Golan Heights
© Abir Sultan/EPA
Israeli soldiers are seen during a military exercise in Golan Heights, Aug. 21, 2012. Israeli Armed Forces have been conducting maneuvers amid raising tensions in the region.
A smaller U.S. contingent may make it more difficult for the Israeli government to launch a pre-emptive strike on Tehran's nuclear program.

Seven months ago, Israel and the United States postponed a massive joint military exercise that was originally set to go forward just as concerns were brimming that Israel would launch a strike on Iran's nuclear facilities. The exercise was rescheduled for late October, and appears likely to go forward on the cusp of the U.S. presidential election. But it won't be nearly the same exercise. Well-placed sources in both countries have told TIME that Washington has greatly reduced the scale of U.S. participation, slashing by more than two-thirds the number of American troops going to Israel and reducing both the number and potency of missile interception systems at the core of the joint exercise.

"Basically what the Americans are saying is, 'We don't trust you,'" a senior Israeli military official tells TIME.

The reductions are striking. Instead of the approximately 5,000 U.S. troops originally trumpeted for Austere Challenge 12, as the annual exercise is called, the Pentagon will send only 1,500 service members, and perhaps as few as 1,200. Patriot anti-missile systems will arrive in Israel as planned, but the crews to operate them will not. Instead of two Aegis Ballistic Missile Defense warships being dispatched to Israeli waters, the new plan is to send one, though even the remaining vessel is listed as a "maybe," according to officials in both militaries.

A Pentagon spokesperson declined to discuss specifics of the reduced deployment, noting that planning for the exercise was classified. But in an e-mailed statement, Commander Wendy L. Snyder emphasized that the Israeli military has been kept informed of the changes. "Throughout all the planning and coordination, we've been lock-step with the Israel Defense Force (IDF) and will continue to do so," Snyder said.

U.S. commanders privately revealed the scaling back to their Israeli counterparts more than two months ago. The official explanation was budget restrictions. But the American retreat coincided with growing tensions between the Obama and Netanyahu administrations on Israel's persistent threats to launch an airstrike on Iran. The Islamic Republic would be expected to retaliate by missile strikes, either through its own intermediate range arsenal or through its proxy, the Hizballah militia, which has more than 40,000 missiles aimed at Israel from neighboring Lebanon.

In the current political context, the U.S. logic is transparent, says Israeli analyst Efraim Inbar. "I think they don't want to insinuate that they are preparing something together with the Israelis against Iran - that's the message," says Inbar, director of the Begin-Sadat Center for Strategic Studies at Bar-Ilan University. "Trust? We don't trust them. They don't trust us. All these liberal notions! Even a liberal president like Obama knows better."

The U.S. anti-missile systems are important because while Israel has made great strides in creating anti-missile shields that protect its population, it doesn't have enough of them to deploy around the entire country, even with the U.S. aid specifically dedicated to building more (as well as crucial offensive capabilities, such as mid-air refuelers and possibly bunker-busting bombs). That makes the presence of the Patriots - first deployed to Israel during the First Gulf War, when Saddam Hussein fired Scuds toward the Jewish State - and other U.S. anti-missile systems extremely valuable. Austere Challenge was billed by assistant secretary of state Andrew J. Shapiro last November as "by far the largest and most significant exercise in U.S.-Israeli history." A stated goal was to "improve interoperability" between American and Israeli anti-missile systems - which are already significantly linked. The U.S. maintains an X-band radar installation in Israel's Negev Desert, pointed toward Iran and linked to Israel's Arrow anti-missile system.

The radar is extraordinarily powerful, so sensitive it can detect a softball thrown into the air from thousands of miles away. But as TIME reported earlier, only Americans are allowed to see what's on the screens, a situation that likely serves to inhibit any Israeli decision to "go it alone" against Iran, because the U.S. array can detect an Iranian missile launch six to seven minutes earlier than Israel's best radar. Difficult as it may be to imagine U.S. decision-makers holding back information that could save Israeli lives, both by giving them more time to reach a shelter, or their interceptors to lock onto and destroy an incoming Shahab-3, the risk looms in the complex calculus of Israeli officials mulling an attack on Iran.

Inside Israel, reports persist that prime minister Benjamin Netanyahu and defense chief Ehud Barak are determined to launch a strike, and American officials continue to urge restraint. Israeli analysts say Netanyahu wants Obama to send a letter committing to U.S. military action by a specific date if Iran has not acceded to concessions, but the U.S. administration does not appear to be complying. U.S. Joint Chiefs chairman Gen. Martin Dempsey told reporters in London this week that a military strike could damage but not destroy Iran's nuclear capability, and added, "I don't want to be complicit if they choose to do it."