The heads of a Senate panel grilled naval officials about plans to cancel the Marine Corps’ Expeditionary Fighting Vehicle (EFV) last week, as the House prepares to debate a defense bill this week that calls for scaling back planned work on a replacement vehicle.

The Senate Armed Services Seapower subcommittee quizzed Navy acquisition chief Sean Stackley and Deputy Marine Corps Commandant for Combat Development and Integration Lt. Gen. George Flynn at length about plans to kill General Dynamics’ [GD] EFV on May 18.

Ranking Member Roger Wicker (R-Miss.) was particularly adamant in his questioning, querying how the Navy can know the Amphibious Combat Vehicle (ACV), which it is in the very early stages of planning, will not cost more than the long-delayed EFV, which has been in development since the 1990s.

Navy acquisition chief Sean Stackley said he estimates, in very rough calculations, each new ACV could cost $10 million to $12 million, compared to a nearly $18 million projected price of each EFV.

“But we’re very, very early in the process, with the focus on figuring out, OK, how do we get that cost down further,” Stackley testified.

Wicker argued: “If it turns out it’s a $15 million vehicle instead of $12 (million), it becomes a dicier choice, doesn’t it? And that’s not outside the realm of possibility.”

Stackley argued if the cost were to reach the $15 million range, the Navy would go “back into the requirements to figure out how do we get that cost back down so we can get the quantity that’s needed to perform the mission.”

Still, skepticism remains on Capitol Hill about the Pentagon’s plans, announced in January, to no longer buy 573 copies of the EFV, a long-delayed amphibious tracked vehicle that previously faced technical hurdles. The Marine Corps is communicating with the defense industry now about three replacements vehicle efforts: to develop a new ACV, buy a Marine Personnel Carrier (MPC), and upgrade existing Amphibious Assault Vehicles (AAVs).

Seapower Chairman Jack Reed (D-R.I.) said that “now we see the end of the EFV with uncertainty about the system or systems that will replace that capability.”

Stackley told Reed, in response to his question, that the Navy is not considering keeping around the EFV. And Flynn, similarly, told Wicker he does not support a proposal from General Dynamics for the Marine Corps to still buy EFVs–but a smaller number of 200 vehicles, instead of the 573 previously planned.

“First of all…200 vehicles does not give us the capability to do a two-brigade operation; It falls short in the number of vehicles,” Flynn said. “The other part is, the operation and maintenance cost of those vehicles, it’s not just the procurement cost of the vehicles, it’s also the operation and maintenance cost of the individual vehicles, which was another reason why the decision was made to cancel the program. And then we’d also have the challenge then of having to have them a mixed vehicle fleet with different capabilities.”

Meanwhile, the House is slated to debate a fiscal year 2012 defense authorization bill this week that does not fully endorse the Pentagon’s plans to spend roughly $3 billion to upgrade existing AAVs. The legislation, approved by the House Armed Services Committee (HASC) two weeks ago, restricts the spending of FY ‘12 funds on amphibious vehicle efforts until the Navy conducts an analysis of alternatives for them and submits a detailed report to lawmakers. The HASC’s bill report says it is concerned the Pentagon cannot afford a “comprehensive” upgrade to the AAV and a new ACV program and suggests a “more affordable plan” for making just minor survivability upgrades to the AAV.

The committee also criticizes the EFV-canceling plans.

“The committee remains concerned that the (Defense) Department failed to conduct the proper analysis prior to making the decision to terminate the EFV program,” the bill report states. “The committee has yet to see the detailed analysis that would show one way or the other whether or not other alternatives may have been a more efficient solution rather than terminating the EFV program.”