WASHINGTON — There are, in many ways, two U.S. Postal Services.

There is the one that people love to hate, especially after a hike in rates such as last week's two-penny jump. This is the Postal Service that made Mark Tornga, 24, hold his head in disbelief as he walked out of a downtown post office at 4:30 one afternoon last week. "Fifty-two minutes I spent in line — 52 minutes!" he fulminated after sending a certified letter for his employer, a public relations firm.

Then there is the Postal Service that has made huge strides in on-time delivery, runs one of the most impressively automated operations in the world and, for now, is bringing in a huge profit. This is the Postal Service that customers such as Tornga don't see, and take for granted — the one that moves 580 million pieces of mail a day with remarkable speed and accuracy to every address in the nation, six days a week.

The first Postal Service is the one that executives are trying to fix, the one with the bad rap, the one that delivers mail late, the one that drives people crazy with its long lines and sold-out 2-cent stamps.

The other Postal Service is the one they are trying to save.

"Am I optimistic or pessimistic? I'd have to say I'm anxious," said John Nolan, who retired last year as deputy postmaster general and now works as a consultant.

The structural problems facing the Postal Service are monumental. Despite a tiny uptick last year, first-class mail volume is slowly but steadily eroding as people pay more bills online, send Evites instead of printed invitations and type e-mails rather than write letters. The agency also is facing massive and escalating personnel costs, especially for healthcare, even as it has embraced automation and reduced staffing needs.

Without making some hard decisions — and revisions — in the near term, Nolan and others say, the Postal Service "is on a crash course with cataclysmic change."

What kind of change and when is unclear. Privatization? Shuttered post offices? Dramatically more expensive mail? Less frequent delivery? It could be any of those things — or none of them.

And this is when people start thinking about the third Postal Service — the one that delivers possibility six days a week — a letter from an old friend, a tax refund or an acceptance from the admissions office. This is the post office that brings us the letter carriers we admire, who avoid dogs and leave footprints in pristine snow. It gives the tiniest towns their own proud postmarks. It's the post office that found you even when the address under your name was so incredibly incorrect it was laughable.

This is the Postal Service that no one wants to lose.

One way postal officials have been keeping customers happy is by keeping them out of the post office.

There are the post office's retail partners, grocers in particular, that sell books of stamps, which has become one of the most common ways people buy stamps.

There's the almost-four-year-old Click-N-Ship service: Go online and find out the rates, print the postage at home, then schedule a free pickup. The problem has been getting out the word that Click-N-Ship even exists, in a world where many small-volume mailers now reflexively call United Parcel Service or FedEx.

"There is, in the younger generation, a sense that the Postal Service is out of date, slow and all the rest," he said. "So reaching them and letting them know that we do provide online services that are useful, customer friendly and timely is a challenge."

Computer-generation technology has also reached 2,000 postal offices nationwide in the form of new Automated Postal Centers, which can do many of the things people stand in line for: dispense stamp sheets, sell postage in any denomination, look up rates and zip codes, provide certified mail receipts, and so on.

Since 2000, the agency has gone through an astonishing makeover of automation and efficiency; reducing staffing by 100,000 to just over 700,000, all through attrition; while delivering more mail to more delivery points. Last year, the post office took roughly 212 billion pieces of mail to 144 million addresses, 2 million more delivery points than in 2004.

What postal officials find most gratifying is that on-time delivery has improved, too: Today, 96 percent of mail is delivered on time to the zip codes that should only take only one day for delivery. Eight years ago, that figure was 92 percent, Day said.

Businesses and other big-volume mailers are bar-coding mail so it can be processed faster and automatically. New optical readers can decipher all but the worst handwriting on envelopes.