PRESIDENT REAGAN has two contrasting sets of stamps in his desk in the Oval Office -- one set that the State Department does not want American collectors to buy and another that many stamp dealers say collectors should avoid.

Both ostensibly come from developing countries, and both illustrate how domestic politics can affect stamp collectors.

The first set of two stamps in the president's collection is from Nicaragua, a country whose goods -- and stamps -- are banned from commercial sale in the United States.

A White House spokesman said it's likely that Vice President George Bush, who has referred to the stamps in his speeches, gave them to Reagan. They carry a portrait of Lenin, the Russian revolutionary, and are proof positive, both Bush and Reagan have said, that Nicaragua's Sandinista government is firmly in the Communist fold.

The second set of stamps comes from a group Reagan has described as the "freedom fighters" in Angola. These bright yellow stamps, which sell for $15 a set, were a gift to the president from one of the country's most controversial stamp dealers, Marc Rousso of New York.

The four stamps, which Rousso presented to the president in March at a Republican dinner in Washington, supposedly were issued by the UNITA forces fighting Angola's Marxist government. Reagan supports the group and has welcomed their leader, Jonas Savimbi, to the White House.

Rousso, whose stamp promotions have brought him repeated criticisms from other dealers, said Reagan was delighted with the gift.

"I am very proud to have this because in my center desk drawer in the Oval Office I have two stamps that have been there for a long time, and they will contrast nicely with this. They are Nicaraguan stamps -- and they bear a picture of Nikolai Lenin," Rousso said the president told him.

Reagan, however, may be alone in joy. Aside from Rousso, few stamp collectors recognize the "freedom fighter" stamps as anything other than colorful stickers. They aren't valid for mail, and they are not recognized by either the U.S. Postal Service or the Universal Postage Union, the international postage agency.

Designed and printed by a Pompano Beach, Florida printer, the African stamps initially were offered to collectors two years ago through the efforts of the Resistance Stamp Agency Inc., a Palm Beach firm. Rousso said that Resistance was a subsidiary of his New York-based Coach Investments Inc. until two years ago and had helped sell similar "stamps" for the Solidarity movement in Poland and for rebels in Ethiopia.

Rousso does not dispute that his promotions and admitted efforts to boost the prices of stamps have made him controversial. He contends his critics simply are too old fashioned and disputes the widely held belief that the freedom stamps are invalid. In some areas of Angola held by rebel forces, the stamps have been used on the mails, he said.

"Oh, absolutely, in my opinion they are absolutely stamps," he said.

If most collectors are wary of that set of stamps in Reagan's collection, they are jealous of his Nicaraguan set.

Since May 15, 1985, the State Department has said Nicaraguan stamps cannot be imported for commercial sale to collectors.

That is the date the Reagan administration imposed a general trade embargo on "goods or services of Nicaraguan origin." At the State Department, which oversees the ban, "stamps are considered goods," says Paul Wisgerhof, deputy director of the Office of Foreign Policy Trade Controls. That infuriates many stamp collectors. "Most collectors consider it tyranny," says Ken Lawrence, a Jackson, Mississippi collector and journalist.

The United States banned stamps from China for 20 years, only to lift the ban when Richard Nixon went to Beijing, Lawrence says. The embargo has served to boost the prices of Chinese stamps to Americans, Lawrence said.

Stamp collectors are especially upset that conservative politicians have been spreading the Nicaraguan stamps around the country to promote their views about the Sandinista government. Meanwhile, collectors are told that they cannot acquire the same stamps.

"Stamp collectors shouldn't be victims of changing fads in foreign policy, but we are," said Linn's Stamp News, the nation's largest philatelic newspaper.

The only exceptions to the current ban are stamps placed on letters mailed into the United States from Nicaragua and the relatively small numbers brought out of the country by tourists -- hardly enough to satisfy the appetite of collectors.

There's another reason collectors are clamoring for Nicaraguan stamps, Lawrence says. They've already played a key role in American history.

At the turn of the century, when the Senate was debating whether to build a sea-level canal through Nicaragua or a more costly one with locks in Panama, supporters of the Panama route presented each senator with a recent Nicaraguan stamp.

It showed a volcano near the canal route. Shortly afterward, the Senate, perhaps fearful of an eruption, voted for the Panama Canal.

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