Breathless from a set of 50-yard drills, the swimmer shouts, "How'd I do, Coach?" "Nice job!" comes the answer, "Your best time was 36.5 seconds." Not exactly an Olympic time, but then, this swimmer is a 72-year-old grandmother, Rita Shephard of College Park. Mrs. Shephard, who started swimming competitively at the age of 65, is representative of the recent surge of adult interest in swimming. Encouraged by her daughter, who was in a masters swim program, Mrs. Shephard began practicing back in Ohio. "When I started," she recalls, "I swam with a high-school team so I could learn the rules. The kids were really nice about helping. After only 11 weeks of practice I went to the masters nationals in California and took a second and three firsts!" Since she moved to Washington five years ago, Mrs. Shephard has been representing the D.C. masters team at national meets, the oldest woman on the team. But at 81, Steve Craigi is still swimming for the men, and many others across the country are swimming competitively into their 80s. John Flanagan, coach at the Fun and Fitness Center in Arlington, says, "Washington has always had more people interested in athletics than almost anywhere else. People have been swimming like crazy here for at least ten years." Greg Gordon, pool manager at Wilson High School, points out: "When it's too cold out to jog, eveyone comes inside to swim." Along with the surge in natatory (fancy word for swimming) interest in the area has come a burgeoning of indoor pools. Just six years ago Prince George's County had no indoor pool facilities at all, and now there are two big public complexes. As recently as 1977 Fairfax County had no public facilities, and now it has three, with a fourth opening shortly. Montgomery County now has a major indoor facility in each of its most populous regions except Bethesda-Chevy Chase, with one or two more under discussion. For lunchtime athletes in the District, indoor swimming possiblities are very limited, but before or after school and on weekends a city-wide network of high-school pools is available. No matter where you live in the area, you probably have an indoor pool within easy reach; just pick it out of the list below and plunge in. If you already belong to a pool and don't see it listed here, it's because those with long waiting lists were excluded. University pools do not appear because they are, for the most part, closed to the public. All these pools are available, athough some are more expensive or more crowded than others. The older pools are measured in yards, the newer ones in meters. A 25-meter (81-foot) pool is six feet longer than a 25-yard (75- foot) pool. Most pools in the area are 25 yards, with exceptions noted below. Those that offer something unique in their geographical areas or provide special classes or services are noted. Fees and available pool times are always open to change, so call before you go. Last one in is a rotten egg!