WHEN ARTHUR M. SCHLESINGER JR. came out last year with Robert Kennedy and His Times, Midge Decter wrote in Commentary magazine: "Never may so formidable a mind and so accomplished a pen have produced so unsubtle an electioneering pamphlet." Her thesis was that while Teddy barely figures in the book, "Schlesinger gives us clearly to understand that . . . the Kennedys are interchangeable." But a hardback selling for $19.95 can hardly qualify as an electioneering pamphlet. Ballatine's $3.95 paperback that came out a couple of months ago may reach the voting rabble, so it's time for a re-view.

Schlesinger's efforts as a pro-Kennedy propagandist are more than cancelled out by his instincts as a historian. Whatever partisan intentions he may have had, he has produced a book that is luxuriant with stuff that could sink the Kennedy legend.

The picture we get of President Kennedy during his buildup of U.S. troops in Vietnam (from 600 when he went in to 16,000 at the time of his assassination) is of a leader completely befuddled, sometimes almost incoherent in his inability to choose between conscience and political expediency.

And wait till you read how Kennedy chose his Cabinet. Would you believe he appointed Douglas Dillion, a Wall Street Republican, to be treasury secretary partly as a favor to columnist Joe Alsop? No kidding. Would you believe that one conversation with another Wall Street big-shot, Robert Lovett, was enough to convince him to hire Dean Rusk as secretary of state, though Kennedy knew absolutely nothing about Rusk? And then he kept Rusk in the job even after it became clear that he couldn't take pressure. According to Robert Kennedy, Rusk just fell apart during the Cuban missile crisis -- "Rusk had a virtually complete breakdown mentally and physically."

As for Attorney General Kennedy -- once the vigorous admirer of Herbert Hoover and Joe McCarthy -- we find him falling under the spell of General Maxwell Taylor's kookaboo Cold War plots -- "organizational fantasies," Schlesinger calls them, a grandiose marshalling of the whole government for a global assault on communism, an assault that would emphasize counterinsurgency. Green Berets, here we come!

Kennedy courage in political matters does not seem exactly overwhelming. President Kennedy reportedly hated General Curtis LeMay so much that after every conversation with him Kennedy had "a sort of fit." Fits or no fits, Kennedy not only kept LeMay around but promoted him to please Congressional right-wingers.

Attorney General Kennedy admitted privately that J. Edgar Hoover was "psycho" and "senile" and that the FBI under Hoover was " a very dangerous organization." But, he explained, he and his brother didn't want to fire Hoover because "the president had won by such a narrow margin" and they didn't want to give the right wing something to hit them with.

Excuses based on expediency are bad enough. But another explanation might be that Bobby had his own dark side. After all, Schlesinger points out, as attorney general Bobby authorized wiretaps on newspapermen, on lawyers, on bureaucrats and on Dr. Martin Luther King Jr. and associates -- but not once did he authorize a wiretap on racketeers.

As for the president's attitude toward big business, Kennedy did buck Big Steel momentarily, but he was so shocked by his own show of spunk and so fearful of the corporate passions such action might arouse that "his policy toward business thereafter," writes Schlesinger, "was one of mild appeasement."

So much for Camelot.

Donald L. Barlett and James B. Steele's Empire: The Life, Legend and Madness of Howard Hughes (Norton, $15.95) is the best big business-big government biography of 1979, maybe of the decade, and anybody who disputes that judgment just doesn't know great capitalistic pornography when he/she reads it. Hughes appears to be a kind of second cousin to Mel Brooks' Frankenstein. He was a monstrous weirdo who lived off of codeine, chocolate bars, hokey publicity and government largesse. The CIA and CAB and Pentagon helped put the monster together. Hughes seems to have spent half his life watching old movies and thinking up better ways to fight germs (handle everything through six or seven thicknesses of Kleenex). In his last years he preferred wearing only a shirt or going entirely naked. He was mad, mad, mad.

So how come he was so rich and successful? Well, rich he certainly was, but as Barlett and Steele prove in a most dramatic fashion, Howard Hughes was in fact anything but a success. At Trans World Airlines, in Hollywood, in Las Vegas, in defense contracting, in just about every business activity that he occupied himself with for long, the ultimate results were disastrous.

But the government needed him as a front; it needed his Hughes Aircraft Co. and his Glomar II, and some of our more notable political crooks enjoyed his gifts. So Howard Hughes the empty legend was permitted to flourish for decades -- sustained by a spooky network of aides and by a corrupt government. TheInternal Revenue Service, for example, solemnly approved the creation of the Howard Hughes Medical Institute as a "charity to benefit all mankind," though it was obviously multimillion-dollar tax dodge aimed primarily at keeping the Hughes Aircraft Co. financially afloat.

