WASHINGTON — If US President-elect Donald Trump moves forward with trying to supplant Lockheed Martin's F-35 with Boeing's F/A-18E/F Super Hornet, he can expect to find opposition from the Air Force, the service's top civilian said.

Trump made waves in December when — just a day after meeting the Defense Department's F-35 program chief and CEOs from Lockheed and Boeing — he tweeted out that he had asked Boeing to price out a Super Hornet that would be "comparable" to an F-35.

While the president can determine whether to cancel a weapons program or direct the military to start a new one, the Air Force remains a strong supporter of the F-35 program, Air Force Secretary Deborah Lee James told Defense News in a Jan. 5 interview.

"The Air Force does not view the F/A-18 and the F-35 to be substitutable at all," she said. "They fulfill different requirements. They're both fine aircraft, don't get me wrong. But it's fourth generation, and F-35 is fifth generation."

"The leaders of the Air Force will have the opportunity when the time comes to advise the president-elect on this," she added. "But based on everything I know, the two are not interchangeable and the Air Force has not expressed interest in the F/A-18s."

Trump has already met with one such official, the Defense Department’s F-35 program chief Gen. Christopher Bogdan, to discuss the program. While the president-elect has not softened on the F-35 since then, James pointed out that his meetings with Boeing head Dennis Muilenburg and Lockheed CEO Marillyn Hewson may have had an impact on Trump’s tone.

"It’s impossible for me to say" what Trump’s intentions are, she said. "But clearly on that particular day, he did have both the CEOs of Lockheed and Boeing come talk to him about these programs. He did talk about costs. … It certainly would be consistent, I believe, that he is trying to negotiate and trying to see whatever he can do to bring down costs further."

Although the joint strike fighter still is working through challenges, the program has shown progress, said James, who pointed to decreased costs and the service’s declaration of initial operational capability last August.