President Carter took the helm of a Navy atomic submarine during nearly nine hours at sea today, and came away saying he was impressed with the performance of the USS Los Angeles, her captain, her crew, and the nation's defense capabilities in general.

"I've had a chance to see the submarine operate on both the surface and submerged conditions . . . at top speed and under all sorts of maneuvers," the President said in a 15-minute press conference upon his return.

"I'm very proud of what I've seen . . . it was a very exciting and gratifying experience for me . . .

"I believe with absolute certainly I can say there is no finer ship in the world than this one . . . It's the latest developed by the greatest country on earth."

Rosaylnn Carter, who went with the President, did not say how she felt about the trip. But the President, who served on conventionally powered submarines during his Navy career 25 years ago, seems to have enjoyed it.

Both on departure shortly after 9 a.m. and on return shortly before 6 p.m., he stood on the submarine's bridge, about 20 feet above the water. Hatless when he left, on the way back he wore a gold-lettered cap reading, "Commander in Chief Jimmy Carter."

Carter said it is "very crucial that but friends and our potential adversaries understand that our country is equipped to defend ourselves, to maintain peace, without belligerence or threat, but with a quiet confidence in the skill of our engineers and the skill of our military people."

He said he had witnessed the ". . . superb capabilities of a war machine [WORD ILLEGIBLE]

The President said that during the voyage Adm. Hyman Rickover, whom Carter has praised as one of the most influential forces in his development as a young man, gave him a detailed report on the nation's submarine force and its capabilities.

The crew of the USS Los Angeles, he said, "acted as if I was not there. They didn't stand at attention when I came into their compartments . . . I didn't go aboard to be treated as a high official."

Both he and Mrs. Carter ate with the crew on the long benches of the crew's mess, he said.

Rickover was asked whether he was proud of how his former junior officer piloted his first nuclear submarine.

"Well, it shows that any sailor or officer in the Navy can become President," Rickover said. "It was an encouragement, and I'm afraid we've introduced competitors to President Carter at the next election, because a lot of people are getting the idea that they got a chance too.

"But he did a superb job," Rickover continued. "He actually piloted the ship at the bow and the stern planes while the ship was making high speed. He actually operated the throttle of the (nuclear) plant when it was making top speed."

Carter said he was particularly impressed with "the tremendous safety factors built in."

"We had a chance, I did, to operate the ship at maximum speed, to go from full speed to flank speed with me at the controls, and the ship was maneuvered very violently but very smoothy . . .

"So I think the impression that I got was of a crew and a war machine, the submarine, very carefully designed and operating as its optimum capability. I was, as you can tell, very much impressed. I'm very proud of the captain and crew of this ship."