Then, his usefulness over, Hughes was swindled of his corporate power and killed by neglect. An ugly, brutal, fascinating story.

Dan Morgan's Merchants of Grain (Viking, $14.95) ought to get some special prize from the book-publishing industry. Just when it seemed that the best-seller list was virtually reserved for books about exorcising haunted houses and jogging and gossip of various sorts, Morgan came along with one of those immensely imortant but immensely dull topics -- the international grain market -- and, through sheer grace of style and mastery of subject, turned it into an adventure story that sold. Talk about cabals, why, OPEC is a sprawling, inchoate gang of amateurs compared to the poeple who control the world's grain supply: five companies (seven families) who reap their riches with a ruthlessness and secrecy that is pretty frightening -- made all the more frightening by the fact that our agribusiness leaders and farm bureaucrats work hand-in-hand with them. Even if our federal politicans wanted to cut off grain to Iran, the mysterious Fribourgs, Hirsches, Borns, Cargills, MacMillans, Louis-Dreyfuses and Andres might very easily undermine our best efforts at revenge. The United States is the world's greatest grain producer and exporter, but, as Morgan indicates, that does not mean we know how to use our clout.

If the hungry hordes of illegal aliens coming this way make you nervous and upset, a superb antacid has just arrived in the form of The Golden Door: International Migration, Mexico and the United States by Paul and Anne Ehrlich and Loy Bilderback (Ballantine hardcover, $12.95). It shows the problem to be, if not open to solution, at least open to a great deal of sympathy. Mexico City has grown "by over four million people -- about the combined population of Chicago, Cleveland and Cincinnati -- in just seven years," and hundreds of thousands of its residents "make their livelihood by 'mining' the refuse heaps and garbage dumps on the edge of town." Tired of that existence, one out of every seven in the Mexican work force has illegally come to the United States. Do we want them? Probably not. But before getting too angry with the Mexicans, bear in mind that they are finally trying to do something about their population by a heavy emphasis on birth control, and that more Mexican blood might put some zip into our politics. The history of Mexico's politics this century -- wrapped up here in two perfect chapters -- read like one of Hollywood's wilder adventure stories. If Ronald Reagan, why not Pancho Villa?

One of the injustices of the year was the failure of Confessions of a Muckraker by Jack Anderson and James Boyd (Random House, $12.95) to become a best seller. More dramatically and more persuasively than any other book you're likely to find, Confessions reveals the cold-welded relationship of journalism and politics in Washington. Anderson does it (with the faultless writing of Boyd) by evoking the career of his boss of many years, Drew Pearson. God, what a gutsy marvel that guy was! Even when he perpetrated high-level blackmail he did it with a fine flourish. When General Douglas MacArthur hit Pearson with a $1,750,000 libel suit, Pearson hunted up MacArthur's Eurasian mistress -- "whom he [MacArthur] had imported from the Philippines with promises of undying love," promises that were growing cold -- and sweet-talked her into releasing a packet of MacArthur's love letters. MacArthur quickly surrendered. At which point we come to the populist denouement: "All promises were kept. The dancer from Shanghai was taken to the Middle West by Drew's brother, Leon, and established as the proprietress of a successful beauty parlor."

While Pearson exposed the usually unsavory but sometimes hilarious lies of Joe McCarthy ("I carry 10 pounds of shrapnel in this leg"), the cupidity of Eisenhower, the dangerous mental imbalances of James Forrestal, the wretched corruption of such politicians as J. Parnell Thomas (whom Pearson packed off to jail), he often had little support from the rest of the press and sometimes had to contend with its outright opposition. Publishers frequently banned his column, and during his anti-McCarthy crusade advertisers virtually drove him off the air.

Pearson's usefulness as a muckraker was in his willingness to violate all the textbook canons of proper journalistic conduct. He was anything but objective. He often violated good taste and sometimes violated ethics. He didn't merely report; he took sides -- always. And almost always the people's side. He immersed himself in what he wrote about, "The life role he most enjoyed," write Anderson/Boyd, was "that of maximum politico -- part intelligence sleuth, part commentator, part lobbyist, part propagandist, part consipirator, part caucusmaster."

Although many of Pearson's best stories were turned up by Anderson and although in his last years Pearson would have been in bad shape without the support of his young partner, it was the passion of Pearson that made the column what it was and what it would never again be -- perhaps partly because of changing times -- after his death in 1969. Anderson was too much of a square, too much the orthodox journalist, to continue the Pearson tradition, and he is honest enough to admit it here. But they are a unique team, and this book is a marvelous memorial to their teamwork.