(Justin Sullivan/Getty Images)

Senators voted 74 to 22 to proceed to debate on the bill, with less than a month left until postal officials say they plan to begin closing hundreds of post offices and processing facilities. Congress requested that USPS wait to close facilities until mid-May so that lawmakers could pass legislation to help USPS save about $22.5 billion by 2016 by curtailing delivery services, closing facilities and offering buyouts to hundreds of thousands of workers.

The bill set for debate is co-sponsored by Sens. Joseph I. Lieberman (I-Conn.), Susan Collins (R-Maine), Tom Carper (D-Del.) and Scott Brown (R-Mass.) and would delay the Postal Service’s move to a five-day delivery schedule for at least two more years while requiring the agency to downsize, rather than close, most of the processing facilities it wants to close.

It also would permit USPS to deliver mail to curbside, sidewalk or centralized mailboxes instead of to front doors or mail slots, allow the service to ship beer, wine and spirits and to explore other sources of revenue. The Postal Service would have to continue overnight delivery of first-class mail, but limit it in some cases to shorter geographic distances.

Six-day delivery service would be scrapped only after the Government Accountability Office conducts a thorough study and determines that the Postal Service has no other way of cutting a considerable amount of operation costs.

Addressing one of the most controversial aspects of postal reform, the bill would require USPS to work with communities before shuttering post offices to determine what type of postal retail service best meets local needs — perhaps a traditional post office, or placing postal workers at a kiosk within a large nearby supermarket. The bill also permits affected areas to appeal a decision to close a post office to the Postal Regulatory Commission.

Lieberman called the bill “a reasonable and balanced approach to the Postal Service’s deep financial problems,” adding later that “We believe this approach offers the best hope for stabilizing the Postal Service and putting it on solid footing long-term, without dramatic and perhaps self-defeating cutbacks in service.”

But a GAO report released last week said delays in ending Saturday mail deliveries “could make it difficult” for USPS to save $22.5 billion by 2016 as planned. But the Senate proposal also would provide money for USPS to offer buyouts to as many as 100,000 eligible workers — a plan that would help USPS meet cost-cutting goals, GAO said.

As the debate begins, a business group representing some of the Postal Service’s largest customers warned Tuesday that lawmakers should avoid raising first-class postage rates beyond the current 45 cents. Any dramatic rate hike “would have a dramatic impact on business mailers, and would ultimately hurt the U.S. Postal Service,” said Jim Morrell, a spokesman for the Coalition for a 21st Century Postal Service, which represents retailers, magazine publishers and other bulk mailers.

A competing House Republican proposal not yet introduced for a full vote includes plans for a panel similar to the Defense Base Closure and Realignment Commission to address the issue of closing post offices and processing facilities. The bill’s GOP sponsors think the panel would help remove political and labor concerns from the closing process.

Senate Democratic aides expect postal reform to dominate the week’s deliberations and that the Senate will move next to a vote on reauthorizing the Violence Against Women Act.

Follow Ed O’Keefe on Twitter: @edatpost