WASHINGTON — The financially struggling U.S. Postal Service sought this morning to tamp down concern over wide-scale cuts, revealing it will seek to keep thousands of rural post offices open with shorter hours.

At a news briefing, Postmaster General Patrick Donahoe said the mail agency was backing off its plan to close up to 3,700 low-revenue post offices sometime after May 15. Citing strong community opposition, Donahoe said the agency will now whittle down full-time staff but maintain a part-time post office presence in rural areas, with access to retail lobbies and post office boxes....