By Alan Baldwin

LONDON (Reuters) - At 77-years-old, Jackie Stewart has a new challenge that he ranks among the biggest of his life.

The Scot, who raced through one of Formula One's deadliest eras and won three world championships, and who campaigned for driver safety when others mocked and blocked, says he has his work cut out this time.

Stewart is putting 1 million pounds ($1.29 million) into a new global charity he has set up to accelerate research into finding a cure for dementia, an illness his wife Helen was diagnosed with two years ago.

"It’s not the same as motor racing safety. That was a tough enough task. But this one’s tougher," he told Reuters in an interview.

"It's difficult enough finding money to start a Formula One team that we did, Paul (his son) and I. This is a much bigger task. And it’s bigger money in the long run. So I’ve got to work awfully hard on this.

"Obviously it’s a shock. And it’s a different kind of shock," added the man whose life has been marked by profound dyslexia and the deaths of some of his closest friends and rivals on the racetrack.

"I’ve been through a lot of unhappy times with everybody that I have close to me, really all of them died – if you think of Jimmy (Clark) and Jochen (Rindt) and Francois (Cevert), Jo Bonnier. A long list... and I haven’t had anything like that for an awfully long time."

Stewart, as always, will be at Silverstone for the British Grand Prix this weekend, and so too will the woman he has been married to for 54 years.

Once a familiar face on the pitwall, and on the movie screen in Roman Polanski's 1972 Monaco documentary 'Weekend of a Champion,' she timed laps to fractions of a second but now forgets to wear a watch.

"She could take down 26 racing cars on the same track at the same time on one single stopwatch. As did Betty Hill, Pat Surtees, Bruce McLaren’s wife, Jochen Rindt’s Nina," said Stewart.

"It was Nora Tyrrell and Helen Stewart timing for the whole team, but at the same time in the race doing a lap chart for 26 cars. Here’s the sharpness, a laser brain ... and then suddenly not remembering the most simple thing."

Stewart said his charity, called 'Race against Dementia' www.raceagainstdementia.com), would aim to find and fund original thinkers who might come up with solutions in a way motor racing people would understand.

"I want to find an Adrian Newey in Sri Lanka, China, India, America or the UK," he said, referring to Formula One's standout designer whose cars have won titles for three different teams.

"If we can find around the world those sort of people, I have to believe we are going to find a cure for this or a preventive medicine for it."

(Editing by Peter Rutherford)