ONCE A YEAR Scotland's capital experiences an amazing transformation, more striking in its way--and certainly more fun--than that well-remembered son of Edinburgh's Jekyll into Hyde. It is not so much the official and famous Edinburgh International Festival that brings this about, as what is affectionately known as the "Fringe," an alternative festival, an extraordinarily multitudinous and diverse assortment of performances and productions, that clothes a normally somber city in carnival gear. There are poets in the pubs, singers on the streets, dancers in the parks. There are amateurs, part-timers, aspiring and established professionals. And there is a book festival.

Scotland's literary scene is often lively, with a fierce sense of the need for Scottish writing, Scottish publishing and Scottish book-buying. The liveliness can at times be pugnacious. There's a continuing argument, decades in duration, about the Scottish literary psyche which can get a bit punchdrunk at times, with a lot of hitting out at allies as well as enemies. The latter range from the "Sassenachs" (or southerners) to the internal contradictions of the Scottish tradition. Last year a gathering to discuss the predicament of the Scottish writer failed dismally to do justice to either the quality or the awareness of contemporary writing in Scotland. Most writers would admit to a predicament of some kind or other. The insistence that Scottish writers have their own special brand has become almost as distinctive a mark of identification as the kilt.

But the book festival forgets, almost, the predicament and gets on with the business of making books and their makers appealing. It is the brainchild of the National Book League and the Scottish Arts Council, with committed support from Scottish publishers. It competes with a breathtaking array of rival attractions--all around the city seethes with concerts, drama, dance, opera, exhibitions and the attendant openings, private views and parties. But it is right to hold the book festival now, as the film festival and the jazz festival have also discovered, to cash in on a packed population of culture seekers and the electric atmosphere that will fade when in mid-September the shows close and the sea mists seep up from the Firth of Forth.

The book festival is housed under marquees ranged in Edinburgh's most impressive square. The fact that a literary circus is taking place under the dignified and ever so slightly severe neoclassical proportions of the city's renowned Georgian New Town makes it all the more fun. Edinburgh has not quite outgrown its Calvinist reputation, and there is a lingering suspicion of books other than the Bible and "improving literature." This goes hand in hand with Edinburgh's great tradition as a literary city--just another one of those internal contradictions.

The problem is to present books and all concerned with them as performers. The program is tempting and thoroughly mixed in brow level. There are "meet the author" sessions-- P.D. James and Ruth Rendell, John Updike, Margaret Drabble, William Boyd and others--where audiences are invited to participate in discussions with the authors, and the atmosphere is pleasantly informal. There are entertainments--poetry and song ranging from Sorley Maclean's gentle Gaelic to the mesmeric drama of a group of musicians from Rajasthan, the latter in honor of the Indian theme which is a book festival focus this year. There are talks on horror fiction, drama, adventure fiction, women's writing, and David Daiches on Scotch whiskey-- "with refreshments." And there are two sessions every day for children.

In fact for the kids it's a party, aided by the BBC's exhibition "60 Years of Children's Broadcasting," full of nostalgia for those, like myself, who grew up with the stories and personalities of "Children's Hour," much enhanced by a reconstructed 1950s living room graced by a good old-fashioned wireless. A damp lunchtime--the weather has broken after weeks of sunshine, and I'm sporting a rare north-of-the-border tan--showed no diminishment of the party spirit. Children with balloons and paper hats boosted an infectious air of action and excitement. Things were happening, words, music and of course the flickering TV screen, and the large number of visitors, children and adults, radiated expectation. It was nice to feel that this was all about books and storytelling.

The authors perform, the audience participates, the discussions and the signings continue apace--but what about the books themselves? The displays are tempting--there's a lot of pleasure in books that look good. Music and cookery, sport and poetry, fiction and fantasy, comedy and criticism, with a post- a-book service so you can dispatch all your Christmas presents on the spot. Prominent is the Scottish publishers display. We're a small country, population 5 million, yet we manage to sustain at least 26 Scottish-based publishers. The books produced are mainly of Scottish interest, with much tourist bait: Scottish poetry, Scottish fiction, Scottish wildlife, Scottish mountains, Scottish monsters, Scottish food, Scottish places and Scottish personalities. But perhaps most of all Scotland's past. For both native and visitor the magnetism of historic Scotland sustains its strength. And to set out to explore why would take us back to those predicaments again. Suffice it to say that, as all Scotland's foremost writers have discovered, if you live here you can't get away from it, and if you're passing through it's hard to resist it. And if it helps Scottish publishers to sell books, who's complaining?

Take a stroll out of the book festival tents in Charlotte Square and into Princes Street. There's the castle splendidly overlooking the scene and the inimitable skyline of the Old Town tumbling down the incline that was the backbone of the original city. Turn your back on the castle and walk north through the new town, and suddenly there's a spectacular glimpse of the firth and the hills of Fife beyond. No wonder the city has inspired poets and storytellers. And if a tumbler suddenly cartwheels before you, or you catch the sound of bagpipes on the wind, it's all part of the message that books don't have to be too serious a business.