Connecticut lawmakers are urging Acting Defense Secretary Patrick Shanahan to maintain steady procurement of the F-35 Joint Strike Fighter in the next budget cycle even as the Defense Department signals interest in investing in the F-15X fourth-plus generation fighter.

"We write to express our alarm regarding recent reports that the Department of Defense Fiscal Year 2020 budget request will only include 78 F-35 Joint Strike Fighter jets -- six fewer than projected in last year's forecast numbers," said the letter, signed by Connecticut Democrats Sens. Richard Blumenthal and Rep. Chris Murphy and other members of the Connecticut delegation.

Bloomberg reported this week that the DoD will ask for 78 Lightning II fifth-generation fighters in its 2020 request instead of the 84 projected last year. Citing a source familiar with the request, Bloomberg said the Air Force is on track to buy its scheduled 48 fighters while the service considers the opportunity to buy into Boeing Co.'s new F-15X program. That means the Navy or Marine Corps has scaled back its intended F-35 procurement, Bloomberg said.

The lawmakers are concerned the reduction will slow engine production for the Lockheed Martin Corp.-made F-35. Pratt & Whitney manufactures the jet's F135 engine at facilities in East Hartford and Middletown, Connecticut.

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"The F135 engine is affordable and adaptive, delivering unmatched advances in safety, design, performance and reliability," the lawmakers wrote. "The F-35 program employs over 11,000 Connecticut constituents -- directly and indirectly -- with 78 first-tier suppliers and other statewide suppliers that provide parts to primes."

They continued, "We are prepared to work with our colleagues on a bipartisan basis in the FY 2020 budget cycle to -- once again -- secure full funding for the game-changing F-35 to ensure that our warfighters have the most capable, lethal, and stealth fighter fleet."

The letter to Shanahan comes as the Pentagon is preparing to lay out how the F-15X might fit into its inventory.

Air Force Secretary Heather Wilson told reporters at the annual Air Force Association Air Warfare Symposium in Orlando, Florida, last week that the service needs to boost its fighter inventory but had not expected to do so with the F-15X.

"Our budget proposal that we initially submitted did not include additional fourth-generation aircraft," Wilson said, as reported by Defense News.

"We want to buy 72 aircraft a year," she said. On Feb. 19, Bloomberg said the Air Force will request funding to buy eight F-15X jets.

Wilson confirmed speculation that the procurement was forced on the service. The move will mark the first inclusion of a new F-15 in the Air Force inventory in more than 20 years.

-- Oriana Pawlyk can be reached at oriana.pawlyk@military.com. Follow her on Twitter at @Oriana0214.