Washington - The financially struggling U.S. Postal Service announced Wednesday that it plans to stop delivering mail on Saturdays starting Aug. 1 - but will continue delivering packages.

Unless forbidden to do so by Congress, which has moved in the past to prohibit five-day-a-week delivery, the agency for the first time will delivery mail only Monday through Friday. The move will save about $2 billion a year for the Postal Service, which has suffered tens of billions of dollars in losses in recent years with the advent of the Internet and e-commerce, officials said.

"The American public understands the financial challenges of the Postal Service and supports these steps as a responsible and reasonable approach to improving our financial situation," Postmaster General Patrick Donahoe said at a news conference. "The Postal Service has a responsibility to take the steps necessary to return to long-term financial stability and ensure the continued affordability of the U.S. Mail."

The postal service plans to continue Saturday delivery of packages, which remains a profitable and growing part of the delivery business. Post offices would remain open on Saturdays so that customers can drop off mail or packages, buy postage stamps or access their post office boxes, officials said. But hours likely would be reduced at thousands of smaller locations, they said.

The Postal Service said it suffered a $15.9 billion net loss for fiscal 2012, which ended Sept. 30. That's three times the loss recorded a year earlier.

The Postal Service has pushed to cancel Saturday mail delivery for years. It announced the decision Wednesday without congressional approval, even though lawmakers have argued that their consent is necessary to make the operational change. Postal officials are expected to argue that they do not need congressional action to halt Saturday delivery.

In the past, Congress has included a ban on five-day-a-week mail delivery in its appropriations bill. But the Postal Service is currently operating under a temporary spending measure, rather than an appropriations bill, and the agency is asking Congress not to reimpose the restriction when the spending measure expires March 27.

A majority of Americans support ending Saturday mail, according to national polls conducted in recent years, and President Barack Obama has proposed halting deliveries as part of his budget-cutting proposals. Though the Postal Service is a quasi-governmental, self-funding entity, its worker compensation and retirement plans are tied to the federal budget.

Lawmakers have tried unsuccessfully for years to enact a significant overhaul of the Postal Service, hoping to reshape the agency as a leaner organization that delivers mail less frequently and operates fewer post offices across the country.

The Senate last year passed a bipartisan measure that would have permitted an end to Saturday mail delivery only after USPS conducted two years of feasibility studies. But postal officials - and some GOP lawmakers - opposed that plan, arguing that reams of professional studies and a declining balance sheet already proved that the change was needed.

A Republican-backed postal reform bill cleared a key committee last year but was never considered by the full House. The GOP bill would have permitted ending Saturday mail deliveries within a year.

Opposition to significant changes rests mostly with lawmakers from far-flung rural communities, who fear that a change in schedules could jeopardize low-cost delivery of medicines and medical supplies to elderly customers. The publishing industry also has complained that any changes would force quicker magazine publication deadlines and require some publishers to seek private delivery options instead, likely raising newsstand prices.

In a statement Wednesday, Jeannette Dwyer, president of the National Rural Letter Carriers' Association, said the USPS announcement amounts to "yet another death knell for the quality service provided by the U.S. Postal Service."

"For decades, the Postal Service has upheld a personal and professional standard of service, delivering to every household nationwide six days a week," Dwyer said. "To erode this service will undermine the Postal Service's core mission and is completely unacceptable."