| 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) |
| LEADS | Law Enforcement Advancing Data and Science Scholars Program |
| 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) |
| LOC | Library of Congress |
| LOCIS | Library of Congress Information System |
| LOCS | Laboratory Outreach Communication System (older link archive) |
| LODES | LEHD Origin-Destination Employment Statistics |
| LogiQ | Logical Qubits program |
| LOP | Legal Orientation Program |
| LP | Laboratory of Pathology | Office of Laboratory Policy (older link archive) |
| LPCS | Land Product Characterization System (unable to verify 1/23; older link archive) |
| LPD | Laboratory of Parasitic Diseases |
| LP DAAC | Land Processes Distributed Active Archive Center (older link archive; archive2) |
| LPO | Loan Programs Office |
| LPR | Lawful Permanent Resident |
| LPS | Laboratory for Physical Sciences (older link archive) |
| LPT | Labeling Policy Team |
| LPVD | Laboratory of Persistent Viral Diseases (changed to LNII) |
| LR2000 | BLM Legacy Rehost System |
| LRBAA | Long-Range Broad Agency Announcement |
| LRGBE | Laboratory of Receptor Biology and Gene Expression |
| LRD | Longitudinal Research Database |
| LRN | Laboratory Response Network |
