Spurred by the prosecution of six black inmates accused of slaying a white prison guard and two white inmates during riots at the George state penitentiary near Reidsville last summer, a group has set off an 80-mile march from Savannah to the prison.

The trek was marred by tragedy, however. Today, during a rest stop near Pembroke, Ga., a 19-year-old protest marcher drowned while swimming in the Canoochee River to cool off. The victim identified as Arthur Ashley Norwood Jr. of Savannah, "hit the current, which is pretty swift at this time of year, and just went down and drowned," authorities said.

The marchers, who call themselves the Coalition for a March on Reidsville, claim to be the vanguard of a new nationwide prison reform movement.

Led by Hosea Williams, president of the Southern Christian Leadership Conference in Atlanta and a member of the Georgia House of Representatives, and comedian activist Dick Gregory, the marchers left Savannah Monday, demanding that the state close its maximum-security institution because of alleged inhumane conditions there. State troopers and sheriff's deputies escorted the marchers.

They also charge that the black inmates, "the Reidsville Six" have been singled out of the 200 prisoners who rioted because they were outspoken critics of the prison administration. Three black inmates, two white prisoners and a white guard were killed during the disturbances, which lasted from March through August of 1978.

One of the black inmates has received a life sentence for taking part in the killings, and naother is standing trial on the charges this week. Three white inmates await trial for the attacks against the blacks.

"The white guards are actually sentencing the [black] prisoners to death by issuing the whites contraband weapons," Williams said as he and a column about 30 strong trudged along U.S. 80 beneath the burning mid-day Georgia sun. "This is a microcosm of the prison system in the country," he added.

They are also protesting the death penalty, which they say is most frequently inflicted on blacks and poor whites. "The way the death penalty is carried out it does no good,"; Williams said. "States like Georgia, Mississippi and Alabama have had it for years and they've always had a higher capital crime rate."

The march, which will end with a rally at the prison gates Saturday, coincides with the visit in the South of the former Trinidad-Tobago chief justice, Sir H. Arthur McShine, who has sat in on brief portions of the trial going on in Tattnall County courthouse this week and met with three of the other black defendants.

McShine arrived in Savannah Monday and will inspect state prisons in Alabama, Louisiana and Mississippi to investigate charges made in a petition delivered to the United Nations last year. He is part of a group of eight international jurists who propose to find out if the petition warrants their support.

The petition charges that imprisonment for political offenses is far from unknown in this country and that prison conditions are generally inhumane. It was submitted by several civil rights and civil liberties groups that subsequently invited McShine and the other jurists to the United States,.

McShine, who said today that "it's a little too early," to disclose any of the findings of his prison tour, also met with Georgia Department of Offender Rehablitation Commissioner David Evans in a visit he described as "very pleasant."

McShine will meet with State Department and Department of Justice officials after his investigation; he and the other jurists will submit their findings to the National Conference of Black Lawyers, which then must decide whether or not to submit the report to the U.N. Commission on Human Rights, which meets in Geneva later this month.

Although the marchers say they expect no trouble during their four-day trek, state prison officials have forbidden them from entering the Reidsville compound, where fenced guard lines have been erected.

Evans has declared that the prison will not be closed. Department of Offender Rehabilitation assistant Sara Passmore said the Reidsville prison population, which is 65 percent black and 35 percent white, has been reduced under pressure of federal court orders to 2,193, but declined to reveal how many prisoners the 42-year-old facility was meant to hold.

SCLC executive assistant Keith Wimbush reported, "The changes at best are cosmetic and geared toward diffusing our public support."

He and other protectors called for a new corrections system, one that included more jobs and work-release programs for "people who only commit crimes against property out of survival instincts."