The Bush administration, citing the danger of nuclear terrorism, will announce intensified efforts to retrieve and secure tons of highly enriched uranium scattered among research reactors and repositories around the world.

Decades after the United States and Russia began supplying nuclear fuel abroad, the plan is to spend more money and sharpen the focus of both governments to repatriate it -- "to fill this enormous gap," Energy Secretary Spencer Abraham said yesterday by telephone from Vienna, where he is to announce the $450 million initiative in a speech today.

Accelerating and concentrating existing efforts, Abraham said, the Bush administration will target the "most dangerous, least secure" nuclear materials first. In seeking to convert research reactors in the United States and abroad to less dangerous fuel, the most vulnerable ones will take priority.

Abraham's announcement, months in the making, comes after criticism from outside analysts and the Energy Department's inspector general that the administration has been moving too slowly. Auditors said in February that large amounts of highly enriched uranium produced in the United States "were out of U.S. control."

Just this week, a pair of Harvard University researchers said less fissile material was secured in the two years after Sept. 11, 2001, than in the two years before. The makings of an atomic bomb exist in hundreds of buildings in more than 40 countries, the report said.

Abraham, in Vienna to meet with Mohamed ElBaradei, director general of the International Atomic Energy Agency, intends to acknowledge in his remarks that more must be done.

"We would be fooling ourselves -- and endangering our citizens -- to think that these past efforts are enough," an advance text of his speech says. It describes "the 21st century's greatest conflict" as a battle between "the civilized nations of the earth and the terrorists and terrorist states that would use devastating technologies to destroy them."

The Energy Department intends to remove the uranium retrieval programs from its oft-criticized Environmental Management Program and appoint a coordinator. Nuclear specialists have long said the federal government's nonproliferation programs are too diffused.

Little of the new money projected for the program will be spent soon, a senior Energy Department official said. In the coming 18 months, about $20 million will be added to existing programs, an amount likely to reach $60 million in peak years.

"We will find whatever funds are necessary to get this accelerated," the official said.

Matthew Bunn, co-author of the Harvard report, reacted positively to the administration's plan.

"What's new is pulling these things together, an explicit focus on eliminating the gaps," said Bunn. "If the Abraham initiative is followed through rapidly and flexibly, we have a real chance to get the dangerous nuclear material out of the world's most dangerous sites in a few years."

Beginning in the 1950s, the U.S. government delivered bomb-grade uranium to dozens of countries under the Atoms for Peace program. The idea was to help countries develop peaceful nuclear programs, whether for electrical power or scientific research.

Most of the fuel was to be returned to the United States, either in its most potent form or as spent fuel. Although some has been recovered, many tons of U.S. and Russian fuel remain in distant places.

Under Abraham's plan, all fresh Russian-produced highly enriched uranium would be repatriated by Dec. 31, 2005. Spent fuel would be returned by 2010. U.S.-produced spent fuel in research reactors would be repatriated within a decade, and U.S. authorities will work to convert U.S. and Russian civilian research reactors to safer fuel.