Jimmy Carter, steamboat passenger, is a driven man with a common touch and a few odd habits.

He laps up river lore. He insists on jogging daily -- no matter how inconvenient. He's determined to shake every hand and hold every baby in sight. And he says he reads -- just as he does at the White House -- in every spare moment.

"I read in the bathroom, at the table when I'm eating and late at night," he told a group of reporters in a revealing interview last night. "Amy reads at the table. Rosalynn reads at the table. My father was the only member of my family for two or three generations who didn't read at the table."

In an average week, he said, he goes through two or three books. One recent favorite was "The Gemini Contenders," a thriller by Robert Ludlum.

After two days of vacationing and campaigning aboard the Delta Queen, Carter was relaxed and exuberant. It seemed the crowds along the Mississippi River had given him an emotional high.

Carter, usually the most private of public men, gave a rare glimpse into his private life and work habits.Sitting at a wrought iron table, he talked affectionately of U.N. Ambassador Andrew Young and of Billy Carter, the brother who has caused him so many problems. He called his first month in office "the good old days," and said he "can't believe" that people have brought their babies out in the rain to see him on this trip.

When the conversation turned to Congress, and someone noted that Mark Twain once had written that congressmen are a "distinctive native American criminal class," the president said, "He's very perceptive."

Catching himself, he quickly added: "by the way, Mark Twain said that about Congress, not me."

Carter, it turns out, also is an incurable notetaker and diarist. Almost every night, he dictates his impressions of the day's activities. Apparently, not trusting his memory, he records the content of some conversations right after they occur.

"It's amazing how detailed mine [diary] is," Carter said.

He writes letters in long hand and takes pages of notes during meetings. During the Camp David summit meetings on the Mideast last year, his notes of conversations with Israeli Prime Minister Menachem Begin and Egyptian President Anwar Sadat stacked up about three inches.

To many of his fellow passengers aboard the Delta Queen, Carter comes across more like the candidate of 1976 than the president of 1979. They find him open, likeable, very down-home.

"I didn't think we'd be able to get close to him," Charles Kaltmayer, a mailman from St. Louis, said today. "He's just like one of us, and he dresses like one of us."

Carter, like most of the 150 passengers aboard, wears a sport coat and tie to dinner. But most often passengers see him wearing blue jeans and jogging shoes, or gray slacks loose at the waist and a polo shirt.

His daughter, Amy, 11, runs around the deck with a group of young girls she met aboard and plays cards and bingo in the lounge. She's also become quite a politician. She follows her parents into crowds of well-wishers, shaking hands and signing autographs.

Carter does his best to put people at ease. He slips an arm around the shoulders of women and admires their grandchildren. When a man from Milwaukee invited him for a nightcap last night, Carter and his wife, Rosalynn, dropped by the Texas Lounge. The president had a gin and tonic; she had white wine.

And so the trip continues down the Mississippi. Today, after letting the president ashore long enough to jog for 30 minutes, the Delta Queen stopped in this Iowa river city. A band and a crowd of several thousand were there to greet the Carters. The reception was polite, if not overly enthusiastic.

"People are here to see the president of the United States, whether it's Jimmy Carter or somebody else," said Tom Kramer, a retired factory worker.

"He's lost popularity around here. There's no doubt about it," said state Rep. Mike Connally, a Democrat. "There is a general feeling of lack of leadership. He's going to have to get out in front and take some hard stands."

Meanwhile, Connally and many other street-wise politicians in the state quietly hope that Sen. Edward M. Kennedy (D-Mass.) will be lured into challenging Carter. "Teddy Kennedy would be good for the ticket," Connally said. "This is a Catholic, Democratic town. He'd bring out the vote."