Leading Infrastructure for Tomorrow's America Act This bill authorizes appropriations for the nation's infrastructure, including appropriations for: secure broadband internet access, with a prioritization on expanding broadband access in unserved areas; drinking water improvements, such as appropriations for the drinking water state revolving fund and programs for reducing lead in drinking water; the electric power grid, with a focus on grid modernization, security, resiliency, and efficiency; energy efficiency in buildings, including homes and schools; incentives for natural gas distribution companies to improve the public safety and environmental performance of the natural gas distribution system (e.g., pipeline replacements); the deployment of renewable energy systems; the incorporation of clean energy into community development and revitalization efforts; revitalization of brownfield sites (commercial properties that are hindered from reuse or redevelopment due to the presence of a hazardous substance, pollutant, or contaminant); hospital infrastructure, with a prioritization given to projects that include cybersecurity; outpatient health care facilities in the Indian Health Service; and the improvement, renovation, or modernization of the infrastructure at clinical laboratories, teaching health centers, or behavioral health care centers. In addition, the bill reauthorizes funding for: (1) a diesel emissions reduction program for certain diesel vehicles or fleets, (2) ensuring the Strategic Petroleum Reserve is operated and maintained in an environmentally sound manner; and (3) establishing a Southeast Refined Product Reserve to mitigate the impacts of a severe energy supply interruption in the Southeast.