A BOLD step on steep rock can have a touch of the Ron Moodies. It's the last scene in Oliver with Fagin on the mobile arm of Dodger. You mostly fancy the risky endeavour but it gels that a brighter career move might be to review-hoo the situation. Maybe, you think, I'd better think again. The immediate quest is a thin downward chasse, a crablike stride left well above a brutish piece of nature's post-modernist carving - a landing sure to inflict more than cuts, lumps or contusions.

Great Slab on Snowdon's finest cliff, Clogwyn du'r Arddu, is a 600-foot, very severe climb. And here we are already, hardly 20 feet off the deck with a sweaty little bugger of a tango. So a nylon sling and a karabiner are deployed in a crack just above to secure the ropes. This should be a comfort.

But in a fall, the well-devised and hopefully safe pendulum over that primitivist exhibit may end in a fast collision with the big Epstein bust on which my partner, John Hardie, is coolly belayed. Forget Fagin and reviews, the sequence is now urgent and instinctive for aching twinkle toes and a breather is welcome on reaching the long, undercut groove.

North Wales is unique in atmosphere and range of rock. In a fairly tight compass are hundreds of hard, quality routes still augmented on virtually a daily basis by talented, daring and inventive conquistadors, of both sexes, with a honed, competitive edge. They build on a great tradition of Welsh sinew, often driven by the English, Scots and others. And bright, at times brilliant, highly sociable and romantic if later rough and ready characters.

Actually the classic Great Slab is by no means the best of Cloggy, Snowdon's dark cliff, even for its remarkable 1930s era. But it was unravelled by one of the most popular and skilled exponents of the climbing art Britain has known. *Colin Kirkus, an apparently uncomplicated Liverpool insurance clerk, died, aged 32, on a Bomber Command raid on Bremen in 1942.

He rapidly became an ace navigator on volunteer, very hazardous Pathfinder missions. Apart from acting bomb-aimer, he once took control of a Wellington when the pilot was hurt, was involved in a crash landing, a sea-ditching, and had to bale out during an op. His Welsh climbs had been exciting, too, and the legacy of often delicate, sensuous and challenging lines he left commemorate him as long as we rove mountains.

Pilot officer Kirkus was as high a flyer as they come. And he leapt from the shoulders of rock giants like A W Andrews, James Merriman Archer Thomson (to name but four), and Geoffrey Winthrop Young, all academics whose writings reflect not simply their great climbs but their energy and depth of mountain spirit.

In direct descent from Colin came an illustrious Welsh-climbing phalanx of Menlove Edwards, Peter Harding, Joe Brown, Don Whillans, Martin Boyson, John Redhead, Johnny Dawes, Paul Pritchard and many others. It is a rare genealogy with a complexity of outstanding climbs to mark the times.

But here we are under that initial Great Slab groove which Kirkus pioneered with Liverpool-based Graham MacPhee, a Scots dentist of no mean climbing ability himself. The 20-foot groove is almost pristine today but Colin, often slow and awkward but never rattled, faced a sweep of unstable grass on the first encounter. ''It was rather like standing on a roll of carpet - with the the carpet going on unrolling,'' he wrote.

Great Slab on Cloggy's Western Buttress hooked Kirkus on new route-leading. He goes on: ''Cooped up all week in an office, I would long for the next weekend. On a photograph of some cliff I would have all the known routes marked with dotted lines. The blank spaces in between fascinated me. Here was unexplored country . . .''

Six years younger and a contemporary activist, Menlove Edwards once teamed up with Kirkus on Clogwyn's East Buttress. He is a swarthy contrast to Colin's fair climbing complexion. A psychiatrist, homosexual and conscientious objector to WW2, Edwards wrote with wit and deep perception of the sport. Obsessive introspection, perhaps, and later mental illness led to his suicide. Of Colin, who was friendly when others turned away, he had high respect.

It seems ironic that these opposing masks of drama should have held such a common drive and mountain esteem leaving jointly, in terms of classic climbs, so much pleasure for other generations. *Paul Work compared their climbing styles: ''Menlove felt his way up. Colin thought his way up. Both were fascinating to watch. Menlove because I could never see how he did it; Colin because I could and so could he.''

Great Slab meanders away out right by a Babylonian garden, up a delicate 40-foot corner (hard when wet) to a pedestal belay, then diagonally left on cracked slabs to the stunning Cloggy ridge. It views west to Anglesey and the extensive, intricate Gogarth sea cliffs and northerly to the more modern and unlikely North Wales rock star playground, the defunct Dinorwic slate quarries. Just across the Llanberis Pass from Snowdon is spread an array of crags so accessible and of such quality rock a Scot, with all that Scotland can venture, has to gaze on in envy.

Feel the width and texture from Kirkus's smooth and snaking Direct Route on Dinas Mot and Edward's blunt Brant and Nea on Clogwyn y Grochan, all still rated very severe, to the modern technical extremes of Ron Fawcett's Lord of the Flies and Pete Livesey's Right Wall. I hardly dare refer to the Llanberis classic of all time, Joe Brown's Cenotaph Corner, the 120-foot open book E1 high on Dinas Cromlech which strikes even the dispassionate tourist tootling down the pass.

On our last approach there were four parties at the foot in waiting, and by now I should imagine bookings have to be in about five years in advance.

* Hands of a Climber, by Steve Dean, Ernest Press; Welsh Rock, by Trevor Jones and Geoff Milburn, Pic Publications.