Democratic senators Thursday criticized the administration's budget request for the missile defense program (search), questioning anew whether the system will ever work. Supporters urged continued funding for the program still in development.

Sen. Carl Levin, D-Mich., (searchcalled the request for $10.2 billion "truly staggering" - the largest single-year funding request for any weapon system in history - and questioned the program as "rudimentary and uncertain."

It's double the amount being requested for custom and border protection for the United States, the ranking Democrat on the Senate Armed Services Committee said, asking: "How will this help keep this country safe from terrorist threats we know exist?"

President Bush in late 2002 said that he would begin deploying what he called a limited system to defend the nation against ballistic missiles by 2004.

Though the first parts of the system are to be put into use while more advanced technology is still being developed, Secretary of Defense Donald H. Rumsfeld said at the time that it will likely stop "a relatively small number of incoming ballistic missiles, which is better than nothing."

"How many more billions of dollars should we spend" before knowing whether it will work?" Levin asked Thursday.

Committee Chairman Sen. John Warner, (searchR-Va. countered that this is not the first time officials have been prompted by an "urgent need" to press a weapons system into service while it was still in development.

Warner said the committee should give the program "the strongest of oversight" but also the "strongest of support."

The first missile defenses are expected to go online sometime this fall, with six interceptor missiles in place at Fort Greely, Alaska, plus three more at Vandenberg Air Force Base (search), Calif., by the end of the year, the Missile Defense Agency (search) said.

Their placements reflect the perceived threat of North Korean intercontinental ballistic missiles. The 2005 proposed budget includes money to bring the total number of interceptors to 20.

The request for the budget year beginning Oct. 1 is nearly $1.2 billion - or about 13 percent - higher than last year's.