Top Air Force acquisitions personnel who went to Capitol Hill Tuesday seemed to find friendly support from Congress for restoring cut F-35 buys to the fiscal year 2017 budget.

The service had delayed purchasing five F-35 Lightning IIs that were set for 2017 – a move the service said would save close to $700 million – and dropping the Air Force's buy for the year from 48 aircraft down to 43.

Yet despite hammering the Air Force on the A-10 retirement, RD-180 Russian-made rocket engines, and B-21 bomber contract, lawmakers seemed inclined to agree with top brass that delaying F-35 purchases could hurt national security readiness.

"We cannot afford to assume that the enemy will resemble the threats of recent wars, nor can we assume that future fights won’t require greater numbers of advanced aircraft," said Sen. Tom Cotton, (R-Ark.,) chairman of the Senate Armed Services Subcommittee on Airland. "The current investment strategy is too risky and will prove to only be riskier in the near future."

Cotton said Congress needs to increase the military budget topline to meet modernization needs and bring the F-35 online quickly.

"The eventual retirement of 438 F-15s in fleet, and their replacement by only 177 F-22s with eventual support from the F-35 is a serious gamble," he said.

The delay in purchasing the F-35s is one sign of budget constraints forcing the Air Force to focus on readiness as opposed to modernization, said Darlene Costello, the acting assistant secretary of the Air Force for acquisition.

The service needs "stable and predictable budgets if we're going to build the Air Force that insures the joint force can continue to deter, deny, and decisively defeat any enemy that threatens the United States," she said, adding that any further budget cuts would cause the Air Force to "chase short term requirements at the expense of long range strategic planning."

In addition to the F-35, the senators brought up another topic that seems to reappear every few months: restarting the F-22 Raptor production line.

"A lot of us complained about this back when we decided we were going to be downsizing the F-22, and I think all of you would agree now that probably wasn’t a good idea," said Sen. James Inhofe, (R-Okla.). "Now we’re down to 187 operational F-22s. All we hear about is what a great job they’re doing … I think we all know we don’t have enough F-22s."

Lt. Gen. James "Mike" Holmes, the deputy chief of staff for strategic plans and requirements, said part of the decision on the F-22 was based on an "optimistic" view of the future.

"The department and the Congress made a decision that we would not see a near-peer threat within a number of years, and that judgment also proved to be optimistic," he said. "We've seen both Russia and China develop airplanes faster than was anticipated."

With the Raptor in demand for operations in the Middle East, Europe, and Pacific, lawmakers pushed the generals on the exact cost of restarting the production line.

"Has there been any analysis as to what the actual costs would be to start up that F-22 line with the new systems that are currently available with the F-35?" asked Sen. Mike Rounds, (R-S.D.).

"We have not estimated what it would cost to reopen the line and populate it with more modern technology," said Lt. Gen. Arnold Bunch, military deputy to the assistant secretary of the Air Force for acquisition.

But Bunch said independent cost analysis have estimated it would take billions of dollars to restart F-22 production from contractor Lockheed Martin.

"It's been years, and we viewed it in the light of the balancing act we're already doing between readiness and modernization as something that would be cost prohibitive," the general said.

Holmes said the Air Force is already working on a sixth-generation fighter, which it hopes to develop much more quickly than the time it took to create the F-22 and F-35. That new fighter is likely to incorporate much of the existing technology from the fifth-gen aircraft.

"Because we want to do it faster, and we can't' afford to do another 20 year development program for a host of reasons, we'll try to go with technology that's at a high readiness level now," he said. "It's completely possible, as we get to a requirement, that there may be competitors that bid on a modification of an existing technology or platform like the F-22 and the F-35."