THOSE UNUSUAL envelopes bearing the image of a space station that seems to be floating in space have been such a success that the Postal Service is trying the concept again.

This time, however, it is a trio of football players who appear on the hologram that is part of the Postal Service's latest stamped envelope.

The envelopes, which went on sale last Sunday with little advance notice, celebrate professional football. They represent an effort to combine a popular sports theme with the holographic printing technology that proved highly popular with the space station envelope released last year.

Unlike the space station, the latest envelope was produced in secrecy. Produced in cooperation with the National Football League, it went on sale only three days after the internal publication Postal Bulletin revealed it had been produced by the Pennsylvania paper company that produces all the service's stamped envelopes.

The envelopes, which will sell for 30 cents each, were released during the Green Bay Packers' opening game against the Los Angeles Rams in Green Bay, Wis. Postal Service spokesman Jim Murphy said the service selected Green Bay because the envelope shows the NFL's Vince Lombardi Trophy, named after the legendary Green Bay coach whose teams won the first two Super Bowls.

There was no formal ceremony to mark the release and the fans at the game were not given complimentary copies of the envelope as collectors were in Washington last December when the space station envelope was released.

Designed by Bruce Harman of Watsonville, Calif., the new hologram appears on a thin strip of foil paper that is slipped into a window cut in the stamp area of each envelope. Harman's design features three football players dashing in front of a large version of the Lombardi trophy, the prize awarded annually to the winner of the Super Bowl.

Murphy said the service ordered the envelopes after the first hologram envelope proved to be "very, very popular." The first space station printing of 20 million quickly sold out and Murphy said the service is well into the second printing of another 20 million.

That places sales of the space station hologram envelope "head and shoulders above" any other recent stamped envelopes, Murphy said. Officials wanted to market another envelope before next year's rate change and football seemed to be an ideal topic for the fall, he said.

When the space station envelope was released during World Stamp Expo '89, a total of 131,245 were given first-day cancellations, a record for any piece of U.S. postal stationery.

Those envelopes were expected to be such a draw that postal officials deliberately held their release until the last day of the 14-day stamp show, hoping their novelty would attract many collectors to what would have otherwise been a poorly attended day.

Gordon C. Morison, the assistant postmaster general in charge of retail and philatelic sales, is himself a well-known collector of postal stationery and has taken an interest in using postal cards and envelopes to commemorate topical themes and events that used to be celebrated only on stamps.

The latest of those multicolored postal cards -- ones that celebrate the nation's architectural heritage -- will go on sale Sept. 30 at Stanford University. The cards are marking the California school's centennial and the Moorish and Romanesque architecture of the Stanford Quadrangle.

COMMEMORATIVE medals celebrating the 200th anniversary of the Coast Guard are on sale by the U.S. Mint. The bronze medals feature a rendering of Anton Otto Fischer's painting "To the Rescue," which shows a 19th-century rescue boat going across a storm-swept sea to a disabled vessel.

"Guardians of the Sea" is inscribed on a banner across the top of Fischer's scene and the wording "200 years of service" is on the lower portion of the medal.

The medal's reverse side features the Coast Guard seal, the motto "Semper Paratus" ("Always Ready") and the words: "United States Coast Guard." All are superimposed over two crossed anchors.

Three-inch diameter medals sell for $21 and one-half-inch diameter miniature medals are being sold for $2.25. Information is available from the Mint's customer service center in Lanham at 436-7400.

INDIVIDUALS wishing to secure first-day cancellations of the football envelope may either purchase their envelopes locally or by mail at a price of 30 cents each. Collectors who purchase their envelopes should mail them to: Customer-Supplied Envelopes, Football Stamped Envelope, 300 Packerland Dr., Green Bay, WI 54303-9991. Requests for purchase of envelopes should be sent along with an addressed, pressure-sensitive mailing label for each envelope to: Football Stamped Envelope, 300 Packerland Dr., Green Bay, WI 54303-9992. All requests should be postmarked by Nov. 8.

Collectors seeking first-day cancellations of the Stanford postal card should send an addressed mailing label and 15 cents for each card ordered to: Quad at Stanford Postal Card, Stanford, CA 94305-9998. The deadline is Oct. 29.

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