Cutting the Pentagon's $8.3 billion request for missile defense spending in 2002 would undermine and delay important research and testing, Defense Secretary Donald H. Rumsfeld said Thursday.

Some lawmakers are pushing for a $1.3 billion reduction in the Pentagon's request for the fiscal year that begins Oct. 1

The $8.3 billion for missile defense is $3 billion more than this year. It is, by far, the largest increase in the Bush administration's defense program from the Clinton administration's.

"If you take $1.3 billion out of some portion of it, it's big," Rumsfeld said. "As a percentage, it's enormous, it's very harmful. It moves everything to the right, it delays things. It causes a change in the program that has been put together" to test a wide variety of missile defense technologies.

Sen. Carl Levin, chairman of the Senate Armed Services Committee, has argued that the Bush administration is keeping Congress in the dark about whether and when it would conduct missile defense research and testing that would conflict with the 1972 Anti-Ballistic Missile treaty. Levin, D-Mich., wants the administration to clarify its intentions before his committee acts on the spending request.

President Bush has said he intends to withdraw from the treaty. Rumsfeld said it is too soon to know when that might happen.

In Senate testimony Wednesday, Rumsfeld said efforts in the Senate to delay the Pentagon's missile defense work would make it harder to strike a deal with the Russians on replacing the ABM treaty with an arrangement that allowed for national missile defenses.

"To the extent the Russians develop a perception that the United States is not interested in going forward in providing defense against ballistic missiles or that we're split on that issue, obviously it's in their interest to not come to any agreements with us," he told a Senate appropriations subcommittee.

At a Pentagon news conference Thursday, Rumsfeld expressed confidence that once both the Senate and House complete work on the 2002 defense budget, they will give the administration the full $329 billion it has requested, including the $8.3 billion for missile defense. The total is $18.4 billion more than Bush proposed in February and $33 billion more than the 2001 budget.

"I have every confidence that we'll end up with our budget," Rumsfeld said. "The truth is, we do need every nickel."