FEW PEOPLE know as much about the stamps issued by the United Nations as New York lawyer Arleigh Gaines. He has published detailed catalogues listing every stamp and postmark ever used by the United Nations, its subsidiary organizations and the League of Nations, the predecessor of the United Nations.

But when the U.N. Postal Administration asked his advice on how it could produce a new series of stamps to replace its popular series displaying the flags of all the U.N. members, Gaines said he faced one of his biggest challenges.

Last month the United Nations released the second set of six stamps in what will be a five-year series offering Gaines's solution. The stamps use masterpieces of art to honor the Universal Declaration of Human Rights, a U.N. document approved in 1948 which spells out basic rights individuals in all countries should receive.

But the U.N. series could be known as the "potato chip series." Because, like the potato chip in the TV commercials, nobody can get just one of these stamps from the United Nations. You have to purchase a minimum of three of each demonination.

That's because the stamps are printed with connecting tabs that contain the text from one of the declaration's 30 articles. The text is in English, French and German, languages from the three countries where U.N. stamps can be used.

U.N. officials say that the second set of stamps, which went on sale Nov. 16, are proving highly popular despite their relatively high price. It costs $8.12 to purchase the minimum set of 18 stamps, issued at U.N. facilities in New York, Geneva and Vienna.

The United Nations has repeatedly honored the Declaration, releasing a set of commemoratives every five years with a more abstract design hailing the overall document.

"But all of the previous stamps had not gotten into the text of the Declaration and the text is quite significant," Gaines said. The trouble with the idea is that "a stamp with nothing but text is boring."

The United Nations, which has a highly innovative stamp design policy, agreed to Gaines's suggestion to make the Declaration the subject of its next stamp series and to use tabs to print the actual text.

On the stamps themselves, Gaines suggested using great works of art -- sculpture, drawings and paintings. There are 30 stamps planned for the series, one for each article in the Declaration. Among this year's designs are a fragment of the sarcophagus of Plotinus to illustrate the concept of equality before the law, Vincent van Gogh's painting "The Prison Courtyard" for the declaration's ban against abitrary arrest and Charles Paul Renouard's painting of the trial of Alfred Dreyfus for the right to a trial.

Each sheet of stamps in the series contains 12 stamps and 12 tabs, a format that effectively doubles the price of printing the stamps. For that reason alone, Gaines said, "I'd be surprised if they use it again any time soon."

Unlike most U.N. issues, the United Nations will keep all the stamps in the series on sale for five years, allowing collectors to purchase the entire set through 1995.

ROGER DUDLEY of Falls Church must be one of those people that consumer advocate Ralph Nader most detests.

Nader, who has been turning his attention to the Postal Service, says Postmaster General Anthony M. Frank is allowing Post Offices to become knickknack shops. Dudley is one of those entrepreneurs who is promoting the trend.

Last year Dudley, a former stamp collector, convinced the Postal Service that a Christmas tree ornament he designed featuring a Christmas stamp mounted on a silverplated doily, would be a best seller. The service sold 60,000 of them at $12.95 each.

This year the service has ordered 100,000 featuring 1990's two holiday stamps and Dudley says he has come up with a mark -- "like mint marks on coins" -- to make the ornaments more valuable. Each of the ornaments is identified with a code indicating which postal division sold the decoration and the number of ornaments that division ordered. By that standard, the 75 ornaments stamped "LA" and headed for the Los Angeles postal division promise to be the most valuable this year; and the 20,000 with the "HQT" stamp for the postal headquarters in Washington, the least.

THE CRABSTATE Coin and Stamp Expo will be held this weekend at the Sheraton Hotel, 8500 Annapolis Rd., Lanham. Hours are 10 to 7 Friday and Saturday and 10 to 4 Sunday. Admission is free. Call 301/459-8329.

UNITED NATIONS stamps are available from the U.N. Postal Administration, P.O. Box 5900, Grand Central Station, New York, NY 10163. This year's U.S. Postal Service ornaments are selling for $14.95 each and are available at many post offices or by mail from the Philatelic Sales Division, P.O. Box 44997, Kansas City, MO 64133-9997.

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