WASHINGTON — The Defense Department is expected to finalize a $10 billion arms deal with Israel, Saudi Arabia and the United Arab Emirates next week that will provide missiles, warplanes and troop transports to help them counter any future threat from Iran.

A weeklong visit to the region by Defense Secretary Chuck Hagel will culminate a year of secret negotiations on a deal that Congressional officials said will be second only to the $29.5 billion sale of F-15 aircraft to Saudi Arabia announced in 2010. But the delicate balancing act that was necessary in weighing the differing interests of each nation made it among the most complex ever negotiated.

While one goal was to ensure that Israel continues to field the most capable armed forces in the region to deter Iran and counter a range of threats, it was equally important to improve the capabilities of two important Arab military partners. Another challenge, senior administration officials said, was coming up with a package that could help Israel deal with various security challenges — but devised so it would not be viewed as an American endorsement of accelerated planning by Israel to strike alone at Tehran’s suspected nuclear facilities.

The objective, one senior administration official said, was “not just to boost Israel’s capabilities, but also to boost the capabilities of our Persian Gulf partners so they, too, would be able to address the Iranian threat — and also provide a greater network of coordinated assets around the region to handle a range of contingencies.”