But the closing of 232 processing centers will be phased in over three years instead of the faster pace postal officials announced last fall.

“After input from our customers, we’ve modified our approach,” Postmaster General Patrick Donahoe said at a news conference. “But the sobering reality is that the First Class mail [volume] will not return.”

A U.S. Postal Service sign outside a post office in Fairfax County. (Andrew Harrer/Bloomberg)

The agency will consolidate — with full-scale closures in some cases and smaller operations in others — 140 mail processing centers in the next year, starting with 48 in July, officials said. The rest will occur in January and February, after the fall election and the busy fall mailing season.

Another 89 hubs will close or shrink operations in 2014. Postal officials said they will release a list of the first round of closures late Thursday. About 13,000 jobs will be lost from the closures, mostly through attrition, officials said.

The consolidations will affect delivery of First Class mail to some degree, officials said, with some letters arriving in three days instead of two. Local delivery would not change.

The modified approach to the mail hub plan follows an announcement last week that the Postal Service is backing away from plans to close 3,700 mostly rural post offices and instead will drastically slash hours at 13,000 post offices. The agency had originally planned to close 252 mail processing centers beginning this summer, but at the request of members of Congress put a moratorium on the closings until this week to give lawmakers time to pass a legislation.

But Congress is still stalled over a bill. The Postal Service does not need congressional approval to close plants and post offices, but with many lawmakers concerned about losing jobs in their districts, the agency agreed to hold off until last week.