COLUMBUS, Ohio (AP) _ Self-adhesive stamps are expected to be on the market this summer, but U.S. Postal Service officials say they'll stick to their search for the perfect ''lick and stick'' seal.

Postal officials said last week they plan to test-market a stamp with a peel-off backing as part of their continuing effort to find out why some stamps stick and others don't.

The Columbus-based Battelle Memorial Institute has been researching various moistenable adhesives since last July under a $700,000, 16-month contract with the post office.

It will be the second time the postal service has sold such stamps, said Roxanne Symko, spokeswoman for the U.S. Postal Service in Washington.

A similar attempt in the late 1970s failed because the adhesive simply didn't last very long, she said.

The adhesive stuck well enough in the short run, but philatelists - stamp collectors - complained that the adhesive ate through and destroyed the face of the stamp after only a few months, she said.

Battelle has been asked to find an adhesive formula that will keep stamps affixed to letters as they travel through the high-speed, highly automated postal system. The postal service now uses three types of adhesives on stamps.

Consumers have complained that stamps, which generate $8 billion a year in revenue, often fall off or are shot off letters as they speed through postal machines. Postal officials say the growing volume of mail also has added to the stress placed on stamp adhesives.

Vincent McGinniss, who heads Battelle's sticky stamp research team, said he looks forward to seeing how the self-adhesive stamps work.

''There is room for both types of stamps, although I think 'lick-and-stick' will be around for years to come,'' he said. ''Moistenable stamps will always be around because people view stamps as a traditional thing. It's like motherhood and apple pie.

''The goal is to find the perfect marriage of adhesive and paper to create a superior looking stamp that sticks,'' McGinniss said.