A family knelt in prayer yesterday at St. Mary's Catholic Church in Old Town Alexandria with 60 of their friends as the priest spoke of the "mystery of life."

For Jean and Donald Sawtelle, however, it was what they called the "miracle of life" that sustained them as they prayed for the recovery of their son, Mark shot in a holdup attempt that has shocked the city's Old Town residents.

"The doctors haven't called it a miracle yet, but that's what it was," said Jean Sawtelle, a Fairfield, N.J., housewife who flew to Washington shortly after hearing about the shooting.

Mark Chase Sawtelle, 28, who handles inquiries for Time-Life Books in Alexandria, was shot twice in the chest in broad daylight as he was getting into his station wagon at the intersection of Wolfe and South Columbus streets in the center of Alexandria. Two men were arrested minutes after the incident and charged with assault and robbery.

"He still can't grasp it happened to him," said Sawtelle's wife, Elaine, a writer for a trade group in Washington. "He said to me 'I can't believe he shot me,'" she recalled.

One .38-caliber bullet remains in Sawtelle's right shoulder. Another passed through his stomach and lodged in the door of one of the area's refurbished town houses, officials said. He was listed in "fair" condition yesterday at Alexandria Hospital.

Sawtelle may owe his life to his surroundings in the city that prides itself on its small town virtues.

"I have no doubt that the speed with which witnesses called us saved his life," said Alexandria Detective Louis Pugh. "He was shot at point-blank range in the chest and stomach. In a case like that, we're talking about a matter of minutes between life and death," he added.

The shooting was one of an increasing number of crimes that has sent Alexandria's crime rate soaring, police said. In 1979, crimes in the Northern Virginia city jumped an alarming 21 percent higher than in 1978, according to police statistician Sgt. John Steadman. Although most of the crimes do not involve violence, Steadman said they may be changing.

"I've been anticipating something like this," he said of the Sawtelle shooting. "There's been an enormous increase in the number of guns we've been recovering lately."

What troubles many Old Town residents about the shooting was its location and the time of day it occurred.

Sawtelle, was shot at 5:47 p.m. during the evening rush hour within sight of his small apartment at 321 S Washington St. The shooting was within sight of his Time-Life office at the corner of Duke and Washington streets a major intersection.

Within moments of the shooting, the Alexandria police switchboard lit up with calls from witnesses. One of the first came from Robert Rose, an Eastern Airlines flight attendant who lives at 718 Wolfe St. "We've had so many burglaries from cars around here that at first I thought this was just another one," he said.

Rose quickly realized that this was more serious, as did Gloria Howell, a passing motorist who saw the robbery begin. She drove around a block to a service station to summon help, and then returned to the scene. "Suddenly this man opened the door to my car, said, 'Help me . . . I've been shot,'" she recalled.

The man, bleeding profusely, climbed into her car and she headed for a hospital. To her surprise, Howell pulled into traffic behind a car that she believed contained Sawtelle's assailants. "I wrote the license tag on a check," she said.

Officers arrested two men two blocks from the scene and charged them with assault and robbery. They were identified by police as David Emerson McNair, 20, and Alfred E. Rice, 33, both of Washington. They were being held in Alexandria jail yesterday pending a court hearing Monday.