WASHINGTON — The Navy is betting $42 billion on a new class of aircraft carriers, the world’s biggest and costliest warships ever, even as the Pentagon budget shrinks and China and Iran arm themselves with weapons to disable or destroy the behemoths.

The Navy says the new carriers — rising 20 stories above the water, 1,092 feet long, moving at 30 knots with almost 5,000 Americans on board — can project U.S. power around the globe.

“A carrier is 4 1/2 acres of sovereign U.S. territory,” said Capt. Bruce Hay, a Navy pilot who helps set requirements for the new carrier. “An aircraft carrier is a piece of America, and we’re going to do what it takes to keep them relevant because a carrier is presence and American resolve all at one time.”

The ships’ rising costs are drawing scrutiny from lawmakers at a time when the military faces cuts in personnel and funding for new weapons. Critics see the new Gerald R. Ford-class carriers as big targets for rival militaries expanding their arsenals of ballistic and cruise missiles, undersea mines, submarines, drones and cyber weapons.

“Our future adversaries are developing a set of capabilities specifically for the purpose of attacking our aircraft carriers,” Mark Gunzinger, a senior fellow with the Center for Strategic and Budgetary Assessments, said.

Although it’s still about five years from entering the fleet, the price tag for the USS Gerald R. Ford, the first carrier in the class being built by Huntington Ingalls Industries, based in Newport News, Va., already has climbed about 18 percent in four years to $12.3 billion, according to Defense Department data.

The Navy is trying to assure lawmakers that it was worth the money to start from scratch designing a new carrier.

With an electromagnetic system to launch aircraft similar to those used to propel roller coasters at Walt Disney World, the Ford-class carriers are designed to send swarms of fighter jets over vast expanses of water to deter potential enemies.

The Pentagon’s revised global strategy, released in January, emphasizes a shift to the waters of the Asia-Pacific region at the same time the Pentagon is moving to cut $487 billion from previously planned spending over the next decade. More than $500 billion in additional defense cuts will be required unless the president and Congress agree on plans to avert the automatic reductions known as sequester that are set to begin in January.

The Navy’s oversight of construction on the Gerald R. Ford, or CVN-78, has drawn criticism as cost overruns of at least $800 million have been disclosed this year. Critics led by Sen. John McCain, a former Navy pilot, say the technologies that set it apart from the Navy’s 10 existing carriers may not work as planned when the carrier is launched and begins testing as early as 2013.

“It’s outrageous, it’s a national disgrace,” said McCain of Arizona, the top Republican on the Senate Armed Services Committee. “They try all these experiments and all these different ideas that they have in the new class of carrier and obviously disregard the cost.”

The Navy should have kept buying the proven Nimitz-class carriers, McCain said. The last carrier in the Nimitz class, the USS George H.W. Bush, was commissioned in 2009.

The number of aircraft regularly launched, or the sortie rate, will increase to 160 a day on the new carriers from 120 a day now on the Nimitz class, according to the Navy. The number of sorties can surge to 270 from 192 on the older carriers.

Dispatching more jets from a carrier doesn’t provide a tactical advantage in an age of precision-guided weapons and Tomahawk cruise missiles fired from submarines, according to Norman Polmar, a naval analyst and author who has been a consultant to secretaries of the Navy.

“Do we need a new class?” Polmar said. “The answer is absolutely not. You want to kill someone’s airfield, you launch 20, 30 Tomahawks, which go farther and are more accurate than planes, and you do not risk pilots.”

While a missile-armed submarine can move alone beneath the sea, a carrier must travel with a strike group that typically includes a guided-missile cruiser, two guided-missile destroyers, an attack sub and a combined ammunition, oiler and supply ship, according to a Navy fact sheet.

The Navy estimates that each Ford-class carrier will cost $27 billion to build and then operate and maintain for 50 years, $5 billion less than its Nimitz-class predecessors, even after the rising costs.

