Given that Israel would want to strike Iran’s four major nuclear sites — the uranium enrichment facilities at Natanz and Fordo, the heavy-water reactor at Arak and the yellowcake-conversion plant at Isfahan — military analysts say the first problem is how to get there. There are three potential routes: to the north over Turkey, to the south over Saudi Arabia or taking a central route across Jordan and Iraq.

The route over Iraq would be the most direct and likely, defense analysts say, because Iraq effectively has no air defenses and the United States, after its December withdrawal, no longer has the obligation to defend Iraqi skies. “That was a concern of the Israelis a year ago, that we would come up and intercept their aircraft if the Israelis chose to take a path across Iraq,” said a former defense official who asked for anonymity to discuss secret intelligence.

Assuming that Jordan tolerates the Israeli overflight, the next problem is distance. Israel has American-built F-15I and F-16I fighter jets that can carry bombs to the targets, but their range — depending on altitude, speed and payload — falls far short of the minimum 2,000-mile round trip. That does not include an aircraft’s “loiter time” over a target plus the potential of having to fight off attacks from Iranian missiles and planes.

In any possibility, Israel would have to use airborne refueling planes, called tankers, but Israel is not thought to have enough. Scott Johnson, an analyst at the defense consulting firm IHS Jane’s and the leader of a team preparing an online seminar on Israeli strike possibilities on Iran, said that Israel had eight KC-707 American-made tankers, although it is not clear they are all in operation. It is possible, he said, that Israel has reconfigured existing planes into tankers to use in a strike.

Even so, any number of tankers would need to be protected by ever more fighter planes. “So the numbers you need just skyrocket,” Mr. Johnson said. Israel has about 125 F-15Is and F-16Is. One possibility, Mr. Johnson said, would be to fly the tankers as high as 50,000 feet, making them hard for air defenses to hit, and then have them drop down to a lower altitude to meet up with the fighter jets to refuel.

Israel would still need to use its electronic warfare planes to penetrate Iran’s air defenses and jam its radar systems to create a corridor for an attack. Iran’s antiaircraft defenses may be a generation old — in 2010, Russia refused to sell Iran its more advanced S-300 missile system — but they are hardly negligible, military analysts say.

Iranian missiles could force Israeli warplanes to maneuver and dump their munitions before they even reached their targets. Iran could also strike back with missiles that could hit Israel, opening a new war in the Middle East, though some Israeli officials have argued that the consequences would be worse if Iran were to gain a nuclear weapon.