 The primary objectives of this study are to compare the efficacy, safety, and tolerability of tenofovir disoproxil fumarate TDF versus adefovir dipivoxil ADV for the treatment of HBeAg-positive chronic hepatitis B. Participants will receive TDF or ADV for 48 weeks double-blind. After 48 weeks, eligible participants switched to open-label TDF for up to 480 weeks. 