Half the savings will come from design and technology changes that will reduce the number of sailors needed, Rear Adm. Thomas Moore, who runs the Navy’s carrier programs, said in an interview at the Washington Navy Yard. The Ford carriers will accommodate 4,660 personnel, down from 5,922, according to a presentation by Moore.

The Nimitz class was designed in the 1960s “when labor was cheap, and so we used manpower to accomplish all the functions,” Hay, the Navy pilot, said in an interview at the Pentagon. “One guy grabbing a case of soda and going up and down a ladder, well, that is a pretty expensive way to transport material inside this kind of ship.”

Some critics of the Ford class’s rising cost, including McCain, say carriers remain the invaluable, and virtually unsinkable, centerpiece of U.S. naval strategy.

Others say carriers, like wooden men-of-war and steel battleships before them, aren’t as useful as they once were. With the proliferation of drones and satellite imagery, carriers become easier to locate and thus potentially more vulnerable, according to Polmar.

While the Ford carriers are going to be “very formidable,” the ships “may not be able to get close enough to a future enemy that has precision-guided anti-ship cruise and ballistic missiles,” Gunzinger said.

China is fielding DF-21 anti-ship missiles that may force U.S. carriers to operate 1,000 nautical miles or farther from an enemy’s coastline early in a conflict, according to Gunzinger. Carrier-based jets with a heavy load of weapons are designed to strike at about 300 nautical miles without refueling, Polmar said.

China also is developing weapons to attack satellites and computer networks, disrupting long-distance U.S. military sensors and communications networks, Gunzinger wrote in a report last year for the Washington-based Center for Strategic and Budgetary Assessments.

Iran’s arsenal includes ballistic missiles that can reach targets across the Persian Gulf region, Gunzinger wrote. Iranian officials have threatened to use anti-ship cruise missiles, smart mines that can sense their targets and swarms of small, fast-attack craft to exert their control over the Strait of Hormuz and Persian Gulf shipping lanes, he wrote. The strait is about 21 miles (34 kilometers) across at its narrowest point, with the shipping lane in either direction only two miles wide, according to the U.S. Energy Information Administration.

Gunzinger said carriers should be equipped with stealth drones that can be launched undetected from greater distances to find and attack their targets.

The combined cost of three Ford-class carriers would be $42.5 billion, according to the Pentagon’s Selected Acquisition Report published in December.

The $12.3 billion for the first carrier includes about $3.7 billion in design and development.

“You are making a $3.7 billion design investment for a class of ship that is going to be around for 94 years,” Moore said. “This is not like building a Honda. It is probably the most complex piece of machinery that is built in the world.”

Among new or updated equipment on the carrier will be its nuclear power plant, weapons elevators, arresting gear and a dual-band radar, according to Moore.

The launch system by General Atomics will use a moving electromagnetic field to propel aircraft from the deck instead of the steam-driven catapults on earlier carriers. The carrier will have three aircraft elevators, each weighing 120 tons and able to lift two fighter jets at a time, according to Huntington Ingalls.

The Navy is trying to reduce labor hours from 53 million on the first ship to 40 million or less for the third, according to Moore. That would make its cost comparable to the Nimitz class when adjusted for inflation, he said.

“I am absolutely incentivized to drive that cost down as low as possible,” said Mike Petters, Huntington’s chief executive officer. The company stands to lose as much as $194.3 million, more than 40 percent of a potential fee, based on the overruns projected by the Navy.

Huntington Ingalls, spun off last year by defense contractor Northrop Grumman, is working to preserve support for the increasingly costly ships in Washington. The company has a web of suppliers across the country that make the case to Congress each year to protect carrier funding.

From 2005 to 2011, the shipbuilder and its predecessor placed orders of about $3 billion in more than 330 of the 435 U.S. congressional districts, according to the Aircraft Carrier Industrial Base Coalition, a group that says it represents about 400 companies.

“When you have 45 states that provide stuff for the ship, it’s a fairly large job-creator,” said the Navy’s Moore.