Closing the Portsmouth Naval Shipyard carries a one-time cost of $448 million that could be recovered within four years without affecting the Navy’s ability to service nuclear submarines, and realigning Brunswick Naval Air Station retains an operational airfield while consolidating patrol aircraft in Florida, the Navy contends.

The report signed by Navy Secretary Gordon England provides the first detailed look at the Navy’s reasoning behind its proposal to close Portsmouth Naval Shipyard in Kittery, Maine, and to remove P-3 Orion and C-130 Hercules squadrons from Brunswick Naval Air Station.

Critics quickly attacked the 192-page report, which a former Portsmouth shipyard commander derided as a veiled attempt to divert work to struggling private shipyards.

“They can make the numbers come out to say whatever they want, and that’s what they’ve done. We truly question the validity of the numbers they’ve released. They’ve fabricated a scenario that envisions excess capacity in Navy shipyards,” said William McDonough, a retired Navy captain who leads a community group lobbying for the shipyard.

Maine Sen. Olympia Snowe said the Navy’s information was not appreciably different from information that was already available. She said her office was still awaiting the Pentagon’s final certified data used to form the basis of its decisions.

“By law the Defense Department has seven days to release that data,” Snowe said Friday. Every day that goes by without it is one day less that we have to build our case.”

The Navy report, released Thursday, contends closing the Portsmouth Naval Shipyard would retain one nuclear-capable public shipyard on each coast while saving $128 million a year once the shipyard was permanently closed. The Pentagon’s net savings over 20 years would be $1.26 billion, the report said.

In the end, the report said, the decision came down to either Portsmouth or the shipyard at Hawaii’s Pearl Harbor. The Navy concluded that there was greater strategic value in Pearl Harbor’s location, and it proposed divvying up Portsmouth’s workload among public shipyards at Pearl Harbor, Bremerton, Wash., and Norfolk, Va.

McDonough conceded the strategic value of Hawaii as a base of naval operations, but he said Friday that it doesn’t matter where the subs are overhauled and refueled.

The other shipyards cannot perform the work as efficiently as Portsmouth, which he contends saves six months and $85 million each time it is selected to do the work. There are currently five submarines undergoing work at Portsmouth.

McDonough also said he anticipates savings to be funneled to private shipyards that build submarines: Electric Boat in Connecticut, and Newport News in Virginia. Those shipyards have been hurt by cutbacks in the Navy’s shipbuilding program.

In Brunswick, the decision to strip all aircraft from Brunswick Naval Air Station would downgrade its status to “Naval Air Facility” while retaining the capability of the only operational active-duty airfield in New England, the report said. The aircraft would be relocated to another Navy base in Florida.

There would be a one-time cost of $147 million that would be recovered within four years; after that, there would be annual savings of $34.87 million, the report said. The savings would total $238 million over 20 years.

The data released Thursday focused on Navy bases, saying the combined economic impact of closing Portsmouth Naval Shipyard and reducing operations at Brunswick Naval Air Station would eliminate more than 13,000 direct and nondirect jobs.

The report did not address the impact of the proposed closing of a Defense Finance Accounting Service center at the former Loring Air Force Base in Limestone. Maine officials have estimated direct and indirect jobs losses of more than 300.

“This is a huge financial hit for the state of Maine and it goes from one end of Maine to the other,” Maine Gov. John Baldacci said Friday. “The impact of this is going to be devastating … I want people to understand the seriousness of this.”

Maine and New Hampshire congressional leaders have been seeking additional information including materials related to future mission capabilities, environmental impact and availability of land for future expansion.

Also, Baldacci opened up the possibility of expanding the regional effort beyond Maine and New Hampshire by acknowledging “an expression of interest by Massachusetts,” where Otis Air National Guard Base has been targeted for closure.

The door is open to a regional approach to overturning base closure recommendations. “We’ll be looking to get support outside of [Maine and New Hampshire],” he said.