NASA says the risk of a nuclear accident will be only slight when it launches an interplanetary satellite containing a plutonium power plant later this year from the space shuttle Atlantis.

In an environmental impact statement published Friday in the Federal Register, the space agency says health and environmental consequences of the "most probable" of accidents - a one-in-10 million chance - would be small.The electric generator, holding nearly 50 pounds of plutonium oxide, will be aboard the Galileo spacecraft scheduled for launch from the space shuttle in October for a two-year study of the planet Jupiter.

According to one estimate, if that amount of plutonium were released into the atmosphere, it would have about 10 times the radioactivity of the Soviet spy satellite that crashed into Canada in 1978. Plutonium is used in nuclear weapons as well as nuclear reactors.

The environmental impact statement calls for public comment over the succeeding 45 days before a final statement is issued.

"An intensive analysis of the proposed action indicates that the possible health and environmental consequences of launch or mission anomalies pose small risks," the statement says. "The accident estimated to be the most probable would pose very small health risks and very small probability of environmental contamination."

A nuclear generator has not been carried aboard a space shuttle before, although the devices have been used on space probes and manned flights to the moon.

Galileo will be released into Earth orbit by the shuttle and boosted toward Venus by an attached rocket stage.