Gentle. Idealistic. Brilliant. Honest. Intense. This was Dennis Sweeney as a young student at Stanford University, as his friends remember him, before the hatred and violence of the 1960s exacted their toll.

Yesterday, the same man was arraigned in Manhattan Criminal Court for second-degree murder and held without bail. He reportedly confessed to police on videotape that he shot at least five bullets into Allard K. Lowenstein, his former mentor and idol, and then calmly sat down in Lowenstein's New York law office to await the consequences.

The story of Dennis Sweeney, once ashining son of the civil rights movement and of late an unemployed drifter with paranoid delusions, is a story of personal failure. But it is also a tale of the '60s -- a political story in a sense -- of burnt-out hopes and dreams gone sour.

Sweeney was of a generation that cared about injustice and showed it by marching in the violent South, by going to jail rather than to war, and, in some cases, by dying under police bullets on raging campuses. Mostly, these children have grown up to be lawyers, nurses, artists, mothers and fathers -- ordinary people with special memories.

Some dropped out to farm in rural communes. Some found solace in Eastern religions. Others, like Sweeney, never fully recovered, never truly reconciled ideals and reality.

Charles Hinkle, a friend from Stanford days, is a successful Portland lawyer, a former chairman of the OregonCivil Liberties Union. He says of Sweeney, "In a sense he was a paradigmfor a lot of young people who took part in the civil rights movement, then became radicalized.

"They became permanently alienated and were lost to us just as surely as those who were killed in Vietnam."

The adopted son of a Portland printer, Sweeney was recruited in 1964 by Lowenstein, a former Stanford dean, to join hundreds of young "freedom fighters" marching south to register blacks to vote. Lowenstein was an inspirational leader who attracted the best and the brightest, exciting intense loyalty and lasting friendship among thousands of young people.

Sweeney dropped out of Stanford after his third year at the age of 21 and spent almost two years in Mississippi. He lived in the town of McComb, the center of some of the mostviolent racial conflicts. He was injured slightly in July 1964 when bombs were thrown into the "Freedom House" where he and nine other civil rights workers were asleep.

It was in the South that Sweeney apparently met Mary King, a civil rights worker whom he married and later divorced. King is now deputy director of Action, parent agency of the Peace Corps, and is married to Dr. Peter Bourne, a former drug policy adviser to President Carter.

King was not available for comment yesterday. Bourne said in a telephone interview that Sweeney and King were married for "a matter of months" and have not seen or spoken to each other for years.

Ivanhoe Donaldson, an aide to Washington Mayor Marion Barry and a director of the Student Non-ViolentCoordinating Committee (SNCC), remembers Sweeney's arrival in Mississippi with a group organized by Lowenstein. "He was one of Al's proteges," Donaldson said, "He was very friendly, intelligent, a nice guy, a real middle-class kid."

David Harris, the former antiwar activist who married Joan Baez, lived with Sweeney for a year. "We were real close from '66 to '68," he said. "He was the leading civil rights figureon campus in the early '60s. He was very intense, very bright and painfully honest. He tended to internalize things."

But the murders, the bombings, the hatred Sweeney saw betweeen blacks and whites in the South radicalized himand disturbed him deeply enough to upset his emotional stability. He fought with Lowenstein, who was uncomfortable with the increasingly radical, black-power oriented direction of SNCC. Sweeney was one of the last whites to stay in the group.

"Lowenstein had led many young people into the civil rights movement," Hinkle said, "and Dennis thought he should have led them into radical politics.

While in Mississippi, Sweeney developed the delusion that a listening device had been planted in his teeth. A doctor from New York was doing free dental work for civil rights workers and Sweeney came to believe Lowenstein had ordered the device implanted, Hinkle said.

He went back to Stanford for two terms, but never graduated and, according to friends, lived in a Palo Alto antiwar commune, where he experimented with psychedelic drugs. From there, he drifted back to Portland, holding odd jobs as a carpenter, restaurant cook and dishwasher.

He lived for a time in Youngstown, Ohio, in Philadelphia and, at one point, was reportedly admitted for a week to a Portland hospital for psychiatric care. In 1973, according to a friend, several people close to Sweeney raised money to cover his treatment at a private mental hospital in the East. He stayed there about a week.