By his own account, Barry R. Clausen has infiltrated radical environmental groups, staked out logging protests and helped bust a drug ring. He has testified before Congress about a rising tide of eco-terror, has been quoted scores of times in the national and international press and has appeared, he reckons, on 150 talk radio shows. But the Federal Bureau of Investigation and many other law enforcers don't see any sign of the surging eco-terror Mr. Clausen describes. Pressed, he acknowledges that his list of documented terror incidents includes graffiti and pie-throwings. Even some supporters say he sometimes stretches the truth.