IT'S SPRINGTIME for Hitler on the newsstands. And editors, suddenly faced with an embarrassment of Third Reich riches, are scrambling to decide which is the better story: The discovery of 60 diaries said to have been handwritten by the Fu hrer himself; or the growing suspicion that the black, leather-bound volumes are a stupendous fraud.

When Stern, a popular West German magazine, announced last week that it had obtained the diaries, it backed its claim with endorsements from Cambridge historian Hugh Trevor-Roper and handwriting expert Ordway Hilton. Readers braced for an orgy of Reichsploitation in the press. But Hilton later hedged; yesterday Trevor-Roper waffled at a Stern press conference, calling for further study; and a widening chorus of critics is crying hoax.

None of which surprises veteran author Clifford Irving, convicted in 1972 of forging a bogus autobiography of reclusive billionaire Howard Hughes.

"It would be entirely possible for someone intelligent, gifted and artistic" to deceive press and experts alike, Irving said yesterday from the remote Mexican hamlet 170 miles from Mexico City where he is "working on a novel set in wartime Germany." All it would take is a "skilled forger" willing to "immerse him or herself in the handwriting, character, syntax and spirit of another person," and "to study all the abnormalities and changes that are exhibited in the handwriting over time."

After all, the Hughes papers fooled Osborn Associates, a noted New York handwriting-analysis firm that authenticated the fakes. "And I was just an amateur!" But then, Irving said, "experts tend to drift with the tides. Nine out of 10 times, they come up with the judgments you expected" because "they're hired by people who want an affirmative answer."

Fortunately, he said, "both Hughes and I studied penmanship in the same American public school system where everybody is taught to write alike. He never lost his grammar-school penmanship lessons." So within "a matter of months, I could write a 10-page letter," taking only twice as long as it would have taken to write in his own hand.

The vast bulk of the purported Hitler diaries--60 books of 75 to 100 pages each--is no guarantee of accuracy, Irving said. "Once you have the mood, you can go on forever. I know that from personal experience. I could write 60 volumes of Howard Hughes autobiography and they would pass. Once you do one page, you can do 20. Once you do 20, you can do a book."

Although only one person could do the actual writing ("to avoid discrepancies"), Irving says the faker would probably have one or two accomplices. For one thing, there's the awesome volume of research required to create a narrative that is historically plausible yet "racier and more controversial" than existing sources.

Then there are the technical demands of fabricating a credible document. "Let me write a little scenario for you," Irving said. "Somebody finds, say, 100 old unused diaries dating from the '30s, and 50 bottles of old Wehrmacht ink. Maybe that's what started it." But the ink would then have to be artificially aged into the paper. "That kind of expertise is definitely available. They know how to age canvas--even a signature on a print." The hoaxer would also need a confederate, he said, "because it's lonely." Under the pressure of such a secret, "you would have to ask someone from time to time, 'Am I crazy?' "

But Irving stressed that he had no direct knowledge of the diary flap. "I'm so removed from it all down here in the wilds of central Mexico," he said. "The whole affair has an aura of unreality."

This week, readers may draw the same conclusion by comparing the diary coverage in the current issues of Time and Newsweek.

Time devotes its cover to the pouty puss of Nastassia "Exposed" Kinski and "Hot Faces from Europe," giving the Fu hrer only a three-word notice in the index. Yet back on Page 42, Time's 1,200-odd words on the diary disclosure are definitely bullish on authenticity, employing locutions such as "Hitler's scribblings" and "Hitler wrote," without the customary caveats, and stating that the discovery "could prove immensely valuable to historians." Fewer than 100 words are devoted to skeptical remarks by two West German historians.

Newsweek gives Adolf the cover ("Special Report: Hitler's Secret Diaries" in Nazi color scheme--red, white and black) but asks immediately, "Are They Genuine?" And it spends half of the 11-page spread in an orgy of dubiety, profiling one expert who believes the document genuine, but several more who don't. ("The new find," says Prof. Gerhard Ludwig Weinberg of the University of North Carolina, "should be read with a giant saltshaker at hand.") And Newsweek explains how its editors were originally interested in purchasing the rights to the diaries, but ultimately demurred "principally because they wanted more systematic and authoritative authentication and because they disagreed with Stern's plan to publish installments of the diaries in small batches" over as many as 18 months.

The authenticity squabble should be good for tens of thousands more words before it runs its course. After all, if there's anything more salable than the swastika, it's a venerable pundit with not just egg, but an entire omelet on his face. As Clifford Irving wrote in "Fake," his 1969 book about legendary art forger Elmyr de Hory, "All the world loves to see the experts and the Establishment made a fool of, and everyone likes to feel that those who set themselves up as experts are really just as gullible as anyone else."