| LDB | Liver Diseases Branch (older link archive) |
| LDDs | Local Development Districts |
| LDP | Loan Deficiency Payments |
| LDRD | Laboratory Directed Research and Development |
| LE | Law Enforcement (FWS) (older link archive) |
| LEAD | Low-Income Energy Affordability Data Tool (older link archive) |
| LEAF | Low-Energy Accelerator Facility |
| LEAP | (Communities) Local Energy Action Program | Legal, External Affairs and Performance Branch (older link archive) |
| LECC | Law Enforcement Coordinating Committee |
| LECS | Law Enforcement Core Statistics Program |
| LED | Local Employment Dynamics (changed to LEHD) |
| LEDP | Laboratory Equipment Donation Program (unable to verify 8/19) |
| LEEP | Law Enforcement Enterprise Portal (older link archive) |
| LEFG | Law Enforcement Forecasting Group (unable to verify 8/18) |
| LHD | Laboratory of Host Defenses (merged into LCIM) |
| LHI | Leading Health Indicators |
| LHNCBC | Lister Hill National Center for Biomedical Communication |
| LHO | Little Horned Owl program |
| LHOB | Longworth House Office Building |
| LHP | National Landslide Hazards Program (older link archive; archive2) |
| LHS | Learning Health Systems |
| LI | Laboratory of Immunology (changed to LISB) |
| LICI | Laboratory of Integrative Cancer Immunology |
| LID | Laboratory of Infectious Diseases |
| LIDE | Laboratory for Infectious Disease and the Environment |
| LIG | Laboratory of Immunogenetics |
| LIHEAP | Low Income Home Energy Assistance Program (older link archive) |
| LIHTC | Low-Income Housing Tax Credit |
| LIHWAP | Low Income Household Water Assistance Program |
| LINCS | Literacy Information and Communication System |
| LIONS | Legal Information Office Network System |
| LIP | Livestock Indemnity Program |
| LIR | Laboratory of Immunoregulation |
| LISB | Laboratory of Immune System Biology |
| LISD | NOAA Library and Information Services (changed to NCRL) |
