Why is The Post surprised that the postal service would eliminate 6:30 p.m. pickups {editorial, June 27}? Doesn't The Post know that the delivery of first-class mail is merely a sideline activity for the postal service?

Anyone who counts the incoming mail knows that once proud U.S. Mail is now primarily a conveyer of advertising material and routine commercial paper. The system is so involved in timely dissemination of unaddressed circulars, giveaway "newspapers," fund-raising appeals, misleading retirement real estate giveaway come-ons, telephone books and routine commercial notices for its preferred customers -- the ones who employ lobbyists -- that it simply can't muster the stamina to serve the needs of individual letter writers or recipients.

The key to this disaster is that services to advertising and other commercial users are priced far below their marketplace value. More and more advertisers find it is much cheaper to dump their stuff in the mail than to insert ads in newspapers. That's possible largely because most of the operating costs get charged to letter writers, even though service to letter writers gets less and less priority.

There are interesting economic and political factors that have bent the postal service to the requirements of special interests. Initially, a case could be made for most of them. But the situation is out of control. The special interests are well organized, and the letter-writing public has no spokesman. The congressional watchdog is so sympathetic to special interests that it is part of the problem rather than the solution.

The Post's editorial indicates there is still a spark of interest in the subject. Perhaps The Post will now pursue the subject as vigorously as it pursues those renegade taxicab drivers.

STANLEY E. COHEN

Bethesda