Edwin McDowell reports on publishing for The New York Times.  LMOST a quarter-century after its original publication, ''Winnie Ille Pu,'' a Latin version of A. A. Milne's ''Winnie the Pooh,'' is back in the nation's bookstores.  Now, as then, the book contains not a single page in English, yet that handicap did not prevent its becoming the only Latin book - and perhaps the only book in any foreign language - ever to become a New York Times best seller.  Published in December 1960, it remained on the Times list for 20 weeks and sold 125,000 copies in 21 printings. 

''Even Caesar never took a country as large as America in two months' time,'' commented The Christian Science Monitor. 

Few books have ever enjoyed so friendly a reception.  A New York Times writer (Lewis Nichols) called it ''the greatest book a dead language has ever known.''  The Chicago Tribune declared that ''it does more to attract interest in Latin than Cicero, Caesar and Virgil combined.''  Time, in a lead review shortly before Christmas, described it as ''a Latinist's delight, the very book that dozens of Americans, possibly even 50, have been waiting for.''  But it added, ''what better gift for the child who has everything?'' 

Within days, however, ''Winnie Ille Pu'' became virtually impossible to find.  A week after publication, the Scribner Book Store posted a sold-out sign in its Fifth Avenue window, saying, ''Editione omne vendita non restant exempla libri de Winnie Ille Pu (latine).''  The publisher, E. P. Dutton, its stock exhausted, ran an ad illustrated with the book jacket drawing of Pooh attired as a Roman centurion, declaring, ''Mea Apologia Winnie Ille Pu.''