IT IS NO GREAT trick to make Jimmy Carter out to be sometimes foolish, hypocritical, misleading - even untruthful. More than any recent president I can think of, he sets himself up for cheap shots as well as honest criticism by his pieties, sweeping promises and professions of purity.

What takes a bit of doing is actually to try to understand the complexities of the man, to sort out the engineer from the evangelist, the practicing, ambitious politician from the lay preacher and the true believer. Some day somebody may actually unravel the riddle wrapped in the enigma of Jimmy Carter. But we should not, of course, expect this of Victor Lasky, who himself may be, for all I know, a complicated, thoughtful and subtle fellow in real life. As a writer of contemporary analysis of public affairs, however, he is a stuck needle - vindictive, superficial, tendentious, unprofessional. At the back of his latest book, Jimmy Carter: The Man and the Myth, he lists his "Sources"; for the most part they consist of columns or news stories critical of Carter, together with carefully selected excerpts from the president's own statements or writings. Nowhere is there evidence of an effort to strike a balance, to cite a contrary view, to seek either from Carter or his supporters any off-setting evidence that might present him in a favorable light. The other side of arguments does not interest Victor Lasky.

By now you will have detected my own prejudice. I reveal it without shame because the reader is entitled to know it. To admit to having approached the work of Victor Lasky with something less than an open mind is to admit very little. Nobody that I know approaches his work with an open mind - least of all Mr. Lasky. That's probably what makes his books best sellers, for he does have a faithful following. It is also what makes the reviewing of them - by a nonfollower - no more satisfying than the application of a surgeon general's warning to a pack of cigarettes. The addicts will ignore the warning and inhale pleasurably. Those who have kicked the habit, or never had it, do not need the warning.

So why bother? Partly, as with the surgeon general, it's a matter of obligation, I suppose. And there is always the possibility that some unsuspecting reader, unfamiliar with Lasky's earlier polemics, might mistake his work for serious, substantive, fair-minded analysis. Beyond that, there is a little something for everybody here: reenforcement for the like-minded, and a certain stimulation for those, like myself, who are generally ambivalent, often confused, but genuinely intrigued by a president who Lasky himself describes in his opening sentence as "undoubtedly the most amazing man ever to become President of the United States."

He quickly adds, of course, that Carter is "undoubtedly one of the more inept." If that was to be the burden of Lasky's argument it would at least be worth developing. Inept, awkward, bungling, naive, even occasionally downright incompetent - nobody would argue that the Carter administration has not been all of these things at one time or another. But that is not Lasky's central point. Having declared at the beginning that Carter "lucked into" the presidency, he proceeds to present the picture of a scheming, calculating, deceiving, cold-blooded politician, maneuvering with considerable skill and guile - and astonishing success - out of narrow and parochial obscurity into the presidency of the United States. The focus is not so much on ineptitude as it is on impropriety and hanky-panky of one sort or another on the part of the president and his associates. And the central point of all this is the same central point, indeed the obsession, that pervades Lasky's two previous books. The point is conveyed explicitly in the title of one of them, It Didn't Start With Watergate, and at least implicitly in the other, JFK: The Man and The Myth.

True, it takes Lasky a while this time around to get to his central point. Enroute he rehashes the Bert Lance case, the drug incident involving Dr. Peter Bourne, the idiosyncrasies of brother Billy, and a whole series of alleged "dirty tricks," "indiscretions" and supposed campaign irregularities over the years.

Obviously, if it didn't start with Watergate, it didn't stop with Watergate either."

This, in short, is vintage Lasky. He never tells us exactly what the "it" is that didn't start or stop with Watergate. On the contrary, the point is that Lasky has never found anything unique about President Nixon's conduct of his office. His has always been the "everybody does it" defense; and in this as in his two previous books, he does manage to present a reasonably impressive catalogue of things other presidents have done that in some way resemble some of the ghings that President Nixon did.

But Lasky, of course, can sustain no real analogy between the Carter record and the Nixon record. Indeed, he makes no respectable effort to do so. His bill of particulars against Carter himself includes nothing of a criminal nature. Rather, it consists of unsubstantiated, secondhand, warmed-over allegations by disaffected speech writers, columnists with a well-established antipathy to Carter, and politicians who at one time or another crossed swords with him - people like Lester Maddox, George Wallace and Barry Goldwater.

Nothing more effectively gives Lasky's game away than his heavy-handed condemnation of the Carter foreign policy record. Predictably, Carter is almost wholly to blame for the loss of Iran. For the rest, the best to be said for it is that Lasky, in his zeal, did not even consider the possibility that judgments rendered in late 1978 could, just conceivably, be overtaken by events.

"Carter had hoped to achieve a triple crown in foreign policy by the end of 1978," says Lasky, adding: "But he failed to get Egypt and Israel to sign a peace pact. And he was unable to push through an agreement on strategic arms limitation with the Soviet Union. He did establish normal relations with mainland China. But he tarnished that act by double-crossing Taiwan.... Except for China, for which critics alleged the price was too high, none of the other foreign policy extravaganzas Carter had in mind worked."

So much for Victor Lasky's prescience. Leaving aside that Carter did achieve the Egyptian-Israeli peace treaty early this year, as well as the SALT agreement, Lasky dismisses the Panama Canal treaty as something that should have been a cinch and that Carter nearly bungled.He ignores Carter's victory in Congress in the lifting of the Turkish arms embargo, and a similar hard-won triumph - whatever one may think of it - on the question of selling military aircraft to Egypt and Saudi Arabia. Right or wrong, this was central to the whole Camp David strategy as Carter saw it, and he prevailed.

But these are not matters that interest Lasky. In this book, as in the earlier ones, the systematic denigration of Jimmy Carter (or Lyndon Johnson or John F. Kennedy) would seem to have no more serious purpose than the exoneration, by tortured comparision, of Richard Nixon. It is in a sense a vulgar piece of work - figuratively, and even occasionally literally.

At the conclusion there is an odd two-paragraph "Personal Note" in which Lasky feels compelled to report that he did talk briefly to Carter at a White House reception at the end of 1978. The president looked tired and aged, Lasky reports, but "Even though he knew that this book was in the works, he could not have been nicer. "It's a great honor to have you in this house, Mr. Lasky," he said.... The next day, it was announced that he was suffering from a painful anal affliction."

On that strange note, Jimmy Carter: The Man and The Myth comes to a merciful and, you might say, appropriate close; you will have to judge its relevance for yourself. My own theory - and it is no more than that - is that the president may have had some familiarity with Victor Lasky's earlier books and, accordingly, some sense of what "was in the works." In that case, the "affliction," as distinct from the need to mention it, would not be all that hard to understand. CAPTION: Illustration, no caption, by Allen Carroll