The post office’s financial problems are complex. Mail volume has been steadily declining, and the agency has been unable to cut its labor costs or reduce services quickly enough to match the fall in revenue. At the same time, the post office faces legal constraints that prevent it from diversifying into new lines of business, and it is also barred from raising postage prices faster than the rate of inflation.

Mr. Berry noted that the Obama administration did support the postal service’s push to recover $7 billion that officials agree was overpaid into yet another pension fund. But he expressed serious reservations about the postal service’s plan to cut costs by moving postal workers into a new, supposedly cheaper health insurance plan.

The two senators most active on postal issues — Thomas Carper, a Delaware Democrat who is chairman of the subcommittee overseeing the post office, and Susan Collins of Maine, who is the ranking Republican on the governmental affairs committee — criticized the Obama administration for not acting more quickly and decisively to address the post office’s problems.

“The proposals put forward by the administration to date have been insufficient,” Mr. Carper said.

Ms. Collins added, “I just don’t understand why the administration doesn’t have a plan to put before us today, given the dire straits that we’re in.”

Several senators from rural states attacked the postal service’s proposals to close many post offices and to end Saturday delivery, saying it would hurt rural Americans disproportionately and would hurt those who rely on mail delivery of prescriptions and newspapers.

Postal officials say a major reason for the postal service’s financial crisis — it has lost $20 billion over the last four years — is a 2006 law requiring the post office to pay an average of $5.5 billion a year for 10 years to underwrite 75 years of health coverage for future retirees. The post office hopes to use much of $50 billion in claimed pension overpayments to cover those annual health care payments.