The Bush administration is seeking $8.5 million to resume a study by the Energy and Defense departments on the feasibility of a nuclear "bunker buster" warhead, but the proposal is generating opposition in Congress and some leaders are pushing for a broader review of the nation's multibillion-dollar nuclear weapons programs.

Rep. David L. Hobson (R-Ohio), chairman of the House Appropriations subcommittee that handles the $6 billion-plus annual budget of the U.S. nuclear weapons complex, says he wants to raise fundamental questions this year about the size of the U.S. nuclear stockpile and why so many weapons remain on high levels of alert.

"Why are we still preparing to fight the last war?" Hobson asked in a speech last week to the Arms Control Association. "The time has come for a thoughtful and open debate on the role of nuclear weapons in our country's national security strategy."

The Ohio Republican, backed by a bipartisan group of House members, last year killed the nuclear bunker-buster study, a version of which was revived in the budget presented to Congress on Monday after Defense Secretary Donald H. Rumsfeld urged last month that the project be revived as a means to attack hardened deep-underground targets.

Last year, Hobson moved $9 million that the administration sought to do research on "advanced concepts" for nuclear warheads and instead directed the funds be spent to study ways to improve the reliability and lifespan of existing warheads. Calling it research for a "reliable replacement warhead," Hobson planned that it would "challenge the workforce [of the national nuclear laboratories] while at the same time refurbishing some existing weapons in the stockpile without developing a new weapon that would require underground testing."

"Until we have a real debate and develop a comprehensive plan for the U.S. nuclear stockpile and the DOE [Department of Energy] weapons complex, we are left arguing over isolated projects such as the Robust Nuclear Earth Penetrator," as the bunker buster is officially known, he said.

In the president's budget released Monday, the Energy Department sought $4 million to continue its part of the bunker-buster study, which envisions using the warhead now in the B-83 nuclear bomb designed originally by the Livermore Nuclear Laboratory. Previously, a study was also underway at Los Alamos National Laboratory to see whether its B-61 tactical nuclear bomb could be used in a bunker buster.

The Pentagon is seeking an additional $4.5 million next year to work on the hardened, earth-penetrating shell for the warhead, capable of digging into hard cement and even rock before exploding.

With about $16.8 million already spent on the study in past years, the administration projected this week that it would need an additional $14 million to complete the study by 2007. Even then, work could not go forward on developing the bunker buster unless Congress gave specific approval.

Hobson is studying the president's requests, a spokesman said yesterday, and had no immediate comment on the budget.

Two Democratic House members, Reps. Edward J. Markey (Mass.) and Ellen Tauscher (Calif.), criticized the funds for the bunker-buster study when the budget was released Monday.

"The Bush budget request for new nuclear weapons will face tough scrutiny by the Congress and I am hopeful that these requests will again be rejected," Markey said in a statement. Tauscher called the request "a waste of money on a weapon commanders in the field have not asked for, is of highly questionable utility, and may trigger a new global nuclear arms race."

Hobson said he wants Congress to focus on other issues as well, including whether the United States can reduce the number of operational warheads beyond the cuts -- from about 6,000 to 1,700 or 2,200 -- called for in the Treaty of Moscow. "A more robust replacement warhead from a reliability standpoint will provide the stockpile hedge that is currently provided by retaining thousands of unnecessary warheads," Hobson said.