IF YOU want to know how anxious the U.S. Postal Service is to get youngsters interested in stamps, head for San Francisco on June 25. There, under the glare of the lights of ESPN, the sports channel, postal officials will issue four stamps dedicated to what are called "Xtreme sports."

These stamps celebrate BMX racing (bicycle motocross), in-line skating, skateboarding and snowboarding, all relatively new -- and to some parents, inherently dangerous -- sports. The Postal Service describes these sports as "daring, but considered within safe limits for children with appropriate gear, training and experience."

Just to assure its sales staff, the Postal Bulletin, an internal publication, advises postal workers that all four athletes on the stamps who are depicted leaping into space on their boards, bikes and skates are wearing "safety gear appropriate to his or her sport."

All four 33-cent stamps are based on photographs of youngsters in the sports, but since no living person is supposed to have his image on a stamp, the faces of three have been altered with the help of computers to make it impossible to identify them. The fourth figure is a snowboarder who was wearing a mask, which officials figured was good enough to obscure his or her identity.

Avery Dennison printed nearly 152 million of the stamps on gravure presses at its South Carolina plant. They will be sold in sheets of 20 self-adhesives.

The Xtreme sports stamps will be issued at the start of the ESPN X Games in San Francisco, an annual 15-day event that attracts thousands of sports fans with millions more watching on cable TV, an audience that postal officials hope to reach.

If you want a less dangerous form of entertainment, head to San Diego on Thursday. Postal officials there will dedicate four stamps to what the federal agency calls "one of America's most rapidly growing and popular hobbies, freshwater and marine aquarium-keeping."

These self-adhesive 33-cent stamps, featuring popular species of aquarium fish, are the second stamps to be printed with the use of a 650-line screen. That's a process that was used with this year's tropical flower stamps and it gives much better definition to designs than was possible with stamps printed on offset presses with the old, 300-line screens. Banknote Corp. of America produced 141.1 million of the fish stamps at its North Carolina plant.

A more conventional commemorative, a gummed 33-cent stamp that requires licking, goes on sale Friday in Sacramento. This stamp, which was recently revised to include an African American among the four miners, celebrates the 150th anniversary of the California Gold Rush. The discovery of that metal near Sacramento in January 1848 brought thousands of people to the West Coast, transforming communities like San Francisco into bustling cities.

Ashton Potter USA Ltd. printed 89 million of the Gold Rush stamps on offset presses in upstate New York.

POSTMASTER General William J. Henderson is telling postal officials that he will insist that all new stamp requests be channeled through the Citizens Stamp Advisory Committee, the panel that long has advised his predecessors on what stamps to approve. The postmaster general's caution came after the agency disclosed it was placing its stamp program under the supervision of its top lobbyist.

Deborah Willhite, senior vice president for legislative affairs, told reporters that she has no intention of trading stamps for votes on Capitol Hill and will refer all requests from lawmakers to the committee.

ETHEL KESSLER of Bethesda, a stamp design coordinator, was named by Azeezaly S. Jaffer, the manager of stamp services, as the person responsible for the latest stamp printing error. "It was an honest mistake," Jaffer told reporters.

Kessler, who was supervising the agency's new series of international mail stamps, was said to have called a printer and suggested a line of small type be placed under a photograph of the Grand Canyon. But she made the mistake of adding that the line should say Colorado, not Arizona, where the canyon lines the Colorado River.

Fortunately, the mistake was discovered before any of the 100 million 60-cent Grand Canyon stamps were released. All were ordered destroyed and new stamps saying "Grand Canyon, Arizona" were ordered printed.

Kessler, who designed the Breast Cancer semipostal stamp, is "a brilliant designer," Jaffer said. She was only responding to a suggestion that the stamp series needed more information since most of the stamps would be headed overseas where individuals might not recognize the American landmarks featured on the series, he said.

THE NORTHERN Virginia Stamp Festival is Saturday from 10 to 6 and Sunday from 10 to 4 at Tysons Westpark Hotel, 8401 Westpark Dr., McLean. Admission is free. For information, call 703/734-2800.

INDIVIDUALS seeking first-day cancellations of the Gold Rush, Xtreme sports and aquarium fish stamps should purchase the stamps at their local post office and place them on addressed envelopes. These should be mailed in a larger envelope to: Gold Rush Stamps, Postmaster, P.O. Box 9998, Sacramento, CA 95813-9991; Xtreme Sports Stamps, Postmaster, P.O. Box 880066, San Francisco, CA 94188-0066; and Aquarium Fish Stamps, Postmaster, 701 N. Loara St., Anaheim, CA 92803-9991. Requests for the gold rush stamp should be postmarked by July 19, Xtreme sports by July 25, and aquarium fish by July 24.

Next week in this space: Photography columnist Frank Van Riper.

CAPTION: Athletes grab some air, but in proper safety attire, on new stamps.