WASHINGTON – Check your mailbox: If the U.S. Postal Service has its way, today could be one of the last Saturdays you receive mail.

The mail agency is determined to end six-day mail deliveries and close unprofitable post offices after estimating $6 billion in losses for the fiscal year that ended Thursday.

The Postal Service earned about $68 billion in revenue in fiscal 2010, on par with last year, according to preliminary figures announced Friday.

It lost money for the third consecutive year as customers made wider use of the Internet to pay bills, purchase goods and send personal messages. Letter carriers delivered about 170 billion pieces of mail in fiscal 2010, about 7 billion fewer than last year, Postmaster General John Potter said.

The announcement capped a difficult week for the Postal Service: Regulators denied a request to raise stamp prices in January by 2 cents, and Congress decided not to reduce the $5.5 billion payment the agency is required to make by law to prefund health benefits for retiring postal workers.

Final revenue and volume figures will be released later this fall, Potter said.

“We have not changed in terms of what’s next,” he said Friday in a meeting with reporters. “We need to try and grow revenue. We’ll continue to use any tool that we can.”

Potter wants the agency to be able to set delivery schedules and routes without interference from Congress. He’d also like to sell products and services besides boxes and stamps — perhaps insurance, banking and cell phone services.

But Sen. Susan Collins of Maine and other Republican lawmakers say Potter should find deeper spending cuts before lawmakers approve new revenue streams.

“The problem is that every three years, it seems the Postal Service has been in financial crisis,” Collins said, referring to similar periods in 2003 and 2006. She plans to introduce new postal reform legislation and is urging Potter to review spending cuts proposed in a series of watchdog reports released last week, including consolidation of regional offices.

The Postal Service is in the midst of a 10-year plan to trim $120 billion in costs, Potter said. It now employs about 584,000 full-time workers, a drop of about 100,000 career positions in three years, he said.

“It’s been a tough few months for the Postal Service in terms of its management and relations with Congress,” Ruth Goldway, chairman of the Postal Regulatory Commission, said in an interview this week.

“But on the other hand, it appears from what we can see on the street that things are improving. They don’t have all their problems solved, but volume is going back up, and they have their costs under control.”

Amid declining revenue and congressional gridlock, Potter, the longest-serving postmaster in U.S. history, didn’t rule out leaving the Postal Service as some aides and other observers have suggested.

“I’m going back to my office,” he said Friday when twice asked if he plans to retire.