No one, it seems, is more zealous about cults these days than an excultist. Three years ago Steve Hassan, now 25, was working 20-hour days, seven days a week for the Rev. Sun Moon's Unification Church. He was in command of a fund-raising team of young men and women who canvassed Baltimore streets, raising about $35,000 in eight weeks that he says he wired to a bank account in New York.

Now working toward a bachelor's degree at Boston University, Hassan is starting a group called Ex-Members Against Moon that he hopes will alert the world to what he perceives as a fascist organization operating under the guise of religion. His hatred of cults extends beyond Moon's organization, too: he is also helping organize a Washington rally and prayer vigil to mark the first anniversary of the suicides and murder in Guyana November 18 and 19.

"Our involvement with the Moonies was a traumatic experience that most of us want to forget," Hassan wrote in his first newsletter to former colleagues who, like him, left the Moon fold. "But we bear powerful witness to the reality of the inherent dangers of mind control technology. We should not belittle our knowledge and experience or fall victim to the stigma of being labeled ex-cult members or members of the anticult cult. We are the real experts ."

Hassan came by his expertise six years ago while eating lunch at Queens College. He was feeling down because he and his girlfriend had parted ways. By invitation he attended a lecture with other young people whom he eventually learned were followers of the Rev. Sun Myung Moon, a South Korean evangelist with extensive property holdings in the United States.

Over a period of 27 months Hassan says he rose through the ranks of the Moonies until, weary from panhandling on Baltimore's streets, he fell asleep at the whell of a van on the Baltimore beltway and veered into oncoming traffic. While recovering in Long Island at his home, his parents surprised him by taking away his crutches and springing a "deprogramming team" on him.

"I seriously thought," he told free-lance writer Jeff Stein recently, "of snapping my father's neck."

But four days later he renounced his association with Moon. The massacre at Guyana brought to the surface his interest in -- and now hatred of -- cults. Hassan echoes the theme of a recently published book by ex-Moonie Chris Edwards that Moonie violence will increase inproportion to Moon's failed messianic hopes.

Although Hassan says Congress and the FBI are reluctant to investigate any movement that can be called a religion, he hopes a candlelight vigil around the White House this month will remind official Washington of the horrors that one charismatic individual and a handful of believers can cause.