Secrets that China stole in 1997 about a space radar that can expose submerged submarines could aid it in finding subs from commercial satellites or airplanes, and might also help it hide its own undersea weapons, intelligence experts say.

For two decades, seeking to protect its submarine fleet from such surveillance, the Pentagon has tried to monopolize the radar. When it made its debut in 1978 with surprising powers of discernment, military officials blocked release of satellite photos that showed deep, normally invisible wakes of speeding craft.

Last year, the military had the Government set strict limits on the visual powers of proposed commercial radar satellites. And this year, the Pentagon is fighting a Canadian plan to loft a satellite that would break the new American rules.

Now it turns out, according Federal officials, that an American scientist gave radar secrets to China in 1997, forcibly easing the Pentagon's grip. The implications of this disclosure are unclear, because the size of the breach is unknown publicly and because the secret method is reportedly difficult to put into practice, even after years of study.