Donahoe said many of the branches at risk of being shuttered could stay open for months. He was interviewed Friday for an appearance on C-Span's "Newsmakers" to be aired Sunday.
"Our date of the 15th is not a date that we're going to make all kinds of changes. It's never been intended to be a shutdown date for anything," he said. "Any changes we make will be incremental over the course of the summer."
The U.S. Postal Service, battered by recession and by the drop in first-class mail, is trying to cut $20 billion in annual costs by 2015. It agreed to keep all branches and processing centers open until May 15 to give Congress time to negotiate a bill to assist it. The Senate this week passed a measure with bipartisan support but the Republican-controlled House has yet to schedule a vote on its version, which cleared the Oversight Committee last fall.
Donahue said it is unclear how many facilities will be closed, though thousands of locations were under review.
"From a post office standpoint, the word closure is a word we're never used. We've said evaluate," Donahoe said. "Closure is kind of an interesting word that's all over the news and gets people riled up and in some cases for no good reason."