Implementing a federal budget is a lengthy process.  It takes several rounds of negotiations between agencies, the Administration, the House and the Senate.  Many competing interests are involved, and there is no committee or separate item for research. Instead, over 10 legislative committees and several agencies have jurisdiction over some aspects of research. The following links contain budget information relevant to agricultural research and development.
Budget System Concepts and Glossary -pdf

American Association for the Advancement of Science
     Research and Development FY 2004

US Department of Agriculture
      USDA FY 2004 Proposed Budget
      Agricultural Research Service (USDA)
         Research, Education and Economics 2004 Budget
      Economic Research Service (USDA)
          Farm Bill 2002 Provisions and Economic Implications
     Cooperative State Research, Extension and Education Service
          FY 2003 Appropriation and FY 2004 Proposed Budget

Department of Defense
     FY 2004 Budget Materials
     Defence Advanced Projects Agency Budget

Department of Energy
     FY 2004 Request
     Office of Budget

Environmental Protection Agency
     Budget and Performance Plans

National Science Foundation
     Budget, Finance and Awards Management

National Oceanic and Atmospheric Administration
     Research Budget FY 2004
     Budget Office

National Air and Space Administration
     Budget and Management Information