WASHINGTON — U.S. lawmakers continue to push for an East Coast interceptor site to defend against long-range ballistic missiles, but top Pentagon officials want the Missile Defense Agency to focus on other priorities first.

The current Ground-based Midcourse Defense system, which serves as the primary U.S. territorial missile shield, already has fielded interceptors at sites in California and Alaska to shoot down North Korean missiles. The MDA is studying options for a third site in the eastern United States to counter a potential Iranian missile threat.

But lawmakers and Defense Department officials disagree over how quickly that site may be needed.

Speaking at the Center for Strategic and International Studies here May 19, Navy Adm. Sandy Winnefeld, vice chairman of the Joint Chiefs of Staff, said an East Coast site “could eventually be necessary.”

“The only reason to make that investment would be to provide the capability to shoot, assess and then shoot again,” he said. “We can only do that if we have the sensors we need in order to be able to do so.”

The price tag for an East Coast site is expected to be at least $3 billion.

Winnefeld said he would rather the department invest in target discrimination capabilities and the ability to “see targets at the head of the line.”

Navy Vice Adm. James Syring, the head of the MDA, has said a long-range discrimination radar and improved discrimination capabilities are two of his top three priorities.

Syring and Winnefeld are not alone in downplaying the urgency of an East Coast interceptor site.

“If I had one more dollar to do ballistic missile defense, I wouldn’t put it against the East Coast missile site; I’d put it against those technologies that allow us to get to the correct side of the cost curve in the ballistic missile defense,” Navy Adm. Bill Gortney, commander of North American Aerospace Defense Command and U.S. Northern Command, said during an April 7 press briefing.

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But lawmakers are eager for the Pentagon to break ground on a new installation.

In marking up their versions of the National Defense Authorization Act for 2016, members of the House Armed Services Committee said they would like to see a new field built sooner rather than later. Members of the Senate Armed Services Committee are likewise anxious about how long it might take MDA to bring an East Coast site online.

The House has authorized $30 million for an East Coast site to defend “specifically against long-range ballistic missiles from the Islamic Republic of Iran.”

For their part, the Senate Armed Services Committee asked the MDA to study whether an East Coast site could be operational in three years, rather than the five-year timeline the agency has suggested.

Currently, the MDA is considering four sites: Fort Drum, New York; the Naval Air Station Portsmouth SERE Training Area, Maine; Camp Ravenna Joint Training Center, Ohio; and Fort Custer Training Center, Michigan. The agency expects to complete environmental impact studies on those sites by the middle of 2016.

“The committee is concerned that this timeline may be too lengthy if necessary to react to the deployment of intercontinental-range ballistic missiles in Iran,” report language accompanying the Senate bill said. “In such a circumstance, it would be advantageous to understand if, and how, an additional interceptor site in the United States could be made operational in three years or less.”

But Winnefeld said MDA’s California and Alaska sites already protect the United States from “existing and projected” threats from Iran and North Korea.

“A decision to construct the new site would come at significant material development and service sustainment cost. So we need to be careful,” he said. “In the near-term, upgrading the kill vehicle on the [ground-based interceptor], improving our ability to discriminate, and enhancing the homeland defense sensor network are higher priorities for us.”

Meanwhile, on June 2, the House Appropriations Committee passed a version of the defense spending bill for 2016 that includes $217 million for an improved interceptor. That figure is about $60 million less than the Pentagon had requested. Committee members docked the program for a “lack of justification materials and schedule,” according to report language accompanying the bill.

The bill also includes $52 million for the multi-object kill vehicle, a concept to place several miniaturized kill vehicles atop a single interceptor. The House Armed Services Committee had recommended the agency spend $86 million on the project in 2016.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.