Post offices play a key role in keeping Maine’s islands sustainable. Aside from helping maintain the islanders’ contact with each other and with the mainland, they serve as social centers.

The U.S. Postal Service tries to protect small rural post offices as best it can while cutting back service to deal with reduction in mail use and a mounting deficit. But one of the measures in its two-year reorganization plan discriminates against the island post offices.

Most of Maine’s small post offices are scheduled to have their hours of operation cut to four from the present eight. But there’s an exception for post offices located 25 miles or more away from another post office. They will be operational for six hours a day regardless of their workload, says Tom Rizzo, the National Postal Service spokesman for its northern New England district.

Here’s where the islands are hurt: That exemption doesn’t apply to the two year-round inhabited Cranberry Isles or to Swans Island, Matinicus or Monhegan. Each is within 25 miles of a mainland post office. But a 25-mile trip is a lot harder and more expensive than most 25-mile trips on land. It involves paying for a ferry ride or owning or borrowing a boat.

Any island post office that seeks relief from this 25-mile rule, so it can keep six-hour service, should probably apply first to the postmaster general. Another possibility would be to bring up the matter at one of the community discussion meetings that the postal service plans to schedule in September.

Still another avenue would be to ask for help from Maine’s congressional delegation. U.S. Sen. Susan Collins, R-Maine, interceded last year when the Matinicus Island post office was slated for closing. She obtained a reprieve.

Maine’s islands are a prime asset to the state, but they are vulnerable to change. Fifteen of them still have year-round populations, but some of them are gradually losing residents. On Swan’s Island, two of its post offices have already been closed. If its remaining post office and those on other islands serving as social centers for the islands are cut to four hours, eventual complete closure is probably more likely than if they are on the six-hour list.

The Stamp by Mail program has helped keep some of the island post offices profitable — or at least less unprofitable. Summer residents have been ordering their year-round supply of stamps from their island post office, making its balance sheet look good to postal headquarters.

But, the postal service is discontinuing that program. Summer folks will still be able to buy their stamps in quantity from their island post office, but they must go to the counter instead of getting delivery by mail.

People who want to help keep their island post offices in business will do well to speak up at the September meetings or write letters to the postmaster general or their federal lawmakers.

Maine’s island post offices need all the help they can get.