A ROCK climb's appeal can depend on motley factors, not least an airy situation, clean porphyry or granite and some technical intrigue. Classic routes, of course, come in any style and standard though the lower the grade the bigger the draw for the greatest flock of climbers. So who has composed Scotland's ultimate rock hit, the climb with real magnetism? And what constitutes its charm?

Glencoe, you might guess, with its scenic and ready access from the techno-industrial belt and the M74, that compact enclave with a wheen of varied climbs should be a likely howff for such an opus. Indubitably. You'd be right.

And the herdsmen of the glen, the Buachaille Etive Mor whose symmetry commands the eye on the fast east descent from Rannoch Moor and guards the snaking pass to Loch Linnhe in the west, again you shrewdly suppose would nurture this rare ornament.

What else, then, but Agag's Groove, the flushed claymore slash across Rannoch Wall seen distinctly from the A82 and the old Jacksonville car park. At a modest V Diff, Agag (named from the mythical giant who trod so carefully) can be climbed by anybody. And going by the retinue pestering his door these days, you might think it's now the intent of everybody.

Glasgow salesman J F (Hamish) Hamilton launched himself on the groove in August, 1936, with teacher Alex Small and Rolls-Royce engineer Alex Anderson. Repelled on that first attack by dampness and the perceived severity of the line, they smartly came back to outflank a rival platoon led by the redoubtable W H (Bill) Murray. Hamish surmounted the crux, an exposed red nose of rock whose steep angle adds sensationally to the route, by removing his sandshoes and advancing high above his comrades, in his woolly socks.

That testing move above the Haven on pitch 3 is now familiar to countless climbers, worldwide. Regardless of technical ability or fitness, most will have marvelled at the bold determination of the original trio. Enticed by that earlier commitment to embark on the now classic Agag venture, the appreciation by modern youth of a past endeavour transcends time and situation.

Agag's Grove is wonderfully sited on a mystic mountain, amid impressive architecture and overlooking the watery moor of Rannoch extending from lonesome King's House Hotel to Schiehallion. Its approach across the River Coupall by Curved Ridge is exploratory and challenging and the atmosphere below the wall as impressive as the climb. Even the retreat from the finish of the route on the exposed and dicey traverse to a cautious escape back down Curved Ridge is quality experience.

But on that dual theme of a fine climb in its own right and the esteem owed by a new generation to the past, I would drift deftly a few metres left of Agag to a bolder (in my estimate) and finer route. January Jigsaw is a mild upgrade at Severe standard and takes a far more direct line up the cliff than its wandering neighbour. From the highly popular ridge scramble opposite, JJ ascends what seems to the uninitiated to be a near-holdless, vertical wall reaching more than 250 feet to the skyline.

The point is not simply the proclivity of the face climb, that it fits its coloured jigsaw pieces up the intimidating Rannoch Wall while Agag hugs a comparatively secure groove. It's in the name. January was not the season to be pushing out a Glencoe rock climb a couple of thousand feet above sea-level. What raises the eyebrow further is the year - 1940. And the climbers; a Cambridge undergraduate and his 27-year-old girlfriend.

Esme Speakman was a tall, slim and striking woman who died recently, aged 83, at her home in Taynuilt, near Oban. Over a dram, a cup of tea and some scones she had baked, we talked there a few years ago about the origin of January Jigsaw, and its creator Henry Iain Ogilvy. The story had a certain poignancy. The woman with the searching look hoped that the relationship with her climbing partner would deepen, but Iain seemed more obsessed with mountains.

They met on a train between Paris and Geneva in the summer of 1939. Both were heading for a season's climbing in the Swiss Alps, then a mecca of the upper and posher middle classes. Esme, the daughter of a naval architect who died in her youth, spoke fluent French. She had climbed with friends in the Swiss Ladies Alpine Club in each of the past four years. Iain, president of the Cambridge University Mountaineering Club and recent designer of its tie, hailed from Dundee and a family not far detached from the Earls of Seafield.

Speakman was polite and reticent but warmed to Ogilvy, a more extrovert character. Esme had moved from England with her mother and lived for a time in Comrie, Perth-shire. She had often visited Scot-land on holidays and took to climbing there regularly. Now a member of the Ladies Scottish Climbing Club, Esme agreed to meet Iain for climbs in one of their favourite haunts, Glencoe.

Later that year, they had four climbing weekends together and on one made a couple of remarkable ascents on Rannoch Wall - Red Slab and Satan's Slit. Both are rated Very Severe and Red Slab in particular reveals Ogilvy to have been a bold and venturesome leader. Speakman, described by acquaintances as a fairly timid rock climber, found Satan's slightly harder, but that may have been the result of nerves and fatigue on the second new route of the day.

They met again in January 1940, once more to climb on the Bauchaille's magnetic red wall, a formidable challenge in the prevailing wintry conditions. Iain started up his most direct line yet, in mist and on snow-covered ledges. Esme told me : ''It was sleeting at times. I really don't remember much about the climb apart from its disagreeableness. It was cold, wet and miserable. Iain took ages to move up and I cried quite often.''

Ogilvy, a double rope tied at his waist, wore a blue beret, plus-fours, a tweed jacket and nailed boots. Esme said she had what Iain called an ''enviable'' anorak. Against the freeze she had fingerless gloves and a polar woolly hat. It was a remarkable achievement and a route which today attracts hordes of climbers, many vibrating gentle on the poorly protected second and steep fourth pitches.

The couple met again a few times later that summer but Esme's expectation of an engagement fizzled out, due mainly she felt to Iain's family. She may have been fantasising. At any rate, Ogilvy was dead by autumn. He fell roped to his cousin, Lucy Robson, on Sgorandubh in the Cairngorms. Both died, Iain from a fractured skull.

The SMC Journal obituary said truly that Scotland had lost one of its finest, most promising young climbers. Others, in hindsight, said Ogilvy had poor judgment. He had sent Esme a token of their summer with the words: ''To Esme, as a reminder of four grand climbing expeditions in the autumn of 1939, with two new routes on September 5, in Glencoe. From Iain.'' Actually it was five in all, and a rare trilogy.

Against the freeze Esme Speakman had fingerless gloves and a polar woolly hat. It was a remarkable achievement on a route which today attracts hordes of climbers