President Bush will ask Congress next week for millions of additional dollars to prevent radiological "dirty bomb" attacks by terrorists, but his proposed budget would also freeze or cut several other key programs aimed at halting leaks of nuclear material and know-how from former Soviet republics, administration documents show.

Energy Department figures released yesterday call for a 30 percent jump in overall spending on initiatives for preventing the spread of weapons of mass destruction -- a threat that Bush described in Tuesday's State of the Union address as the "gravest danger facing America and the world."

Energy Secretary Spencer Abraham, who described the highlights of the plan in a speech, said the proposed increase would be the biggest ever, "proof of this administration's understanding of the tremendous risks posed by proliferating nuclear weapons and materials."

But the proposal drew mixed reactions from nonproliferation groups and weapons experts, some of whom criticized Abraham's description of the spending package as misleading. Budget documents obtained by one group showed that most of the additional dollars -- 84 percent of the $312 million increase -- are earmarked for a controversial domestic program, one that would convert surplus plutonium from U.S. nuclear weapons into commercial nuclear fuel.

Meanwhile, spending on several longstanding programs that improve security at former Soviet nuclear facilities would remain flat or would drop slightly, according to budget figures obtained by the Russian American Nuclear Security Advisory Council (RANSAC), a research group with offices in Washington and Moscow.

"The major increase is to be spent in the United States, while key programs focused on Russian nuclear security have been cut below [fiscal 2003] levels or held to minimum growth," said RANSAC Director Kenneth Luongo, formerly the Energy Department's top nonproliferation official in the Clinton administration. "This is a shortsighted mistake," Luongo said.

Energy Department officials declined to comment on RANSAC's analysis and said the formal budget will be released on Monday.

Among the programs scheduled for funding cuts or freezes is the department's International Nuclear Materials Protection and Cooperation program, the primary initiative responsible for security upgrades for stockpiles of nuclear material in Russia and other former Soviet states, RANSAC said. A bipartisan panel two years ago ranked the safeguarding of Soviet-era nuclear weapons and fissile material as the nation's top security priority.

The nonproliferation experts praised other parts of the proposed budget, including plans to more than double the current $16.3 million in spending on securing radiological material that could be used in making a "dirty bomb," a crude device that uses conventional explosives to spread radioactive material.

Abraham also said that he will propose major funding increases for programs that purchase highly enriched Soviet uranium and that he plans to seek a 33 percent increase in support for the International Atomic Energy Agency, the U.N.-chartered nuclear watchdog.