The Senate Armed Services Committee opened a hearing Tuesday on the defense portion of Mr. Bush's spending request.
The budget lists 245 billion dollars for military operations in Iraq and Afghanistan, in addition to nearly 500 billion dollars for other Defense Department costs.
The spending plan would cut funding for some government health care and education programs in the United States.
Among international programs, it pledges more than five billion dollars for treatment and prevention of HIV/AIDS worldwide, 300 million dollars for combating malaria, and also assistance for humanitarian and peacekeeping efforts in Sudan.
Reaction to the budget proposal from Democratic Party leaders was swift and negative.
The chairmen of both the Senate and House budget committees said Mr. Bush's spending plan would move the nation in the wrong direction.
Senate Budget Committee chairman Kent Conrad of North Dakota said the president's proposal is, in his words, filled with debt and deception and disconnected from reality.
This is the first time Mr. Bush's budget has faced a Congress in which the House and Senate are controlled by Democrats.
Information for this story is provided by AP and Reuters.