IN THE SUMMER of 1988, two U.S. Postal Service officials flew to Havana to discuss with representatives of 23 other nations a proposal for jointly issuing stamps to mark the 500th anniversary of the arrival of Christopher Columbus in the New World.

Fearful that some of the other countries in the Postal Union of the Americas and Spain (PUAS) would be lukewarm to the idea, the Americans did not immediately commit themselves to the PUAS proposal to issue at least two stamps a year during a four-year period. Instead, they said the United States could participate in the first year's issue.

But after all the PUAS countries, except Canada, endorsed the series, the Postal Service consented. Last Friday, in a ceremony overlooking the Grand Canyon National Park, it released the second pair of stamps in an "America" series that will run through 1992.

The stamps released Friday depict the "natural wonders" of the New World at the time of Columbus's landfall. What will probably be noteworthy to most about the first two commemoratives, however, won't be their scenes of a lush, green Carribbean island or the reddish brown hues of the Grand Canyon.

What most Americans will probably remember are the stamps' values. The Grand Canyon stamp is the last 25-cent commemorative that the Postal Service is planning to issue before higher first-class mail rates become effective next year. The 45-cent airmail stamp that accompanies it is also expected to be replaced by a more expensive international mail stamp.

Both stamps were designed by Mark Hess of Katonah, N.Y., and were printed by the American Bank Note Co. using a process described as "quadrant printing." It enabled ABN to print one sheet of the 45-cent airmail stamps along with every three sheets of the 25-cent commemoratives on the same gravure press.

In keeping with the design requirements established by the Havana conference, each stamp carries the lettering "America" in large type along with the cresent-shaped logo of the PUAS. Although the two scenes are different, Hess has added a common element to both stamps, a lone bird, circling in the sky in the upper-right portion of each design.

CANADA, whose aggressive coin marketing campaigns have won a following among many American collectors, has launched a 10-piece coin set featuring Canadian aviation heroes and has joined with five other countries in plans to mark the Olympic centennial with sets of commemorative silver and gold coins.

The Royal Canadian Mint said it will begin the aviation series with a two-coin set that salutes two World War II aviators. John E. Fauquier, commander of Canada's No. 617 "Dambuster" Squadron, and Air Marshall Robert Leckie are featured on the first two $20 silver coins.

The coins, which contain a gold cameo-shaped insert bearing the image of the honored pilot, will sell for $50 each, including shipping to the United States. The entire set is being offered for $410 on a discounted basis.

The coins are the first bimetallic coins Canada has offered and, unlike similar coins other countries have produced, the Canadian Mint notes that its 24-gold carat insert will be visible on only one side of the coin.

In addition to the aviation coins, Canada says it will join with Australia, Austria, France and Greece to salute the 100th anniversary of the Olympics with a set of two silver and one gold coins. The Canadian coins will begin the series in 1992 with coins devoted to the Olympic motto -- "Citius, Altius, Fortius" (Swifter, Higher, Stronger) -- and Greece will conclude it in 1996 with coins marking the first Olympiad in 1896.

The Canadian coins will be in direct competition with the set of three U.S. coins that Congress has approved for 1992 to raise funds for the U.S. Olympic Committee. Since the U.S. coins are for the games being held in Albertville, France, in winter and Barcelona in summer, and not part of a coin program endorsed by the International Olympic Committee, it's unlikely that the U.S. Mint will be allowed to market its coins overseas.

INDIVIDUALS wishing to secure first-day cancellations of the America stamps may either prepare their own envelopes with stamps purchased at their local post office or request postal workers to affix the stamps on up to 50 envelopes. Collectors who purchase their stamps should mail their envelopes to: Customer-Affixed Envelopes, America Series Stamps, Postmaster, 100 Mather Business Center, Grand Canyon, AZ 86023-9991. Requests for postal workers to affix the stamps should be mailed along with payment for the stamps to: America Series Stamps, Postmaster, 100 Mather Business Center, Grand Canyon, AZ 86023-9992. All requests should be postmarked by Nov. 11.

CANADIAN COINS are available from the Royal Canadian Mint, Box 457, Station A, Ottawa, Ontario, Canada K1N 9H3, or call 800/267-1871, ext. 599.

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