Ukraine has asked for upward of 128 U.S.-made 4th generation fighter aircraft, but these are not among the top three priorities that country needs in its war against Russia and the costs of these systems have to be weighed against theses nearer term needs, the Pentagon’s top policy official said on Tuesday.

The sought after fighter jets include a mix of F-15s, F-16s and F/A-18s, Colin Kahl, under secretary of defense for policy, told the House Armed Services Committee (HASC) during a hearing on oversight of U.S. military support to Ukraine.

Regarding the F-16, Kahl said, “It is a priority for the Ukrainians, but it’s not one of their top three priorities.” Ukraine’s top three priorities are air defenses, including the network and interceptors such as Patriot and Stingers, artillery and related fires, and armor and mechanized systems such as tanks, Bradley and Stryker fighting vehicles for maneuver, he said.

Ukrainian President Volodymyr Zelenskyy has asked the U.S. to provide F-16s and some in Congress, including Republicans and Democrats, want the Biden administration to grant his request believing that it will help Ukraine drive Russia out of its territory faster than the current pace of war seems to indicate.

Kahl, and later in the day Celeste Wallander, another Pentagon official, both said the coming months may be “decisive” in the war.

Kahl was responding to a question from Rep. Chrissy Houlahan (D-Pa.), a retired Air Force officer and advocate of getting U.S. fighters to Ukraine, who asked whether the U.S. is training Ukrainian pilots on F-16s in advance of a potential decision to transfer the aircraft to that country. She and former Republican Rep. Adam Kinzinger (Ill.) helped insert language in the fiscal year 2023 National Defense Authorization Act authorizing the U.S. to begin training Ukrainians on manned and unmanned aircraft to include surveillance systems, fixed- and rotary-wing aircraft.

Kahl replied that this training is not currently taking place, noting that, “Our assessment is that a delivery timeline for F-16s, even on the most expeditious timeline, and the training timelines are essentially the same.” There is no time savings to start training before making a decision to supply the aircraft and the timeline is about 18 to 24 months if older model F-16s are supplied with the possibility to “shave a few months off,” he added.

If new production F-16s are to be supplied, it will take three to six years for them to be delivered, he said.

Kahl also said that Ukraine may not get F-16s and instead may end up with a European-made fighter, so “It doesn’t make sense to start to train them on a system they may never get.”

The F-16 is built by Lockheed Martin [LMT].

Rep. Adam Smith (D-Calif.), the ranking member on the committee, said in his opening remarks that in the “best case scenario” with “some operational F-16s,” these could get to Ukraine within a year, maybe eight months if “lucky.” In addition to having the aircraft, pilots and mechanics need to be trained, spare parts available, and the airfields able to accommodate the planes, he said.

“So, we looked at that and we determined that it is not a wise use of the resources that are necessary to win the fight,” said Smith, who was chairman of the committee before Republicans won control of the House in the last election. He also said that the 4th generation fighters would “struggle to survive” in the face of a “ton” of Russian air defenses.

The Biden administration believes it has enough supplemental funding already provided by Congress to meet Ukraine’s defense needs for the rest of 2023. Wallander, assistant secretary of defense for international security affairs, told another House panel that the Pentagon doesn’t have an estimate on the funding that might be requested in a future supplemental for Ukraine.

The Defense Department is reviewing Ukraine’s longer-term defense needs, Wallander told the House Appropriations Defense Subcommittee, which also received DoD testimony on the oversight of U.S. defense spending for Ukraine.

“So, in addition to the current flow of capabilities for the hot war that we’re seeing right now, we need to be thinking about providing Ukraine with a modern defense capability that will be an effective deterrent that will be too great of a challenge for the Russian military,” she said.

Kahl at the HASC hearing said that in there is a “medium to long-term requirement” for Ukraine to have a more modernized air force to defend itself against future Russian aggression.

The U.S. Air Force estimates that in the long-term Ukraine will need between 50 to 80 F-16s to replace its air force, he said. This would cost between $10 billion and $11 billion for F-16 Block 70s or Block 72s, he said. Older model Block 30/32 F-16s would cost $2 billion to $3 billion if 36 aircraft were provided to Ukraine, he added.

The cost of committing to any F-16s in the near-term have to be weighed against the available security assistance remaining for Ukraine under the current assistance package, he said.

“So, these are the trade-offs that we are making in real time,” Kahl said. “Would it make sense to spend $3 billion on a capability that it will arrive a year and a half from now when that $3 billion is needed for Patriot interceptors or more Bradley Fighting Vehicles or more 155-millimeter ammunition or more GMLRS, etcetera, etcetera. And so that’s the trade trade-offs we’re making at the moment.”

GMLRS refers to Guided Multiple Launch Rocket System, which are surface-to-surface munitions the U.S. is supplying to Ukraine.