THE first three years in climbing, they say, are the most dangerous. In Sir Chris Bonington's case, the next 27 were not exactly a romp in the garden. Emerging only slightly scathed at times from three decades of mountaineering - from the first British conquest of the Eigerwand to Everest Direct and further - is a remarkable achievement. Viewing the collateral casualty rate along the way, it may seem awesome.

Chris, as he'll continue to be known in the mildly anarchical mountain world, could be aptly described as off-the-wall, the callow teenager ill-clad for winter, being avalanched on Snowdon. A plummy accent inquiring at a sullen Creagh Dhu MC fry-up for a climbing partner. Those fretful first ascents of icy Agag's Groove and Raven's Gully in Glencoe. And early, harrowing frights in the Alps, again with Hamish MacInnes. And others. It just had to end in tears.

Yet here he is, 63 years young and large as life, lecturing in Perth tonight on 30 wondrous years of mountaineering around the world. It is a lone appearance in Scotland among a dozen British venues, but hardly a gig he'd miss. Bonington has a rooted affection for the far north. His portal to climbing, after all, was a picture book of Scottish mountains. Those blue remembered hills ensnared him for good.

There's nothing remotely valedictory about his slide autobioptic, he hastens to explain. ''I still love climbing, absolutely,'' he enthuses. ''I'll hopefully go on until I'm 80.'' As evidence of an indestructible fibre, he cites an imminent venture with Robin Knox-Johnstone into the northern fjords of Greenland. And a Big Wall assault there with a more youthful climbing partner. He has not had this sort of experience, he reminds us, since he topped the Central Tower of Paine in Patagonia with Don Whillans in 1963. About the only concession he allows is the wry: ''Heaving a big sack around at altitude these days is a bit of an effort. But it's better than slumping in an armchair.'' An audience with ''Bonners'' will note few slumps and fewer chairs in an audio-visual travelogue that makes Michael Palin look like a day-tripper. And the hirsute, near-6ft charmer of a man can be highly amusing

too.

Apart from Doug Scott, still going strong, Bonington's view from the heights of a long and exciting climbing career is unique in the UK. Where others of outstanding ability, such as Mick Burke, Dougal Haston, Peter Boardman, Joe Tasker, Nick Escourt, Paul Nunn, et al have succumbed to the mountains' deadly siren call, Christian soldiers on, his fitness, brio, and marriage still very much intact. And two grown-up sons besides. Just how has he kept it all together? Mostly, he readily concedes, with a lot of luck.

You wonder about the selfish factor, not the personal risks and fears but the deeper, uninvited fears of kith and kin. And not just for the moment, but over years of bold adventuring. ''It can be incredibly difficult,'' he admits. ''I am a son, a partner, and a father, so I have that responsibility in three directions.''

HE adds: ''I think some people are attracted to games with an element of danger. The individual needs to experience this and develop to the full. Climbing, remember, is only one such sport. There are comparatively more fatalities, you know, among horse riders. People must really make up their own minds about their commitment. It's not for the outside world to interfere.''

Bonington seems fairly complacent about another controversial concern of the moment. Of the rent-a-guide, up Everest at #40,000 a go, he says simply: ''I would not envy the quality of the client's experience, but guiding has always been an aspect of mountaineering. I think we have to expect that Everest will become a gigantic Mont Blanc with its attendant commercialism, accidents, and tragedies.''

He appears more concerned about a recent ruling in the High Court in London against the British professional guide Dave ''Smiler'' Cuthbertson who fell on a steep icefield of the Tour Ronde in France, pulling his client to his death.

Though the judge found Smiler negligent, largely on the expert evidence of the highly experienced Scots guide and Glenmore Lodge instructor, Allen Fyffe, Cuthbertson's professional association later vindicated him. Chris says he fully appreciates Allen's forceful evidence, which favoured the claim made by the widow for her young son's future, but feels the judgment lays too much confidence in hard and fast climbing rules. In this case the requirement not for one but two ice anchors at the belay point.

''Climbing is just not like that,'' he insists. ''A guide cannot give an utter guarantee that this client will be entirely safe. It is a fact of the sport that risks are faced. While the judge was clearly looking for what might be a definite procedure, climbing has few definite rules. It depends on circumstances.''

Though the judge himself suggested that the finding should not be considered a precedent for future mountain accident hearings, the implications for those dealing in high risk sports are evident. ''I think that the clearing of Smiler by his peers will balance the court ruling. Certainly lessons have been learned by the guides' association.''

The doyen of British climbing, Christian John Storey Bonington, retains an indefatigable interest in the history and progress of the sport and is quick to contest the modern trend to place bolt protection on cliffs against the established ethic.

Very bold traditional climbs on igneous or limestone cliffs in Britain and the Alps are today being retro-bolted by a new generation seeking quicker, cleaner, safer climbs. Chris accepts that the youth of today often climbs near-holdless faces at a mind-blowing standard where the security of occasional bolted protection is essential.

But the failure of many to meet the standards set by their predecessors on traditional cliffs, he says, is disturbing. He calls for a more

pro-active response against the trend, what he terms more ''evangelising'' in favour of the past ethos.

If you ask the old master if he might eventually consider a more recreational life, his response is at first a surprise. ''My wife, Wendy, has discovered a passion as great as my climbing,'' he reveals. ''She has taken to golf in a big way. She plays with the wife of a climbing friend of mine. I think we might all go on a golfing holiday soon. The girls can golf. We'll go climbing.''