It’s often called the military’s ugliest aircraft, a snub-nosed tank of a plane that’s nicknamed “Warthog” for its appearance and ferocity. The A-10 Thunderbolt II has been the Air Force’s equivalent of an in-the-trenches grunt for almost 40 years: heavily armed and armored, designed to fly low and take out the enemy at close range.

But now, after the plane’s career has spanned from the Cold War to the conflicts in Iraq and Afghanistan, the Pentagon has proposed retiring the fleet as part of across-the-board cuts in defense spending. Getting rid of the remaining 283 planes would save $3.7 billion over five years, Defense Department officials say, and allow the Air Force to bring in more sophisticated aircraft, such as the F-35 Lightning II, to provide what is called close air support.

Supporters of the A-10 have launched an aggressive campaign to save an aircraft that they say is unlike any other in the history of American aviation, and they rallied Thursday on Capitol Hill to make their case.

The effort has banded together some unusual factions — budget watchdogs, soldiers and pilots, and high-ranking members of Congress from both parties — who fear that cutting the program would weaken defense and ultimately cost taxpayers. The battle is one of the most striking examples of how budget cuts are forcing the Pentagon to make drastic choices as it reshapes the military after more than a decade of war.

“While no one is happy about recommending divestiture of this great old friend, it’s the right military decision,” Gen. Mark A. Welsh III, the Air Force’s chief of staff, told the Senate Armed Services Committee on Thursday. “And it’s representative of the extremely difficult choices that we’re being forced to make.”

The A-10, a slow-flying airplane designed to stay close enough to the ground for pilots to be able to distinguish friend from foe, often with their own eyes, has saved hundreds of lives in Iraq and Afghanistan. And it has performed in a way that modern planes — flying high and fast — never could, supporters say.

“The best close-air-support platform we have around is the A-10,” Sen. Kelly Ayotte (R-N.H.) said at a news conference Thursday, at which she was joined by Sen. John McCain (R-Ariz.) and several A-10 pilots. “And we owe it to our men and women in uniform to ensure that they have the best when it comes to this incredibly important mission.”

The A-10 is beloved not just by pilots but also by ground troops under fire who equate the high-pitched whine of the airplane and the roar of its Gatling-type cannon with salvation. In recent congressional hearings, it has gotten rave reviews, particularly by the Army brass.

“The A-10 is the ugliest, most beautiful aircraft on the planet,” said Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff.

“It’s a game-changer,” said Gen. John F. Campbell, the Army’s vice chief of staff. “It’s ugly. It’s loud, but when it comes in and you hear that pffffff [of the cannon], it just makes a difference.”

Flying low and slow

It flies so low and slow that pilots expect to get hit. But that’s what the A-10 is designed for.

Its twin engines are perched away from the fuel and high on the fuselage. The pilot is surrounded by a “titanium bathtub” and bulletproof glass.

But the most striking feature of the A-10 is the 30mm cannon that sticks out of the front of the aircraft like a snake’s tongue. The A-10 is really just a gun that can fly, some say.

“We can kill everything on the battlefield. The full spectrum — tanks to troops,” said William Smith, a retired Air Force lieutenant colonel who flew the A-10 in Iraq and Afghanistan. “The airplane was designed to take a ton of punishment.”

The A-10 was developed in the late 1960s and early 1970s, when helicopters supporting ground troops in Vietnam were being shot down by the dozen. A new one hasn’t been built in 30 years. With the military focusing on high-tech, computer-laden planes that can take off and land vertically, the A-10 is a throwback that looks more like a flying Stude­baker.

It earned its tough reputation during the 1991 Persian Gulf War, taking out much of Iraq’s tanks, artillery and missile sites. It has also been a mainstay of the recent conflicts, flying over rugged terrain to support ground troops, at very low speeds and altitudes lower than downtown office buildings.

