President Carter flew home to Georgia yesterday in one of the nation's $117 million doomsday airplanes.

The specially equipped Boeing 747 would zoom into the sky at the first warning of a missile attack and serve as a flying command post for national leaders. The theory is the plane would be essential in such an attack because ground communications might be destroyed.

If the President wanted to order American submarines patrolling the depths to fire their missiles, he could send the order through the ocean by using a wire antenna that trails for five miles behind the airplane.

There is even a red handle on one of the consoles in the plane for cutting off the wire if it gets tangled in practice drills.

The White House said Carter wanted to become acquainted with the Air Force's Advanced Airborne Command Post and requested the demonstration flight. He is the first President to fly in the aircraft.

Aboard the plane yesterday afternoon, Carter told reporters that he hoped the airborne command center would never have to be used and that flying in it was a "very sobering" experience.

"It is a relization of what might occur unless we do assure peaceful relationships with other nations, and the constant, escalating nuclear capability is one that I accept as a major part of my responsibility as President," he said.

"That's why I'm so eager to let our nation know what the existing threat of nuclear war might be. We have a capability and peaceful relationship and there is another demand on me - to reduce in a very carefully balanced way the entire worldwide nuclear threat . . ."

The Pentagon took reporters on a tour Thursday of a sister plane, one of three available for emergency duty. The Air Force has a fourth Boeing 747 command post, which it is fitting with additional gear to hook into communication satellites. The service wants to buy two more planes.

In a war, the flying command post could stay aloft for 72 hours if aerial tankers were available to fuel it. After 72 hours, Air Force briefers said, lubricating oil in the 747's engines would break down, forcing the command post to land.

The flying command post consists of a presidential suite that is comfortable but not luxurious.

The presidential quarters in the blue-and-white, 231-foot-long plane have a two bunk beds. There are two telephones on a brown leatherette-covered desk, including a red one that would encode conversation so that an enemy could not understand them.

The Air Force operates the plane for the Joint Chiefs of Staff. The plane has a conference room with nine blue-and-gray upholstered chairs and a rectangular table. Adjoining the conference compartment is the main briefing room, complete with lectern, microphone and two screens for displaying slides.

Besides a 15-member battle staff and 27-member Air Force Staff, the plane carries two intelligence specialists from the Defense Intelligence Agency. There are 94 seats in the command post, 16 gold pile rug, gold upholstered sofa and reserved for White House officials.

Since war plans call for getting the command post aloft before it can be destroyed, Air Force briefers said there might not be time to get the President aboard. But they said he could relay his orders through the plane from other command posts, including one deep inside the Pentagon and another dug into the side of a mountain near Ft. Ritchie, Md.

The Air Force plans to move all but one of the 747 command posts from Andrews Air Force Base to Strategic Air Command headquarters in Omaha this summer. Some Air Force families who will have to move have assailed this transfer as a waste of money and a sacrifice of security to placate SAC commanders.

The new 747 command post replaces the smaller Boeing 707, which performed the same role. Richard Nixon flew in the older model when he was President.