The Atkins Tennis Center is celebrating its third year of operation by offering an expanded variety of leagues, adult and junior lessons, tournaments and special events. The center also sells permanent court time for an 18-week session. Courts may be reserved on a day-to-day basis depending on availability. The indoor season will open Sunday with a series of free events for all levels of ability: * Sunday, 4:30-6 p.m., Drill 'Til You Drop * Tuesday, 7-8:30 p.m., Beginners clinic * Wednesday, 7-8:30 p.m., Intermediate clinic and workout * Sept. 9, 7-8:30 p.m., Advanced workout The center, which serves the UI and residents of Champaign-Urbana, was recently voted the "most outstanding facility in the United States" by the U.S. Tennis Association. More information is available by calling 244-856.