"If we were sending a manned expedition to Venus, we wouldn't know whether to send a paleo-botanist, a mineralogist, or a deep sea diver," said Carl Sagan, noted expert on Venus from the University of California, yesterday.

In an informal talk on the atmosphere and surface of Venus given at the Harvard Observatory, Sagan noted that four theories of the nature of the planet had been held within the last 50 years. The earliest concluded that Venus was a planet shrouded with clouds of water vapor, hiding a surface that was nothing but swampy rain forest.

In the 1920's the opposite view was held, and Venus was thought to be a desert planet scoured by constant sand-storms. In 1950, Donald A. Menzel and Fred L. Whipple suggested that the entire planet was covered with ocean. Some time later, the British astronomer Fred Hoyle postulated instead an ocean of oil.

Modern information, said Sagan, indicates that the surface is not covered with water and that the cloud layer which obscures the surface is most likely frozen water vapor at a height of about 22 miles above the surface. The surface temperature seems to be somewhere in the neighborhood of 622 degrees Fahrenheit.