ASK MANY U.S. postal executives which country produces the best-looking hand-engraved stamps, and the answer, almost invariably, is Sweden.

U.S. collectors soon will get another chance to judge for themselves and see how the U.S. Postal Service has modified a design by one of Sweden's best-known philatelic designers.

The USPS has announced that its 1988 stamp program will include the first stamp it has issued simultaneously with two other countries.

Sweden has contributed the design for the stamp that it, the U.S. and Finland will issue March 29 to celebrate the 350th anniversary of Swedish and Finnish settlement in North America. The U.S. will issue its stamp, a 44-cent airmail commemorative, in Wilmington, Delaware, the heart of what once was known as "New Sweden."

The U.S. has issued stamps with other countries since 1958, including two with Sweden, a measure of the USPS's respect for Swedish designers.

Joint-issue stamps are becoming a regular part of the Postal Service's stamp program. This year the U.S. has joined with Morocco to issue a similar stamp celebrating our long friendship with that North African country, and the service last week announced a joint issue with Australia January 26 to mark the 200th anniversary of its first European settlement.

The "New Sweden" stamp will take that cooperation a step further, with the U.S., Sweden and Finland all issuing commemoratives based on a design by Sweden's Goran Osterlund.

How the U.S. stamp varies from its European counterparts tells a lot about the current philosophy of stamp design at the Postal Service and shows that, compared to Europe, simplicity holds sway in American design.

Osterlund's European stamps show two settlers bartering with three Indians against a map of the world and another map of "New Sweden." Washington area collectors will be pleased to note that a thin slice of eastern Maryland appears near the stamp's left border.

The American commemoratives will be smaller, with only three figures (a settler and two Indians). They also will omit the goods over which the group is bartering.

All the stamps carry the issuing nation's name and denomination. The Finnish stamps will carry the legend "Finnish Settlement in America 1638-1988"; the Swedish "New Sweden" with the same dates. The U.S. stamps will say "New Sweden, 1638."

The European stamps have another feature that will interest many collectors who have followed the recent controversy over whether U.S. stamp engravers have been secretly etching their names and placing other marks on U.S. stamps. That's a violation of the policies of the Bureau of Engraving and Printing.

A number of foreign countries allow designers and printers to get their names on their stamps, albeit in very, very small type. Both the Swedish and Finnish stamps will carry Osterlund's name and that of the printing firm.

First-day cover details will be announced later and the Postal Service almost certainly will offer the Finnish and Swedish stamps for sale to collectors along with the U.S. commemorative, which is designed for use on overseas airmail letters.

In last week's column I switched the designers of two of the new transportation series stamps. Tom Broad of Chevy Chase designed the 17 1/2-cent racing-car stamp and Lou Nolan of McLean designed the 5-cent milkwagon stamp.

The previously announced booklet of five historic locomotive commemoratives will go on sale October 1 in 10 a.m. ceremonies at the B&O Railroad Museum in Baltimore. Collectors seeking first-day cancellations are advised that the Postal Service will affix only the panel of all five of the stamps to covers at a price of $1.10 each. Self-addressed envelopes should be requested from: Locomotive Stamps, Postmaster, Baltimore MD 23233-9992.

Collectors can purchase the stamps and forward them on covers to: Customer-Affixed Envelopes, Locomotive Stamps, Baltimore, MD 23233-9991. The deadline is October 31.

Bill McAllister is a member of The Post's national staff.