'IT'S the most glorious thing that could happen in my life - to wake up every day and see the changes here," says Rita Webb Smith.She is talking about this block on West 143rd Street in Harlem which in the late 1970s was a thriving drug market. Her son David was shot in the chin by a drug dealer right in front of this brown-brick apartment building where she was born, raised her seven children, and where she still lives. Next door is the "survival clinic" that she now runs with volunteers to help her neighbors get needed city services. Mrs. Smith recalls that as the violence closed in, she faced a clear choice: accepting it or doing something about it. She convinced her neighbors to work together with area police who were largely white and had been treated with hostility by many residents since the 1960s riots. "Without community leaders like Rita breaking down the barriers ... it couldn't have been done," says retired police lieutenant Peter Pranzo, then a member of the city's narcotics task force. Area drug dealers soon got the message. Mrs. Smith, who went on to college and got a master's degree in social work from Fordham University, then began to work with former New York Mayor Edward Koch to rebuild some of the area's rundown housing with the last federal Section 8 money available. As she takes reporters and church leaders on a neighborhood walking tour, she is quick to point to areas that still need attention: "That building over there has no heat or hot water and nobody's doing anything about it." Indeed, Mrs. Smith, who is the subject and co-author of a recent book called "The Woman Who Took Back the Streets," says she will not be satisfied until citizens everywhere take back their streets. "There isn't anybody in this country who isn't touched by the drug problem," she says. "W e all have to become involved."