WASHINGTON — The U.S. Air Force’s $4.2 billion wish list for fiscal 2022 includes about $1.4 billion to buy 12 more F-15EX fighters from Boeing, helping to narrow a projected gap as the service divests its aging F-15C/D fleet.

More funding for the F-15EX — which includes procurement of 24 conformal fuel tank sets and assorted spares to extend the range of the aircraft — ranked as the top priority and most expensive item on the service’s annual unfunded priorities list, which was delivered to Congress on June 1 and obtained by Defense News.

But the biggest surprise was the conspicuous absence of additional F-35 Joint Strike Fighters.

The services are required to submit unfunded priorities lists to Congress that spell out how they might spend money if the budget top line had been larger. Typically, lawmakers use the lists as a blueprint for making changes to the budget — especially as rationale for adding more expensive items like ships or aircraft.

Over the past several years, the Air Force requested funds for 48 Lockheed Martin-made F-35s in its budget and additional F-35s in its unfunded wish list. But service officials hinted that practice could stop in FY22 as it waits for the upgraded Block 4 version of the jet to be fielded in the mid-2020s.

Instead, the Air Force list puts $360 million into F-35 sustainment. About $175 million of that sum would go toward 20 F135 engine power modules, helping ameliorate a shortage that is “causing aircraft to become not mission capable at increasing rates,” according to the Air Force’s justification for its unfunded priorities.

Congress is usually amenable to boosting aircraft procurement to the levels laid out in the unfunded list, but the Air Force’s planned divestment of more than 200 aircraft in FY22 — including 42 A-10 Warthogs, 47 F-16C/Ds and 48 F-15C/Ds — could make lawmakers even more likely to increase F-15EX procurement.

The Air Force requested funds for 12 F-15EX aircraft and 48 F-35s in its FY22 budget released Friday.

The second biggest chunk of funding on the unfunded priorities list — worth a collective $825 million — would go toward weapon system sustainment and spares needed to keep aircraft flying.

Specifically, the list includes $37 million for U-2 sustainment, including special fuel, U-2 and T-38 trainer maintenance, and a contract extension for the aircraft’s mission-planning cell. The service also added $37 million for five additional spare engines for the EC-37 Compass Call prior to the production line shutdown. The EC-37 is set to replace the legacy EC-130H Compass Call electronic warfare aircraft.

The list adds $377 million to augment the Air Force’s command-and-control enterprise, with funds to accelerate the Three Dimensional Expeditionary Long-Range Radar program and underwrite ongoing procurement, operations and maintenance of Battlefield Airborne Communications Node aircraft.

The Air Force also included $180 million for three major aircraft upgrades and technologies. It requests $86 million for the Advanced Synthetic Aperture Radar Systems program and $38 million for the Large Common Carriage, allowing the program to move into the engineering, manufacturing and development phase.

The list also adds $57 million for the Adaptive Engine Transition Program, which would allow General Electric as well as Pratt & Whitney to finish work on their engine prototypes.

Finally, the unfunded wish list contains about $1 billion for infrastructure, including about $736 million for military construction projects.

Joe Gould in Washington contributed to this report.