Six more small moons circling Uranus have been identified in pictures sent to Earth by the Voyager 2 spacecraft, doubling the number of moons known to be in orbit around the seventh planet from the sun.

The newly discovered moons range in size from 20 to 30 miles across and appear to be in roughly the same orbit 46,560 miles from Uranus, suggesting that they may have been part of a larger moon at one time. The new moons are outside the orbit of Uranus' nine known rings, and thus not among the 18 "shepherd" moons that scientists expect to find inside the rings. The name "shepherd" derives from the belief of scientists that these moons keep the rings from colliding.

"We still have not discovered any of the moons we predicted in advance," Voyager project manager Ellis Miner said yesterday at California's Jet Propulsion Laboratory, where the flight of Voyager 2 is directed. "So there may be at least an additional 18 moons out there."

Prior to Voyager's flight, Uranus was known to have nine rings and five moons, the latter ranging from 310 to 1,010 miles across. Voyager, on its way to an historic encounter with the planet next Friday, has now found seven additional moons for a total of 12.

Scientists expect to find even more moons and rings around Uranus, in part because the spacecraft, on flights past Jupiter and Saturn in 1979 and 1981, respectively, found previously unidentified rings and moons circling those planets, including tiny "shepherd" moons between Saturn's dazzling rings.

For identification, the seven new moons around Uranus have been given the letter "U" and "1986." It will be years before astronomers agree on names for them.