ASPEN, COLO., AUG. 2 -- President Bush said today Iraq's "brutal aggression launched against Kuwait" underscores the need to go slowly in restructuring U.S. defense forces, but promised that the reduced Soviet threat and the easing of East-West tensions will bring about a 25 percent cut in overall force levels by 1995.

Days after the House Armed Services Committee slashed his defense budget requests, Bush continued to lobby for his more limited cuts, saying he remained committed to the B-2 "stealth" bomber, both the rail-based MX missile and a smaller Midgetman missile -- all of which were eliminated by the committee -- and the Strategic Defense Initiative.

"Prudence demands that we maintain an effective deterrent," Bush said in a speech to the Aspen Institute here, "one that secures the peace not only in today's climate of reduced tensions but that ensures that renewed confrontation is not a feasible option for any Soviet leadership."

The president never directly mentioned the battle he and Pentagon officials are waging with Congress over the size of the defense budget, but said the United States would be "ill-served" with a program that is simply "a scaled-back or shrunken-down version of the ones we possess at present."

Bush acknowledged that budget constraints and a changing security climate require sharp cuts in military strength, but said what is needed is "a defense policy that adapts to the significant changes we are witnessing." What is needed now, he said, is an "orderly reduction -- not a fire sale."

Congressional critics argue that Bush has been slow to adapt to the new world and unwilling to acknowledge the severity of the budget deficit's impact on the Pentagon.

The backdrop of the Iraqi invasion of Kuwait offered Bush a timely rationale to argue that the United States must maintain its strength, while adopting to changes in the international political order.

"Even in a world where democracy and freedom have made great gains," he added, "threats remain. Terrorism. Hostage taking. Renegade regimes and unpredictable rulers. In an era when threats may emerge with little or no warning, our ability to defend our interests will depend on our speed and agility."

Speaking before the Senate narrowly approved the continued production of the B-2 bomber, Bush reiterated the administration's position that 75 of the stealth bombers make "strategic sense" as a deterrent into the next century. Further delays, he said, will only add to the cost, already more than $865 million per copy.

Bush said that while the outcome of START talks with the Soviets will determine the ultimate fate of the MX and the Midgetman missiles, it is important to continue with their development because the Soviets have modernized their own strategic missile force.

Although the House Armed Services Committee eliminated both missiles this week, committee chairman Rep. Les Aspin (D-Wis.) said the action was designed to force the administration to choose one because there isn't enough money for both.

Bush said that despite changes in the Soviet Union, it remains "a world-class military power" that continues "to maintain and modernize their arsenal of strategic nuclear weapons."

But he made clear that U.S. military manpower can be sharply reduced because of reduced tensions. He said that by the mid-1990s, it will take the Soviets so long to "return to the levels of confrontation that marked the depths of the Cold War" that the United States will be able to create "wholly new forces" rather than relying on existing units to deter aggression.