Arthur Schlesinger, the historian, has this theory.

"There is a cyclical rhythm in polities," he says. "Action, passion, then they get worn out. The American people are tired now. They need a rest . . . . Emerson said that politics are largely physiological, it's vitality versus exhaustion. The country gets tired, it needs repose."

Schlesinger is sitting in his East Side Manhattan townhouse, puffing tranquilly on a cigar.

He is so philosophical, so calm this morning that it is hard to imagine that this man was once one of the most energetic senior advisers to one of the most vital presidents in history, Jack Kennedy. s

Outside, through the back window of Schlesinger's living room, where neighboring gardens meet, lies Pat Nixon, in repose in a chaise longue, playing with her towheaded grandchild while her daughter Tricia, in a summer dress and pearls, chats quietly with her mother.

Richard Nixon is nowhere in sight, but his image hovers over these two townhouses as one is reminded of his activist years and the passions that both his and the Kennedy administrations aroused. The memories evoked this hot August morning of those emotional years make it easier to understand what is going on across town in Madison Square Garden.

Schlesinger settles comfortably in his green velvet sofa, the French maid serves coffee, the soft breeze blows in the garden, the Nixon granchild coos playfully.

"Depending on whether it's an activist or an exhausted stage," Schlesinger is saying, "you get a president who responds . . . . The activists got Teddy Reoosevelt, FDR, Kennedy and Johnson.When the country had had enough of activism they got Harding, Coolidge, Hoover, Ike, Ford and now Carter. They are the people who respond to those movements . . . . When a country is in the doldrums you're going to have a doldrum presidency . . . . We're becalmed, this country. But there's so much trouble it's a spurious calm." Parable of the Pig

Doug Doerzman, a delegate from Fort Dodge, Iowa, has a friend named Alphonse Wegmeuller who raises pigs. It seems that Alphonse has an old sow who finally gave birth to 11 little piglets, a lucrative event for any farmer. But then tragedy struck. The sow rolled over in her sleep one night and crushed seven of her little piglets to death. "I wrote a letter to Jimmy Carter," Alphonse told Doug Doerzman, "and I said where were you when it happened?"

Doerzman, a rather heavy-set, middle-aged man, is standing in the middled of the crush of delegates and reporters who are cruising the convention floor trying to find something interesting going on. He is telling this story to explain why he is for JimmyCarter, his point being that you just can't blame the president for everything that has gone wrong. His voice hardly rings with enthusiasm when he talks about the president, although he describes himself as a "pretty hardcore Carter person" . . . "unless some knight in shining armor comes riding down the Avenue of the Americas . . . . I guess we're here on a faith visit. Maybe it's a hope thing again but that's a terrible thing to say. I really think we've lost this thing called hope. We're in such a negative situation . . . we're going to hell y'know." The Glamor That Was

Over at the Shubert Theatre, a group of Kennedy supporters is rehearsing for a fund-raiser to pay off campaign debts. It is called "Broadway for Kennedy," an evening with composers and lyricists -- with Lauren Bacall as the host, Peter Stone the producer, Lenny Bernstein, Adolph Green and Betty Comden, Jule Styne, Cy Coleman and others participating. g

Cy Coleman is playing one of his songs, "Hey Big Spender, spend a little time with me," which he has announced is Billy Carter's song to Qaddafi, while Betty Bacall dances playfully around the stage.

There is an air of electricity about the group assembled in their summer jeans and T-shirts to put on a show. They are the movie stars, the celebrities who used to pepper the Kennedy administration in the '60s, who represented the glamor and excitement that the Kennedys have always evoked.

They seem so full of enthusiasm for their failing candidate that if you closed your eyes you could almost forget you were in New York for this list-less convention of 1980 and pretend it was the '60s again. Their black humor in the face of defeat reflects a wit and style of the Kennedy ear that has so haunted the Kennedy successors.

"Why can't I do this for a winner sometime?" remarked one of the Kennedy supporters."Maybe I'd get an embassy."

Betty Bacall was particularly vociferous in her support of Kennedy and her contempt for Carter.

"Teddy is much more Democratic than Mr. Carter," she said, "whom I personally can't abide . . . Teddy could wake everyone up again and make them believe that something terrific can happen."

"The biggest accusation against Teddy," says Adolph Green, "is that he represents the '60s. So he represents a time when there was hope and joy. I don't see anything wrong with that." Missing Oomph

The convention floor is teeming with people, all seeming without much of a purpose. Hamilton Jordan tries to walk through the floor for a little politicking and before he has gotten halfway through, he, like the Pied Piper, is being followed by over 20 reporters and cameramen and photographers and sheepishly has to disappear back into the Carter trailer.

Except for Bob Strauss, Jody Powell, and the irrepressible Miss Lillian, the carter family and staff deliberately keep themselves under wraps. l

"The family and the staff can't do anything but hurt the president now," says one inside Carter staffer.

At most conventions there are a lot of parties and this one is no exception.

