After four years behind bars, Pvt. Lindsey Scott, the 31-year-old black marine whose 1983 conviction of raping a white woman has been a cause celebre among civil rights groups, was set free yesterday while the Marine Corps decides whether to retry him.

Scott, who was stationed at the Quantico Marine Base when he was convicted of rape, sodomy, abduction and attempted murder, left the federal Disciplinary Barracks at Fort Leavenworth, Kan., at 11:30 a.m. Officially, he is on leave.

His conviction and sentence of 30 years at hard labor were overturned July 6 by the U.S. Court of Military Appeals, which ruled that lapses by his civilian attorney at the court-martial cast doubt on the verdict.

The court left open the question of whether Scott will face another court-martial. The Marine Corps said yesterday it will not decide whether to retry Scott for at least a month, and ordered him to report to the base at Quantico by Aug. 21.

Military authorities at Fort Leavenworth gave Scott a month's advance pay -- $652.20 before deductions -- and drove him to Kansas City International Airport for a flight home to Louisville, where he was met by about 25 relatives and friends.

{Many had yellow ribbons tied around their arms, and some held signs, saying variously, "Jesus Was Innocent and So Were You," "We Love You Lindsey" and "Welcome Home." Scott said, "It feels great to be home. I feel relieved," the Associated Press reported.}

The Rev. Patrick D. Delahanty, pastor of St. Charles/Holy Cross Church in Louisville where Scott's family worships, said Scott's parents had reserved a room at an undisclosed hotel in the city for Lindsey, his wife Lolita and their 3-year-old daughter Latavia, who was born after her father was incarcerated.

The hotel, Delahanty said, would afford Scott his first taste of privacy in years and a refuge from reporters who have been hounding the family since the court decision last week.

Lori Jackson, a Spotsylvania County, Va., civil rights activist who was part of Scott's defense team at his court-martial, said she was hopeful that the decision to free Scott presages dismissal of all charges against him. "If they thought Lindsey Scott was really guilty and had committed all these crimes," she said, "they'd release him into a controlled environment such as the military base or confine him to quarters."

But Delahanty, who raised more than $10,000 to pay for Scott's legal fees, said: "A new trial doesn't worry me. I don't think the evidence was there to begin with. Any jury who heard both sides of this . . . is going to conclude that Lindsey Scott was in a Zayre store and wasn't on some military base raping anybody." Scott has said he was shopping at a Zayre in Woodbridge at the time of the attack.

Lt. Gen. Frank E. Petersen Jr., commanding general of Quantico, made the decision to free Scott rather than return him immediately to Quantico for pretrial detention or confinement to the barracks there. Petersen has the responsibility to decide whether to retry Scott.

When Scott returns to Quantico, he will be assigned to the Security Battalion, his old unit where he worked as a military policeman before he became a suspect. His duties will be determined at that time, according to a marine spokesman.

Scott became a suspect in the case almost immediately after the 23-year-old wife of a military policeman who worked with Scott was found bleeding and dazed on the Quantico base the night of April 20, 1983.

She told investigators she had been lured from her apartment hours earlier by a telephone call from a man who said her husband had been in an accident and offered to take her to the hospital.

Instead of driving to the hospital, the man drove her to a remote spot, raped her, choked her, stabbed her in the neck and slashed her throat. The military investigation immediately focused on Scott, leading civil rights groups to complain that authorities were eager to charge any black man who fit the woman's imprecise description of her assailant.

The Marine Corps has denied its investigation was racially tinged.