TWO MONTHS before the great civil rights march of 1963, Medgar Evers, field secretary for the NAACP working in Mississippi, was shot to death in his own driveway. Though it was not unusual for rights workers to be assaulted and even killed in the Deep South in those days, this murder was especially well publicized because of the victim's national stature. Mr. Evers, a nonviolent man who had successfully organized some early demonstrations and protests, was well known and greatly admired, and his death was a profound shock to the civil rights community.

A white supremacist named Byron De La Beckwith, whose fingerprint was found on the murder weapon, was arrested and charged with the crime. Few whites in those days were convicted of killing blacks in the South, and it is an indication of how widespread racial injustice was that the very fact that he was brought to trial was considered progress. In fact, he was tried twice in 1964, but neither jury was able to agree on a verdict. Again, those disappointed in the outcome were consoled by the fact that neither jury acquitted the defendant outright, which is what many feared and expected would happen. It is that failure either to convict or acquit that has enabled Mississippi prosecutors to move now -- 26 years later -- finally to resolve the case.

Yesterday, Byron De La Beckwith was indicted once again for the murder of Medgar Evers. He was arrested at his home in Tennessee and will be returned to Mississippi for trial. District Attorney Ed Peters says he has new evidence, not introduced at the 1964 trials, that convinces him he can win a conviction this time.

Twenty-six years is a long time, and Mississippi has changed. While no one knows at this time whether the accused man is guilty, there are at least three reasons to assume the prosecutor will have an easier time making his case now than in 1964.

The political climate has changed dramatically, and officeholders of both parties know they must appeal to black voters. One of the state's five members of Congress is black, as is a Supreme Court justice. Whites do not control the entire mechanism of government, and blacks can no longer be intimidated or ignored.

Political change has reached the courthouse. There are few judges who are openly hostile to blacks, prosecutors who believe in separate and unequal standards of justice, or witnesses who are, for reasons of race, too terrified to testify in public.

Finally, the U.S. Supreme Court recently barred the practice of excluding blacks from juries in criminal cases. All the jurors in both of Mr. De La Beckwith's earlier trials were white. There is every reason to hope that this time the question of who killed Medgar Evers will be fairly and finally resolved.