ST. LOUIS (REUTERS).- A fight between the U.S. government and the St. Louis Art Museum over a death mask from ancient Egypt intensified on Wednesday as the government formally demanded the museum hand over the disputed object. The 3,200-year-old mask of Ka-Nefer-Nefer, a 19th Dynasty noblewoman, sits on display in the basement of the museum. The federal complaint contends the mask was stolen from Egypt before the museum obtained it for $500,000 in 1998. The complaint, which included a request for a restraining order preventing the museum from disposing of the mask during the legal proceedings, came a month after the museum sued the government to try to block the seizure of the mask. U.S. Attorney Richard Callahan said the dispute was