Dropping a first-class letter in the mail in the morning and expecting it will get to its destination by the next day would be a thing of the past under changes the U.S. Postal Service is explaining.

Dropping a first-class letter in the mail in the morning and expecting it will get to its destination by the next day would be a thing of the past under changes the U.S. Postal Service is detailing this hour.

But there will be no change in the Post Office's commitment to deliver a first-class letter anywhere in the continental U.S. within three days, spokesman Dave Williams just told reporters on a conference call.

Widely anticipated and laid out in broad terms back in September, the changes are part of a broad restructuring — which includes the anticipated closing of up to 250 or so processing facilities and the elimination of about 28,000 more jobs — as the Post Office looks for ways to stem the billions of dollars in red ink it is accumulating.

Williams said that among the other changes the Post Office wants to institute by next spring is to change "the geographic reach of our current 2-day standard" from about a 12-hour drive from a letter's point of origin to about 4-hours. In other words, the Post Office will guarantee delivery in two days or less within that 4-hour window. Anything beyond that, the guarantee is 3 days or less.

The Post Office estimates it would save $2.1 billion annually thanks to the changes, Williams added. it lost $5.1 billion in the past year, according to The Associated Press.

As for post offices in small towns and the likelihood that many will be closed in coming years, Williams said that is being studied. He also said the Post Office is not now seeking to eliminate Saturday delivery — but is still studying that as well.

We'll add more about today's additional details about the Post Office's plans later.

Before today's news conference, The Associated Press put together a video report on the expected changes. [Copyright 2011 National Public Radio]