As they approached the giant cross, each man, woman and child from the Roman Catholic Church of St. Benedict the Moor in Northeast Washington was handed a nail. Silently, each picked up a hammer and drove the nail into the wood, only inches from the outstretched arm of a parish priest.

For the 200 worshippers who joined in that solemn Good Friday service, the Christian concept of salavation and atonement became very personal.

"Our sins were the nails that were pounded into His [Christ's] hands and feet," the Rev. Thomas Frank, the assistant pastor at St. Benedict's, told the congregation. "Our intolerance of one another. . . our sins of indifference to our apathy."

Christians believe that Christ's death on the cross atones for their sins and that salvation is thus assured for those who believe in Him.

But the priest warned that action as well as belief is required of the faithful. "He [Christ] has promised eternal life to those who believe in Him," Frank said. "But we will not have eternal life in heaven unless we try to create a little heaven here on earth."

Frank encouraged the parishoners to be more diligent in putting Jesus' teachings of service and sacrifice into practice in their own lives. "The nails won't mean anything unless we accept a little bit more of what that cost in our daily lives," he said.

Yesterday's service at St. Benedict's, located at 320 21st St. NE, blended Negro spirituals and Gospel music with Catholic liturgy. Avon Gillespie, a member of the music faculty at the University of San Luis Obispo in California, chanted and sang the gospel account of the crucification.

Gillespie, in a long black cassock, assigfned the congregation its role in the service as the crowd in ancient Jerusalem that demanded Jesu's death.

"Become today that crowd, that ugly crowd," he said, "Speak with the knowledge that you, too, could have been among that crowd screaming for the blood of Jesus."

As the Gospel account told of Christ's trial. His abandonment by Peter and the other disciples, and His sentence of death, assistant pastor Frank, dressed in a stark white cassock and a deep-red stole moved to the back of the church.

There in the role of Christ, he shouldered the rough, eight-foot cross that two workmen had hammered together at the outset of the service. Staggering and sometimes falling under its weight, he moved slowley down the church aisle. At the front of the church, the top of the cross was placed on a trestle and Gillespie began the spiritual: "Those cruel people, hammerin', hammerin' . . . as the ritual of the nails began.