ST. PETERSBURG -- A glass bowl dating from the third century B.C., valued at $500,000, was stolen from the Hermitage Museum, the state and Independent Television news programs reported. Museum workers informed police of the loss Tuesday, but it probably occurred Sunday or Monday. The 15-centimeter bowl, made of glass and gold leaf in the Egyptian city of Alexandria, was kept in a back room, where showcases have no alarms. The museum worker who noticed the bowl was missing at first thought it had been taken out for routine examination by experts, the reports said. The director of the Hermitage, Mikhail Piotrovsky, told Independent Television the museum would alert Interpol, Scotland Yard and international auction houses. According to Hermitage curators, only knowledgeable people could properly appreciate the bowl, and the thieves may have been sent by a private collector. The museum's collection of 3 million pieces, from Egyptian mummies to Impressionist paintings, is in the Winter Palace, the 18th-century residence of Russian tsars which is itself a masterpiece of baroque architecture and interior design. But the museum has outdated security and fire alarm systems, and thieves took advantage of that fact at least twice last year, stealing two valuable china vases and some Roman coins. Last month, the Hermitage signed a $2.5 million contract with the Minnesota-based company Honeywell Inc. to install a better alarm system and artificial climate control.