BOMBAY, India, Jan. 10 (AP)--Stephen Hawking says his life-threatening disease had given him a renewed reason to live.

"The prospect of a short life made me want to do more. I realized life was good and there was a great deal I wanted to do," Hawking said in a speech January 10 to about 1,000 students, scientists and teachers.

Hawking says he is "happier now than I ever was before my condition was diagnosed."

Hawking said he was 21 when his parents told him he had a motor neuron disease. "They were told I had only two to three years to live. I knew things were pretty bad and didn't want to hear the details," said Hawking, who celebrated his 59th birthday in Bombay on January 8.

Hawking suffers from Lou Gehrig's disease, which causes muscle weakness, paralysis, and impaired speech. The author of "A Brief History of Time" is restricted to a motorized wheelchair equipped with a computer and a voice synthesizer.

"Before I got this disease I was very laid back and bored with life," Hawking said.

He said news of his illness "reduced my expectations to zero," but added that he was "happier now than I ever was before my condition was diagnosed."

Hawking currently holds the Cambridge University post once held by Sir Isaac Newton, and his work on radiation emitted by black holes has been hailed by scientists.

Hawking said he is often asked what career he would have chosen if he was not paralyzed.

"I have thought of becoming a political leader," Hawking said, adding he might have taken a shot at becoming Britain's prime minister.

"But after some thought I feel my work is likely to last longer than his," Hawking said.