WASHINGTON — The Energy Department is moving to resume production of plutonium-238 as an energy source for spacecraft and some national-security activities because existing supplies will be virtually gone in five years.

The department said a decision on production of plutonium-238, reaffirmed last year, "will not be revisited" and that production should be consolidated at the government's Idaho National Laboratory to increase security.

A final decision on consolidation is expected later this year by Energy Secretary Samuel Bodman, department spokesman Mike Waldron said yesterday.

But Waldron reiterated that the decision to resume production of plutomiun-238 was made years ago and reaffirmed last year because it has become clear that current stocks of the isotope will be depleted shortly after 2010.

Plutonium-238 is not used for nuclear weapons, but its steady, virtually infinite release of heat during decay makes it valuable as a heat source to produce electricity in spacecraft and for some satellites that are unable to rely on the sun as an energy source. It is many times more radioactive than weapons-grade plutonium-239, however, and ingesting a speck can be fatal.

The United States stopped producing plutonium-238 when it shut the last weapons reactor at the Savannah River complex in South Carolina in the mid-1990s. Instead it has relied on existing stockpiles and a supply provided by Russia that is limited to use by NASA in the space program.

The government has about 87 pounds of plutonium-238 but expects all but 14 pounds to be used by 2010, including about 55 pounds for national-security-related programs.

"These power systems have been used for the past 30 years, and we expect that their need will continue," Waldron said. "Production of plutonium-238 is critical if the United States is to continue its leadership in areas of space exploration and provide for certain classified security operations."

A draft environmental analysis concludes that consolidation of the program at the Idaho research lab would not cause additional health concerns from radiation releases and would have minimal impact on the environment. "The [analysis] clearly shows the environmental impact ... would be far less than resuming production at three sites around the country," Waldron said. Under the plan, activities that otherwise would be at the Oak Ridge facility in Tennessee and the Los Alamos National Laboratory in New Mexico would be shifted to the Idaho site.

Some people in Idaho and Wyoming have raised concerns about resuming plutonium production at the Idaho National Laboratory, about 34 miles west of Idaho Falls. Some fear it would increase cancer deaths, threaten the nearby Yellowstone ecosystem and make the region a potential terrorist target.

"They refused to look at how many dead and diseased Americans would be affected by a terrorist strike at this facility," said Peter Rickards of Twin Falls, about 160 miles west of the site.

Jeremy Maxand, director of the nuclear watchdog group Snake River Alliance in Boise, said yesterday, "Everybody is downwind from the Idaho National Laboratory. There is no safe place to put this stuff."