Last year, two Maryland Air National Guard pilots were awarded the Distinguished Flying Cross with Valor for their part in a mission that saved 90 coalition troops who were on the verge of being overrun by Taliban fighters in a valley in eastern Afghanistan.

The weather was horrible — drenching rain — and so was the visibility. After talking to the troops on the ground, Lt. Col. Paul C. Zurkowski fired a rocket from his A-10 into the ridgeline where the enemy had hunkered down. He was hit by enemy fire — although he didn’t know it — and made another pass, and another, emptying his gun into the ridgeline until he had fired more than a thousand rounds. Finally, running low on fuel, he returned to base.

A few minutes later, when Maj. Christopher Cisneros, his wingman, arrived, he could tell the troops on the ground were in real trouble. They were “danger close,” calling in fire virtually on top of themselves, knowing there was a chance they could get hit as well.

“They didn’t have a lot of time left,” Cisneros said. “They were at the point where they were being overrun.”

So Cisneros led a formation of three A-10s in low over the valley, firing until the troops could break free and helicopters could come in to evacuate them. Three coalition troops were wounded, but none was killed.

Earlier in the war, Smith, the retired lieutenant colonel, was scrambled to a point in eastern Afghanistan where U.S. forces were taking fire. He guided his A-10 into the valley where the soldiers had been fighting and could see a cave on a ridgeline.

“And in the cave I can see the glow from my night-vision goggles of what appears to be a cooking fire,” Smith said in a recent interview.

He radioed the coordinates to the troops on the ground, who told him to blow up the cave. But Smith refused, saying a cooking fire wasn’t enough evidence to fire into the hillside, potentially causing an avalanche of rocks to fall on the village below.

Instead, he flew in close again and again, banking the airplane so that he could look at the cave with his own eyes. By now the sun was coming up, and as he made another pass, people came out of the cave waving. “There were old people, middle-aged people, and there were children,” he said. “It was obviously a family.”

‘Hard choices’

Air Force officials argue that with the defense spending cuts that have been ordered, they have no choice but to get rid of the entire A-10 fleet. Welsh, the Air Force chief of staff, told the Senate Armed Services Committee on Thursday that officials looked at ways to save the A-10 by cutting other programs. But they ultimately decided that grounding the A-10 was the option with the lowest risk.

“The budget picture we’re presenting to you today is hard choices, nothing but hard choices,” Air Force Secretary Deborah Lee James told the committee. She called the A-10 a “wonderful aircraft. But there are other aircraft that can cover that very sacred combat-air-support mission.”

Welsh said the Air Force must be prepared for “a full-spectrum fight” that involves many missions in addition to close air support.

“The comment I’ve heard that somehow the Air Force is walking away from close air support, I must admit, frustrates me,” he said. “It’s a mission, not an aircraft. . . . And we do it better than anyone.”

One of the aircraft to replace the A-10 will be the F-35, officials have said. But the aircraft, beset by repeated delays and skyrocketing costs, is not expected to be ready until at least 2021. And the Air Force is planning to finish phasing out the A-10s by 2019.

Ayotte, whose husband was an A-10 pilot, called that a dangerous gap. She has led the fight in Congress to keep the A-10, inserting language in the defense spending bill that prevents the Air Force from taking steps to retire the A-10 before the end of 2014.

In his comments at the news conference, McCain was more blunt.

“We are going to do away with the finest close-air-support weapon in history?” he said. “And we are then going to have some kind of nebulous idea of a replacement with an airplane that costs at least 10 times as much — and the cost is still growing — with the F-35? That’s ridiculous. That’s absolutely ridiculous.”

Supporters also noted that this is not the Air Force’s first attempt to get rid of the A-10 so that it could focus on more advanced aircraft.

A 1988 report from Congress’s nonpartisan investigative arm, now known as the Government Accountability Office, said it had been tasked to look into the viability of the A-10 because “the Air Force is concerned about the A-10’s ability to support the Army and survive the Soviet air defense threat of the 1990s and beyond.”