IT PROBABLY won't end the debate, but a ceremony planned for Sept. 28 at the State Department should help U.S. stamp collectors answer what may be the major stamp issue of the 1990s: Can private and foreign printers produce as good a commemorative stamp as the federal government's major stamp printer?

The Postal Service is committed to increasing the number of stamps, especially commemoratives, being produced by private printers. It even has asked foreign firms if they would be interested in some of the work that since 1893 has been the virtual monopoly of the Bureau of Engraving and Printing, part of the Treasury Department.

That's why next Friday's 11 a.m. ceremony in the Dean Acheson Auditorium is noteworthy. The bureau's latest stamps -- a pair of 25-cent commemoratives honoring the Federated States of Micronesia and the Republic of the Marshall Islands -- will go on sale then. So will sets of nearly identical foreign stamps printed by two private printers. The Unicover Corp. of Cheyenne, Wyo., printed a commemorative for the Marshall Islands postal system and London's House of Questa produced sets of three similar stamps for Micronesia

Indeed, the stamps from all three countries are so similar -- all are valued at 25 cents each and bear the same design and typeface -- that collectors are certain to be baffled as to whose stamps are whose.

This time the best clue won't be the name of the country. All the stamps bear both the names of the United States and the former territory that the stamps honor for its new "Compact of Free Association" with America.

The two U.S. commemoratives carry the names of the two former territories in large type in the upper left corner. In the lower right is larger lettering -- "USA 25" -- that signifies that these are U.S. stamps.

The Marshall Islands' single commemorative differs primarily in the location of its value, a large "25c" placed in the upper right, above the nation's flag. In smaller type in the lower left is "United States of America."

Micronesia is issuing three stamps and its stamps appear even closer to the U.S. designs. Its stamps, the two similar to the U.S. pair and a third that carries a view of the U.S. flag and the frigate USS Constitution, have their value in the lower right, as do the U.S stamps. All three Micronesia stamps carry the wording "Federated States of Micronesia" in the upper left.

Frank Thomas, a Postal Service spokesman, acknowledged that the Marshall Island and Micronesia stamps appear to be the most similar to any American stamps recently released with another country. Although the U.S. Postal Service and a foreign postal administration have agreed in the past on a common design for stamps, language and the value of the each country's currency usually make their stamps distinctive. This time that may not be the case, Thomas said.

That's why the different printing processes may prove critical. The U.S. stamps were printed by the bureau using a combination of offset for the overall design and intaglio printing to add the lettering. Unlike either the stamps from the Marshall Islands and Micronesia, the U.S. stamps will be given a layer of phosphorous ink to help the canceling machines locate the stamps as envelopes pass through the machines.

Both House of Questa and the Unicover Corp. used an offset lithography process to reproduce their stamps. How similar the stamps appear to those produced by the Bureau of Engraving will give U.S. collectors a clue as to what may be ahead in the quality of U.S. commemoratives.

Micronesia and the Marshall Islands will not sell their stamps to American collectors through the U.S. Postal Service, as other countries have in most joint issues. The Marshall Islands stamps can be purchased from the Stamps and Philatelic Center of the Marshall Islands, 1 Unicover Center, Cheyenne, WY 82008-0021 and the Micronesian stamps from Inter-Governmental Philatelic Corp., 460 W. 34th St., New York, NY 10001-2320.

Collectors attending the first-day ceremony should arrive early to pass through the State Department's security checks.

INDIVIDUALS wishing to secure first-day cancellations of the U.S. stamps may either prepare their own envelopes with stamps purchased after Sept. 29 at their local post office or request postal workers to affix the stamps on up to 50 envelopes at a price of 25 cents per stamp. Collectors who purchase their stamps should mail their envelopes to: Customer-Affixed Envelopes, Micronesia/Marshall Islands Stamps, Postmaster, 900 Brentwood Rd. NE, Washington, DC 20066-9991. Requests for postal workers to affix the stamps should go to: Micronesia/Marshall Island Stamps, Postmaster, 900 Brentwood Rd. NE, Washington, DC 20066-9992. All requests should be postmarked by Nov. 27.

Bill McAllister is a member of The Washington Post national staff.