The U.S. Postal Service announced Thursday that it will reduce its workforce with layoffs and offers of buyouts and will close seven district offices from New England to New Mexico to help address record losses.

The reorganization, designed to eliminate 7,500 administrative, executive and postmaster jobs this year, came as a commission that is evaluating the Postal Service’s plan to eliminate Saturday delivery concluded that one in four letters would be delayed by not just one but by two days.

The independent Postal Regulatory Commission also said that postal officials underestimated the losses the agency would suffer from handling less mail- and overestimated the cost savings.

Five-day service and a smaller workforce are among the Postal Service’s strategies to become solvent after losses of $8.5 billion in fiscal 2010, the result of declining mail volumes. Projected losses for 2011 are $6.4 billion.

Once buyout decisions aimed at administrative staff are final in April, the agency plans to eliminate the jobs of thousands of postmasters and supervisors, many through layoffs, officials said.

‘Nobody did anything wrong, but we’re a victim of the economy and past legislation,