The U.S. Postal Service on Monday unveiled proposed changes that would slow the delivery of the nation’s mail as the cash-strapped agency seeks to save billions of dollars by closing hundreds of mail processing facilities and cutting tens of thousands of jobs.

If enacted, the changes would take affect in March at the earliest and upend a standard practice since the 1970s that now delivers about 96 percent of first-class mail overnight.

With first-class mail volume plummeting about seven percent annually, “We’ve got more capacity in our [delivery] network than we can afford,” Postal Service Vice President David Williams said Monday.

First-class mail deliveries peaked at 104 billion pieces in 2001, according to Williams, but fell to 73.5 billion pieces delivered last year. USPS is likely to process just 39 billion pieces of first-class mail annually by 2020 — a 46 percent drop from 2001.

“We’ve got to set our network up so that when volume continues to drop, our network is nimble and flexible enough to respond to those volume losses,” Williams said.

USPS wants to shutter about half of its remaining 461 mail processing facilities; 26 have closed since September, Williams said. The changes should save USPS about $2.1 billion annually and trim at least 28,000 jobs, part of a broader plan to cut $20 billion in costs and as many as 120,000 positions by 2015.

Closing the processing facilities — which could leave some western states with just one central location to sort mail — would lengthen the distance a piece of mail travels between its initial drop-off point and its final destination, likely meaning slower delivery of letters, DVD rentals, mail-order prescriptions and magazines.

Under the proposed changes, some bulk mailers of catalogs, magazines and bill payments would be eligible for overnight deliveries if they meet specific drop-off schedules and packaging requirements. But everyday Americans hoping to mail a birthday card or invitation overnight to nearby family and friends would have to wait at least two days for that mail to arrive, officials said Monday.

In an e-mail Monday The Economist magazine alerted readers that it is monitoring the Postal Service’s changes and looking at other delivery options, including local newspaper delivery services, to ensure the timely distribution of its weekly publication. The magazine encouraged readers to access its Web and mobile sites for the latest editions if print copies fail to arrive on time.

The USPS plans, submitted Monday to the Postal Regulatory Commission and published in the Federal Register, are open to public comment before final implementation. Postal regulators may issue a nonbinding opinion on the proposals at a later date.

On Capitol Hill, Sen. Susan Collins (R-Maine) said the Postal Service’s proposed changes “could well accelerate its death spiral” and called on her colleagues to quickly pass postal reform bills pending in the House and the Senate.

Follow Ed O’Keefe on Twitter: @edatpost

Further reading:

Postal Service mulls eMailbox option

Unions blast GOP plan to extend federal pay freeze

For more, visit PostPolitics and The Fed Page.