(Reuters) – Randy Forbes, a key member of the House Armed Services Committee, on Thursday urged Defense Secretary Chuck Hagel to rethink the U.S. Navy’s current plan to allow Boeing Co’s F/A-18 fighter jet production to close in 2016.

Forbes released a December 4 letter to Hagel in which he raised concerns about the fighter industrial base and warned about relying solely on the next-generation F-35C fighter jet being developed by Lockheed Martin Corp since it will not be ready for operational use on an aircraft carrier until 2019.

“The risk to U.S. national security and the health of our aviation industrial base of relying on only one tactical aircraft supply line is simply too great to allow the line to close,” Forbes said in the letter.

The lawmaker’s warning comes amid a concerted push by Boeing for additional U.S. and foreign orders for its popular F/A-18 Super Hornet and the EA-18G Growler electronic attack plane based on the same airframe to keep production going.

Boeing executives say they see good prospects for additional F/A-18 orders from the U.S. Navy, Canada, Australia, Denmark and several other countries, and they plan to continue investing in the fighter line.

Dennis Muilenburg, head of Boeing’s defense business, last month said the company must decide soon whether to self fund certain long-lead procurement items to extend the line beyond 2016, but he did not expect a decision to shut the line.

U.S. Navy officials say they would like to buy more F/A-18s and are exploring options to do so but caution that there is no funding for any such purchases at this point. The timing of any new foreign orders also remains unclear.

Forbes said the Pentagon should maintain F/A-18 production in St. Louis, Missouri to safeguard the industrial base and ensure competition. Shutting the line, he warned, would eliminate “vital competition that could result in spiraling costs, leading to more expensive, less capable systems.”

It would also eliminate competition among suppliers, including companies that build aircraft radar and engines.

Forbes urged Hagel to ensure continued competition in the fighter jet market, just as it has done in shipbuilding and submarine industries.

A Navy official, speaking on background, said the service would “very much like” to order more F/A-18 or EA-18G aircraft, but there was no funding available at the moment.

“The F/A-18 E/F Super Hornet and EA-18G Growler bring unique, proven and exceptional warfighting capability to the Navy and joint forces,” said the official, who was not authorized to speak on the record. “The Navy continues to closely monitor the production lines and evaluate options to meet our strike fighter requirements.”

POTENTIAL ORDER NOTICE WITHDRAWN

Richard Gilpin, deputy assistant secretary of the Navy for air programs, told Reuters last month the Navy was looking at options for buying more F/A-18 jets, but no decisions had been made. U.S. officials are also talking with foreign buyers about orders that could extend production.

The Navy in October flagged a possible order of up to 36 more F/A-18 fighters or EA-18G electronic attack planes in fiscal 2015, but later withdrew the notice on federal procurement website since there is no funding for more planes.

Navy officials say their talks about possible additional purchases of the Boeing fighter do not reflect any wavering of their commitment to the Lockheed F-35 program, since both fighter jets are intended to operate together for decades.

But some F-35 backers worry that the Navy’s proposal to deal with across-the-board spending cuts required under sequestration by pausing production of the F-35 C-model for two years could unravel that part of the F-35 program, especially if the Navy continues to buy Boeing jets in the meantime.

A two-year delay in order could push pack initial use of the F-35C until 2021, said one former Navy official. “At some point, depending on how the F-35 carrier variant and unmanned planes come along, they may just not need the F-35C anymore.”

The $392 billion F-35 JSF, the Pentagon’s biggest arms program, has seen a 70 percent increase in costs over initial estimates and repeated schedule delays, but U.S. officials say the program has made progress in recent years.