A powerful new radio receiver began scanning the sky from the Southern Hemisphere Friday for messages from intelligent life from outer space.

About 100 people gathered at the Argentine Institute of Radioastronomy outside Buenos Aires as the high-tech receiver was switched on at 10:09 a.m. EDT and began monitoring more than 8 million radio frequencies. Nothing was immediately detected."Nobody thinks it's going to get turned on and there will be a, 'Hello, how are you?' sitting there. But this is clearly a significant step forward," said astronomer Carl Sagan beforehand.

The new receiver allows astronomers for the first time to systematically search the part of the cosmos visible from the Southern Hemisphere for radio signals from extraterrestrial beings.

"If we were extremely lucky, and there were some relatively nearby civilization broadcasting us a message, but they were in the Southern Hemisphere, we could have blithely been going on all these year and never heard it," said Sagan, president of The Planetary Society, which set up the receiver.

Although there is no evidence intelligent life exists on other worlds, it is theoretically possible, Sagan said.

"A lot of scientists, the overwhelming majority, expect there's a lot of life and intelligence," Sagan said. "The whole point is we don't know."

Astronomers are anxious to scan the sky from the Southern Hemisphere because they will have access to some of the stars nearest Earth, including those in the heart of our own Milky Way galaxy.

"For the first time, we will be a very capable of searching for extraterrestrial intelligence in the other half of the sky," Sagan said by telephone from Cornell University in Ithaca, N.Y.

The $150,000 META II or Megachannel Extraterrestrial Assay II receiver will complement META I, which has been scanning the Northern Hemisphere's sky from the Harvard-Smithsonian Center for Astrophysics' Oak Ridge Obseratory in Harvard, Mass., since 1985.

"We've sometimes detected some strange signals," said Thomas McDonough, who runs the SETI, or Search for Extraterrestrial Intelligence project, for the Pasadena, Calif.-based Planetary Society.