BAGHDAD—The White House is pointing to a proposed sale of F-16 fighter jets to Iraq as a sign of a deepening security partnership, though delivery of the aircraft is a few years away, and Iraq's fighter pilots are still learning to fly.

That means Iraq will be left with a gap in its defenses after the departure this month of the last U.S. forces stationed in the nation.

Iraqi Air Force chief Lt. Gen. Anwar Amin said Tuesday Iraq's purchase of the fighters, which are made by Lockheed Martin Corp., was a "huge project" that would mean greater security for Iraq.

But the first squadron of F-16s, he added, wouldn't be fully operational until 2015 or 2016. "Building the Iraqi air force is not simple and is not easy," he said, speaking at a news conference in Baghdad.

U.S. defense officials have for months expressed concern that the withdrawal of U.S. forces and aircraft would leave Iraq without advanced aircraft to defend its skies. They advocated keeping some residual presence after 2011 to help assist the Iraqi military. Then in late October, the Obama administration announced it would withdraw all troops, after the Iraqi government refused to agree to Washington's condition that U.S. forces have immunity from Iraqi law.

Iraq's nascent air force operates a fleet of cargo aircraft and surveillance planes, but has limited means to defend itself against external threats.

The sale of F-16s is meant to change that equation. Earlier this month, the Defense Department announced the award of an $835 million contract to supply the Iraqi government with 18 F-16s. During a visit this week to Washington by Iraq Prime Minister Nouri al-Maliki, the Obama administration notified Congress of plans to sell Iraq a second installment of 18 F-16s.

The second batch of aircraft, along with weapons, parts and training, is valued at an estimated $2.3 billion, according to the Defense Security Cooperation Agency.

Deliveries of the F-16s won't begin until 2014, around the same time the first Iraqi fighter pilots finish their training. F-16 pilot training typically takes around two years.

Gen. Amin acknowledged the potential gap, but added: "That doesn't mean that our air will be open to any countries to enter."

Iraq has sizeable ground forces, and some units have modern, U.S.-made tanks and other equipment. And while the U.S. is departing Iraq, it still has an estimated 40,000 troops and sailors in the region, not including Afghanistan.

"The F-16 is obviously a very complex weapons system," said Maj. Gen. Russell Handy, the senior U.S. Air Force representative in Iraq. "It's going to take a while to train pilots."

The F-16 deal is important for another reason: The U.S. military sees it as a way to foster long-term military cooperation with Iraq through shared training.

"When the Iraqi government purchases an aircraft through the foreign military sales program, they are not just purchasing an aircraft, they are purchasing the capability to operate that aircraft for the long term," Gen. Handy said.

The F-16, a supersonic fighter that has been in service with the U.S. military for three decades, is also considered a successful export. Many air forces around the world have acquired the aircraft.

F-16s are just one building block of a modern air force, which requires integrating radars, communications, air-defense weaponry and aircraft, said Richard Aboulafia, an aviation analyst with Teal Group, an aerospace and defense consultancy.

"A country needs some kind of supersonic fighter for air sovereignty," he said. "That's a bare minimum level of air power that allows for a basic air patrol and intercept capability, but it's not the same as having a large fleet of multirole planes that can be tasked with air combat, ground attack, reconnaissance, and other jobs."

The F-16, he added, "is unquestionably the most cost-effective multirole plane available, but just having a small number doesn't allow for a traditional air force."

Col. Steve Burgh, an Air Force adviser, noted that there's another problem: Recruiting and training Iraqi pilots who can speak English, the international language of aviation. "That's one of our biggest challenges right now," he said. "We're working through that. Gen. Anwar [Amin], on his list of priorities, that's right near the top."