He is Super Charlie, the Great White Viet Cong. A figure of myth, terror and contempt who glides through the jungle on sandals crafted from jeep tires. He lurks in the darkness outside infantry encampments and tells the Americans, through a battery-powered electric megaphone, that their cause is doomed as well as wrong. They should put down their weapons and refuse to fight.

Then he slips away, a wraith in a wilderness. Often he is shot at. Sometimes he is pursued. Once he is trapped in a tunnel with no place to hide. But he escapes somehow, never to be caught.

He trudges tirelessly along the supply trails of the National Liberation Front carrying supplies on his wide shoulders. He speaks flawless Vietnamese, then drops with equal fluency into dialects of the hill people who call him friend -- who have even permitted his involvement with one of their women.

The Marxist Vietnamese accept him completely, commission him in their army, and name him Huyen Din Dao, son of revolutionaries. He is not quite a straight arrow. Sometimes he steals eggs for his fellow Americans. Once, when it squawked as he was raiding a nest, he even strangled one of the camp chickens, and shared this also, though not generously.

This is the surprising picture of turncoat marine Robert Garwood now emerging from testimony against him at a preliminary hearing on charges that Garwood deserted to the communists in Vietnam and collaborated with them at the height of the U.S. military involvement in the war there.

Turncoats are supposed to be weaklings, fighting men who have cracked under pressure, screwballs who never did have their heads on straight. They seldom evoke grander emotions than pity.

Garwood started out in the mold; 10th-grade dropout at Adams, Ind., son of a small-town printer, to all appearances a callow and umpromising youth when he left the Marines for the Viet Cong near Da Nang in 1965.

Yet some aware of his history might not find him pitiable now. He has gained at least 50 pounds since coming home and is a tall, well-built, solid but trim young man with an open face. He is losing some of his hair and there are a few premature worry wrinkles around his eyes, but he does not look especially older than his 33 years.

As he sits with his lawyers at the defense table in the military courtroom here he seems disciplined and distant, as if his concentration were focused on something in the middle distance. Like the Marine lawyer who sits closest to him, Capt. Joseph Composto of New York, he wears a wooly-pully, a Marine green sweater. He does not look more like a defendant than Composto or the other marines in the room.

He is about 6 feet tall; perhaps 6-1. An early account, published when he was still in Vietnam, put his height at 6-3. The former prisoners of war who are his accusers (and who have told us most of what we know about his war record) seem to find themselves torn between their anger, their need to justify their own accommodations to their captors, and some unacknowledged sense of awe.

They see Bobby Garwood (no one calls him Robert, and few Bob) as the ultimate kind of evil that they have known too well. But they often describe him also as two or three inches bigger than life.

"To me he was like a white Vietnamese," testified Gustav Mehrer, an Army man who listed his occupation as disabled veteran. "The way he spoke, the way he laughed when he was overjoyed, the way he squatted, the way he walked . . . . He seemed like he was one of them."

Most recollections are less specific. Garwood comes and goes in the memories of these POWs, sitting with Vietnamese in judgment on them, guarding them, exhorting them to join the revolution, boasting of his own exploits.

Since none of the prisoners were around to see him use his bullhorn on American fire bases, they can testify only to hearing about it. He is said to have told a Vietnamese guard -- presumably in English, because he was overheard and understood -- that he had fired on American troops, in self-defense.

All five of the former POWs who testified against Garwood in the preliminary hearing last week have acknowledged that they have collaborated with their captors in ways that represent a departure from the code of conduct that binds U.S. POWs. They wrote letters and other appeals for an end to the war in which they parroted standard Vietnamese rhetoric. But they also did other things -- whatever their captors were determined to have them do, as Sgt. Willie Watkins put it under cross-examination.

Acknowledging that he had made anti-American statements, Chief Warrant Officer Francis G. Anton of Fort Dix said: "The first time was with a .45 [pistol] at my head. After that there was the fear. I don't think carrying a rifle [as Garwood is accused of doing] can be equated with that." c

Garwood went whole hog, in other words. His own accounts are baffling. "I did not betray the United States but I betrayed the involvement of the United States in Vietnam," he told broadcast journalists just before leaving Hanoi eight months ago. "I don't know if you consider me as a peace-fighter or not, but I was not in callaboration with the Vietnamese. I was in collaboration with the people of the United States against the involvement of the United States government in Vietnam." He is now almost completely muzzled by his lawyer and has offered no explication.

Most Americans had never heard of Garwood before last March, when he returned to the United States after slipping a note to a foreigner in North Vietnam saying he wanted out. But he has been an important figure for more than a decade in specialized branch of military affairs, what might be called POW studies.

He was identified years ago as a turncoat with a bullhorn and gun and has been named in many magazine articles.

He plays a central role in a book about POWs, "Survivors" by Zalin Grant, that was published in 1975.

This book has been scored as inaccurate by Garwood's lawyer, Dermont Foley; and by the POWs who have mentioned it as they've testified. But much of the testimony has sounded as if it came directly from "Survivors."

When Anton was asked about this after his own testimony, he recalled remarking on the witness stand that most of the assertions in the book contained a kernel of truth.

Much of the testimony is also vague, and apparently destined to get more so. Foley and the two Marine lawyers who are assisting him spent much of last week arguing for access to unedited tape recordings of interviews with intelligence officers that the witnesses made when they returned to the United States.

This issue remains unresolved. One result of it is that the first four witnesses left the stand without being cross-examined.

Foley, who seems competent, low-keyed and shrewd, now has five independent, sometimes conflicting accounts of events that happened more than 10 years ago with which to manufacture mischief for the prosecution.

He already has done that with Sgt. Willie Watkins, the fifth witness and the first to be cross-examined. Under Foley's prodding, Watkins qualified or backed away from much of his testimony.

So far, most of Garwood's 13 1/2 years with the Vietnamese communists are unexplained. Testimony at the inquiry had covered only prison camps in South Vietnam in 1968 to 1969. He says he was wounded and captured by the Viet Cong and kept as a prisoner thereafter. The Marines say he went over voluntarily and the Vietnamese government says that he was not sent home with the last American prisoners of war, in 1974, because he was a free man, in Vietnam voluntarily.

Even without the prospect of a court-martial, his life would seem no bed of roses. Family members and other close to him say he has a lung ailment, a tropical fever and heart trouble, among other things. Foley contends that his client is also emotionally distressed, and that help has been unavailable because any psychoterapist called in might be forced to testify in millitary court. He has kept Garwood for exhaustive medical tests for similar reasons.

Garwood is a free man working as a mail clerk at Camp Lejeune. For several months he has lived with friends in nearby Jacksonville, N.C.

One of the friends, Dale Long, was killed in September when a 68-year-old retired man since convicted of driving while drinking ran down Long's motorcycle. Garwood still lives with Long's widow, Donna Long and her two sons, aged 9 and 14. Garwood's sister, Linda 20, also lives with the family. Mrs. Long is a bookkeeper for a motorcycle dealership. She inherited one-third ownership of the dealership from her husband, a Marine Reserve flier.

As did her deceased husband, Mrs. Long wears a bracelet memorializing an American serviceman missing in action in Vietnam.

She says her husband brought Garwood home to live after windows were broken at his barracks.

Garwood has never been promoted, like other prisoners of war. At stake in the court proceeding are about $150,000 in back pay that accumulated while he was in Vietnam.