The Postal Service took the first formal step toward cutting mail delivery to five days a week.

The postal governing board agreed to ask the independent Postal Regulatory Commission for an opinion on dropping Saturday delivery. That request goes to the commission next week.

Under the proposal, mail delivery to homes and businesses and mail collection from blue mailboxes would be limited to Monday through Friday.

However, post offices that are now open on Saturdays would remain open, and Express Mail delivery service would still be available seven days a week.

Beyond getting the regulatory commission’s opinion, the Postal Service needs Congress to approve the change.

The Postal Service says the delivery change would save more than $3 billion annually. It is a major part of a decade-long plan to eliminate losses and restore the agency to stability in the face of shrinking business.

As Americans turned more and more from paper to electronic communications, the number of items handled by the post office fell from 213 billion in 2006 to 177 billion last year. Volume is expected to shrink to 150 billion by 2020.

The post office lost $3.8 billion last year and is facing projected losses of as much as $7 billion this year. Other proposals for cutting losses include changes in the financing of retiree health care and closing some mail handling centers and post offices.

Postal Vice President Sam Pulcrano said the agency has set up a Web site where people can learn about the proposal: http://www.usps.com/communications/five-daydelivery/.