Ex-Marine Cpl. Anthony Casamento, a veteran wounded at Guadalcanal, will finally get his congressional medal of Honor on direct orders of Commander-in-Chief Jimmy Carter, just in time for the president to make a dramatic appearance before 2,500 voters at the National Italian-American Foundation dinner here tomorrow night.

The decision to overrule 35 years of refusal by successive secretaries of the Navy by pressure from Carter's White House. Pentagon officials close to Secretary of Defense Harold Brown say privately Brown was "furious" at being bypassed by the White House. They told us Brown was not personally informed until official papers recommending the award had been approved by the president.

This is the latest and one of shabbiest examples of Carter's exploitation of the military for partisan political purposes, in this case wooing the Italian vote. With the presidential campaign still young, the case of Cpl. Casamento -- whose heriosm at Guadalcanal was known all these years but deemed not sufficient for the Medal of Honor -- has cast a shadow of fear inside the Defense Department. It is a fear that President Carter is quite willing to plunder the Pentagon for his reelection.

A far more serious exploitation of the military by the commander-in-chief goes beyond medals to the heart of national security: his effort to rewrite Carter administration history to make hmself invulnerable to Republican charges of incompetence or worse in his stewardship of defense, particularly for canceling the B1 bomber. That reached a peak when, with suspected White House connivance, George Wilson, The Washington Post's highly respected Pentagon correspondent, published a factual story on Aug. 14 about the Stealth aircraft based on a government leak.

Leaks to Wilson and other reporters led to Brown's much-criticized Aug. 22 press conference taking the supersecret wraps off Stealth. He said then that "this alters the military balance significantly," even though nine years of development lie ahead.

The decision to go public came over intense protests from serious military men, worried about Soviet countermeasures. Brown defended it on the curious ground that the leaked stories threatened the integrity of the program and required a public revelation, including predictions of a new aircraft far superior to any B1.

The dubious logic of Brown's explanation, given in the glare of television lights Brown normally excludes from his press conferences, was compounded by Carter himself in an erroneous remark to reporters at Perth Amboy, N.J., Sept. 9.

"The first time the Stealth program was ever revealed" was in early August, Carter said, trying to reinforce his claim that publicizing Stealth was forced on the adminstration by leaks. In fact, Aerospace Daily published the first leak on Stealth July 23, 1976. Since then, at least 10 articles on Stealth have appeared in various journals (it was headline in a June 1979 market research service by Bache Halsey Stuart Shields, the investment firm).

Carter defended Brown's revealation as "legitimate" to "tell the American people the truth." He also clearly saw legitimacy when he summoned the uniformed chiefs of staff to the White House at 2 p.m. Sept. 8 to witness his signing of a military pay bill that he had spent most of his administration trying to kill. That first official appearance of the chiefs in his presence since November 1979 added glitter to the klieg-lit singing ceremony in the White House East Room.

Planning is going forward in the White House for more political exploitation and game-playing with defense in Carter's search for votes. On the same day he signed the pay bill with such fanfare, Carter quietly put his signature on the big defense authorization bill, but not with the joint chiefs present and not under klieg lights. Because the bill contains $5.9 billion more than Carter asked Congress for, it is an indictment by the Democratic Congress of his stewardship. But vetoing it a time of rising public concern about defense was politically impossible.

Carter is now privately trying to persuade his congressional leaders not to send him the defense apropriation bill -- containing the actual funds for next year's defense spending -- until after the election. That would put off a possible veto until a safer time, when public sentiment will not be so important.

A president's use of incumbency to gain reelection is anything but surprising. But this president's use of the Pentagon to advance his political interest is something else, something that is casting a bitter pall over the whole defense establishment.