Of the more than 8,000 physicians licensed to work in the nation's capital, only 453 of them are primary-care doctors who spend more than 20 hours a week seeing patients, according to a report released Wednesday by the D.C. Board of Medicine. The number of actively practicing primary-care doctors comes from a survey conducted when doctors renewed their licenses last year. It puts a number on a complaint that patients and health-care providers have long had: It's hard to find a doctor in Washington.