WASHINGTON -- The U.S. Postal Service will stop delivering mail on Saturdays but continue to deliver packages six days a week under a plan aimed at saving about $2 billion, the financially struggling agency said.In an announcement scheduled for later Wednesday, the service is expected to say the Saturday mail cutback would begin in August. The move accentuates one of the agency's strong points -- package delivery has increased by 14% since 2010, officials said, while the delivery of letters and other mail has declined with the increasing use of email and other Internet use. Under the new plan, mail would still be delivered to post office boxes on Saturdays. Post offices now open on Saturdays would remain open on Saturdays. Over the past several years, the Postal Service has advocated shifting to a five-day delivery schedule for mail and packages -- and it repeatedly but unsuccessfully appealed to Congress to approve the move. Though an independent agency, the service gets no tax dollars for its day-to-day operations but is subject to congressional control. It was not immediately clear how the service could eliminate Saturday mail without congressional approval. But the agency clearly thinks it has a majority of the American public on its side regarding the change. Material prepared for the Wednesday press conference by Patrick R. Donahoe, postmaster general and CEO, said Postal Service market research and other research has indicated that nearly seven in 10 Americans support the switch to five-day delivery as a way for the Postal Service to reduce costs.