Four sheets of a memorial issue honoring the late President Richard M. Nixon contain printing errors that make them valuable. The 160 stamps contain major errors: Nixon's portrait is printed way off center and, more significantly, the president's name is printed upside down. Collectors call that "an invert" and say the mistake may make the Nixon stamps among the country's most valuable philatelic errors, each worth at least $8,000. The Nixon stamp could rank with a famous upside down biplane stamp printed in 1918 and the more recent upside down $1 candlestick stamp that workers at the CIA discovered in 1986, according to Linn's Stamp News, which disclosed the Nixon error this week. Depending on the age and number of misprints known, the newspaper said the value of inverted U.S. stamps ranges from $225,000 for a 100-year-old stamp celebrating the Landing of Columbus to 15 cents for a 1962 misprint that was reproduced by the millions. Christie's, the New York auction house, said Wednesday it has acquired one of the misprinted Nixon stamps from the Virginia resident who bought them and expects it to sell for between $8,000 and $10,000 during an auction Feb. 1. Citing company policy, the auction house declined to give the owner's name. Christie officials would say only that the individual had purchased the stamps at a Northern Virginia post office and did not notice the misprint until after he had begun to break sheets of the stamps apart for mailing. Brian Bleckwenn, a Christie's assistant vice president and stamp specialist, said he presumed the owner would sell only one of the 160 misprints in an effort "to gauge the market." The Nixon stamps, featuring a portrait approved by the Nixon family, were issued April 26 at the Nixon Presidential Library in Yorba Linda, Calif., but the stamps proved unpopular, with some customers expressing dislike for the president who was forced to resign from office. Some Democratic members of Congress pleaded with Postmaster General Marvin T. Runyon after Nixon's death in 1994 not to issue the stamps, but Runyon said presidential memorial stamps were a postal tradition and approved the stamp. A Postal Service spokesman said Wednesday that postal inspectors were aware of the Nixon errors but said they represented "a quality control problem" rather than deliberate mischief by printers. In any event, Runyon has made clear that he is unlikely to do anything to make stamp errors easily available to the public. Eighty-million Nixon stamps were produced by Banknote Corp. of America, a private printing firm. Bleckwenn said a worker simply turned around a sheet of the stamps that had been imprinted with Nixon's portrait before the sheets were fed into a second press, where Nixon's name was to be added to the stamp in red intaglio type. The stamps were then fed into a perforating machine, which miscut them. About 10 stamps were printed on the margins of the sheets but because those stamps lack the inverted name, they are considered less valuable printing "freaks," the Christie's official said. Inverted, or upside-down, stamps are extremely unusual because most contemporary stamps are printed during one continuous pass through a printing press. Most previous inverted stamps were products of sheet-fed presses in which sheets had to be transferred from one press to another.