Despite a history punctuated by cost hikes, schedule delays and technological problems, the F-35 Joint Strike Fighter appears to be too big — and too important — to fail.

The Pentagon temporarily grounded the stealth fighters after an engine caught fire on a Florida runway last month, marking the latest in a series of public setbacks for a program that had been expected to make its much- anticipated international debut this week at the Farnborough Airshow outside London.

On Tuesday morning, the Pentagon announced a “limited return to flight” for the F-35s, but officials later said the F-35 would not make the trip across the Atlantic for the airshow.

While the fighters are returning to the skies, albeit in a limited capacity, the plane’s problems nonetheless continue to raise concerns that at least some of the United States’ eight international partners on the program may rethink their commitment to the F-35 and make it difficult to attract additional partners. The program’s troubled past has made the F-35, the most expensive program in Pentagon history, a lightning rod for criticism both in the United States and overseas.

But Defense officials and key lawmakers continue to stand by the advanced stealth fighter, which will replace older fighters in the Air Force, Navy and Marine Corps fleet.

“In spite of the problems that people are talking about, like the fire and some of the over budget items and all that, there is no longer a choice,” said James M. Inhofe of Oklahoma, the top Republican on the Senate Armed Services Committee.

When the Pentagon decided in 2009 to stop buying the F-22 Raptor fighter jet after 187 planes, the F-35 became the only game in town.

“When they took the F-22 out, this is the only fifth generation fighter we’re going to have,” Inhofe said. “We can’t have another one.”

The military, Inhofe added, should go “full-bore ahead” with the F-35.

The U.S. military plans to buy 2,457 of the planes, with the vast majority going to the Air Force. The cost of developing and buying the planes comes to roughly $400 billion, but operating and sustaining them adds another $1 trillion to the program’s price tag over the next 55 years.

International partners are expected to buy hundreds of the planes, with the United Kingdom alone on tap for 138 F-35s. Over the past several years, however, several countries have trimmed or delayed their purchases of the aircraft. If that trend continues, the price tag for each plane would almost certainly increase.

Last week, Defense Secretary Chuck Hagel expressed his strong support for the F-35 during a speech at Florida’s Eglin Air Force Base, the scene of a June 23 jet fire that ultimately led to the grounding of the entire fleet.

“I believe this aircraft is the future of our fighter aircraft for our services,” Hagel said. “This is as big a project, the F-35, as we have in the Department of Defense. We have a lot riding on this aircraft.”

Hagel defended the plane despite its problems, saying he does not know of a single platform the military has ever designed and fielded that has not gone through some growing pains.

Sen. Jack Reed of Rhode Island, a senior Democrat on the Senate Armed Services Committee, said the engine fire raises questions about what it will take to get the program back on track. But, like Hagel, Reed said these kinds of stumbling blocks are “not unusual in a very sophisticated development program like this.”

During his trip to Eglin, Hagel sat in the cockpit of an F-35 and spoke to F-35 pilots and maintenance chiefs, who said they have “tremendous confidence” in the fighter.

Following the fire, the Pentagon ordered an investigation to determine the cause, as well as additional inspections of F-35 engines. The Pentagon is still determining the root cause of the engine fire.

Another top Pentagon official told the House Armed Services Committee last week that evidence so far points to an individual failure rather than a larger problem — an assessment that, if correct, could bode well for the plane’s return to service.

“There’s a growing body of evidence this may have been an individual situation, not a systemic one,” Frank Kendall, the undersecretary of Defense for acquisition, technology and logistics, said.

The program is getting its first post-grounding test on Capitol Hill this week, as Senate appropriators draft the fiscal 2015 Defense appropriations bill.

“I’m hoping this incident is isolated. We’ve invested a lot of money in it,” Senate Defense Appropriations Subcommittee Chairman Richard J. Durbin, D-Ill., said last week. “It’s the most expensive weapons system in history. By now, we were hoping we would be further along.”

On Tuesday, Durbin’s subcommittee approved the bill, which matches the Pentagon’s request for 34 F-35s next year. The full appropriations committee will consider the bill on Thursday.

By comparison, the House-passed fiscal 2015 Defense appropriations bill (HR 4870) includes $5.8 billion to buy 38 F-35s next year, which is four more aircraft than the Pentagon requested.

Durbin has been cautious about the international fighter program.

Shortly after taking over the gavel of the Defense Appropriations Subcommittee, he held a hearing specifically focused on the F-35, raising concerns about the cost of the program and its track record.

“The Joint Strike Fighter program has had more than its share of problems over the last decade and, quite frankly, its history reads like a textbook on how not to run a major acquisition effort,” Durbin said at the June 19, 2013, hearing.