LOS ANGELES -- The lost city of Ubar, called "the Atlantis of the Sands" by Lawrence of Arabia, has been found in remote southern Oman using pictures taken from the space shuttle Challenger, explorers announced here last week.

Expedition leaders Nicholas Clapp and George R. Hedges speculated the city may have been the earliest known shipping center for frankincense -- a fragrant gum resin harvested farther south -- and possibly was the source of frankincense offered to Jesus by one of the wise men.

Ruins of the oasis city were discovered mostly buried under sand at a well site named Shisr in southern Oman's barren "Empty Quarter."

Since excavation started Dec. 26, researchers have overcome sandstorms and deadly vipers to locate the city's octagon-shaped stone walls, 6- to 8-foot-tall remnants of seven of its eight 30-foot-tall mud-brick towers, various rooms, frankincense burners and thousands of pieces of pottery, Clapp and Hedges said.

Researchers found the city by tracing ancient desert roads detected in pictures taken from several spacecraft, including radar and optical cameras carried by Challenger in October 1984, said Ronald Blom, a geologist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Challenger exploded after liftoff Jan. 28, 1986, killing all seven crew members.

"This is a significant and lasting legacy of the space shuttle Challenger, which supplied the first clues for our search," said Clapp, a Los Angeles filmmaker.

He said expedition archaeologist Juris Zarins, of Southwest Missouri State University, estimated the city may have been inhabited from 2800 B.C. until about A.D. 100 based on pottery found there.

If that proves true, the discovery pushes back the date of the spread of civilization in southern Arabia by a thousand years, Clapp said.

The late T.E. Lawrence, the British World War I soldier known as Lawrence of Arabia, called Ubar "the Atlantis of the sands," after the legendary sunken continent.

According to legend, Ubar -- known as Iram, the "city of towers," in Islam's sacred Koran -- was destroyed during a disaster about A.D. 100 and was buried by sand. Clapp and Hedges said evidence indicates the city fell into a sinkhole created when an underground limestone cavern collapsed.

The city probably had fewer than 100 residents, but was surrounded by numerous campsites marked by pottery, fire pits and charcoal, Clapp said.

"There's a good chance that -- with qualified archaeologists such as these -- we may have found Ubar," said Jon Mandaville, a Middle East history professor at Oregon's Portland State University.

Mandaville said if Zarins's preliminary dating is correct, urban development in the region began about 1,000 years earlier than once thought. The oldest cities in nearby Yemen date to about 1800 B.C. to 2000 B.C., he said.

"What is emerging is a clear image of a flourishing urban civilization" in Oman and Yemen at the same time civilized life existed to the north in Mesopotamia, the cradle of civilization, Mandaville said.

Gus Van Beek, curator of Old World anthropology at the Smithsonian Institution in Washington, said "it's certainly possible" Shisr is Ubar.

"It would mean we have settled occupation . . . earlier and farther south in Arabia than previously known," he said.

But Van Beek said he was skeptical about the possibility an overland frankincense trade existed as early as 2800 B.C. because camels needed for such trade were not domesticated until about 1500 B.C.

Previous efforts to find Ubar in Oman's dunes failed in 1930, 1947 and 1953. The latest search was started in 1981 by Clapp.