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 gone in five years.

The department said a decision on production of plutonium-238, reaffirmed last year, "will not be revisited" and that production activities 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 W. 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 current stocks of the unique 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 the isotope 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.