disciplines" that had been hoped for, but it noted that Congress has responded by "substantially strengthen(ing) the first budget resolution, giving it close-to- binding force," and clamping down on other spending loopholes. "We strongly support continuation of the basic elements of the present budget process and believe that further strengthening of that process is a vital precondition for sound and effective fiscal and economic policies," the business group concluded.

Weinberger and the Reagan administration are pursuing exactly the opposite course, weakening the congressional budget process where they can and evading it whenever possible.

The day before the secretary's letter was published, Weinberger and his partner, David Stockman, the director of the Office of Management and Budget, sent the Senate Armed Services Committee a midnight revision of the Pentagon's fuel prices and equipment costs. By reestimating the inflation factor for 1984, they found $2.3 billion of unallocated funds--including all the money needed to spare the B1 bomber program from what seemed a certain slowdown. "It is strange that at the 11th hour they managed to come up with it," said Sen. Dan Quayle (R-Ind.), a committee member. It sure was. Had Weinberger and Stockman delivered the estimate earlier, while Congress was considering the budget, as they were repeatedly pressed to do, the information could have been used to reduce the overall spending ceiling for the year-- or to reallocate the money to any program, domestic or military. By coming in when they did, Weinberger and Stockman evaded the congressional budget process.

Their numbers look as suspicious as their timing. Their oil estimate, one nonpartisan congressional staff expert told me, is "terribly optimistic"--about $2 a barrel lower than any other figure extant. The prediction of savings on defense materiel flies in the face of the experience in the first half of 1983, when those costs outran estimates by almost 2 percent, the same specialist said.

The latest incident--like Weinberger's earlier refusal to give the Armed Services Committee the guidance it sought on areas for defense cutbacks--demonstrates this appointed official's contempt for Congress.

It does not matter a whit if Weinberger trashes a reporter. It matters a great deal if he trashes Congress, and gets away with it.