But this time the families and the staffs of the two leading candidates, Carter and Kennedy, are rarely in evidence, even at the parties. Only Jordan, Powell and Charles Kirbo showed up at a Newsweek party Sunday night. At Arthur and Alexandra Schlesinger's big bash Tuesday night, the night of Kennedy's speech, there were no Kennedys in sight. The decision to lie low on the part of both contingents took away whatever excitement and energy there might have been from an already largely uneventful convention. Even at the convention hall the night Teddy spoke. Jackie Kennedy Onassis never showed up. The mere image of Jackie in the Kennedy box watching her brother-in-law give an emotional speech might have been enough to give the convention that extra ooomph the Democrats usually provide for their spectacles. The Kennedys used to function as American royalty and provide a sense of glamor and energy. That is no longer the case. Only Teddy reminded people in his moving speech Tuesday night. But by Wednesday, the speech was last night's news and Carter, the non-hero, was the man of the hour. 'The Arid Generation'

Mario Cuomo is the lieutenant governor of New York and also leads the Carter delegation. A dark-haired man with a lot enthusiasm, feistiness and energy, he is the kind of person you would expect to find supporting Teddy Kennedy. But ask him about Carter and he will wax supportive for 15 minutes, telling you of all the president's accomplishments. Then ask him about Kennedy and he goes silent. Then speaks softly. "Kennedy wasn't running when I went with Carter," he says finally. "You know the most important thing about Teddy Kennedy's speech? It was very good evidence that compassion is still available. We were beginning to get the sense that liberalism doesn't go. People want to believe in believing. They have to believe you don't have to settle for gruby reality. One of the most accurate and sad commentaries of our times was that song from 'The Graduate by Simon and Garfunkel, 'Where have you gone Joe Dimaggio. . . .' There's nobody to believe in, there are no heroes. This is an arid generation. What Teddy did was give people some great lust for something noble to believe in." Ahead of the Cycle

"I was opposed to Teddy's running," says Arthur Schesinger, dressed casually in an open-necked sports shirt and khaki pants. "I thought it was a mistake. Kennedy stands for a traditional affirmative approach. Carter in my view is not a liberal in any sense of the word. Carter has been president for four years and still has no consistent idea of what direction he wants to lead the party. I did not vote for Carter in 1976 and I will not vote for him 1980. He has been a disaster for the country and a diseaster for the world. If you don't want to change you Don't have to have a sense of direction or vision. . . . But Teddy was a couple of years ahead of the cycle. Liberalism is something a tired country doesn't like to think about.

"Liberalism is out of fashion. But it will come back into fashion. In the '50s we had this same business that liberalism was dead. Then the '60s came and carried the whole thing further. . . . You get tired. You don't want to be bothered. It's a listless period. Apathy, Everyone is tired." The Personal Touch

State Sen. Jack Brennan of Massachusetts shrugs. He is having a hard time coming up with reasons why he is a Carter delegate. "Of course it would be a lot easier supporting a guy who is flying high than one who is flying low," he says. He is still trying to come up with a reason. "Well," he says. "Well," he says finally, "the main reason I'm for Carter is that it's been 24 years since we've had a two-term president." He brightens. "And also . . . he called me personally and asked me himself." The Call to Unity

Last night, Jimmy Carter had a call for Teddy Kennedy, too. "Ted," said Carter in his opening remarks, "your party needs -- and I need -- your idealism and dedication working for us." And then toward to the end of the speech -- a rather prosaic speech to a less than enthusiastic crowd, many of whom did not applaud him and even once him -- Carter reinforced his view of the world especially in contrast to that of "Republican leaders." All of us can sympathize with the desire for easy answers. There is often a tempation to substitute idle dreams for hard reality." And finally "the choice -- the choice between the two paths to the future -- could not be more clear. If we succumb to a world of fantasy we will wake up to a nightmare. But if we start with reality and fight to make our dreams a reality -- all Americans will have a good life, a life of meaning and purpose in a nation strong and secure." The Ill-Timed Idealist

When Teddy Kennedy removed his name from nomination he said in his announcement, "I am a realist." In fact, that is exactly what he seems not to have been through much of his campaign, and it seems also what the voters and the Carter delegates have held against him. Kennedy is the idealist in a time when idealism is not fashionable Carter is the realist in a time when realism is only too evident.

In his speech nonimating Jimmy Carter to the convention, Gov. Bob Graham of Florida emphasized this by saying, "The man I will nominate practices the politics of reality in a complex world where there are no easy answers." and it was Teddy Kennedy who would speak of "yearning for a new hope," "we kept th faith," "the cause endures, the hope still lives, and the dream shall never die."

When the band struck up "Happy Days Are Here Again," both his speech and the music seemed almost in anachronism, like hearing a song shared with a lost lover that evoked all the old memories and made you cry, yet knowing you could never go back and not really wanting to. Though there were some delegates -- particularly those from the South -- who sat on their hands, grim-faced, during Kennedy's speech, most of them allowed their emotions to give way in what generally uncharacteristic for this campaign. The next day many of the Carter delegates admitted they had been moved, had savored the experience. But they were back to business as usual.

These are not the same delegates who have been at Democratic conventions in the past. They are not the old-time pols, the wheeler-dealers, the schmoozers, the sophisticates, the bleeders associated with liberal Democratic politics.

These people are youngish to middle age; many of then are delegates for the first time. They are technicians rather than politicians. They are clinical, unemotional, reasistic. Joy, hope, faith, passion, are words one does not hear at this convention. They are here to get a job done, make do, get by. There are no visions at this convention. There is no romance here. They are not a team, not a group. They are not bound together by a fervor for their candidate. They are individuals. There is not a great deal of caring. tMost of them are more excited about being included in the process than about the people the process is about. If, in Detroit, the Reagan supporters seemed to go along with anything the candidate said, these people seem more resigned than anything else. This is what we've got, let's make the best of it. And what they've got is a president who represents -- literally. If the country is in limbo, in flux, in an ambiguous phase, then Jimmy Carter is their true leader, the perfect representative for a confused constituency. Great Expectations

Libby Stout, a Carter delegates from West Virginia, doesn't even have to stop and think why she's for Jimmy Carter. "They expect him to be a cross between Babe Ruth, Plato and Jesus Christ," she says. "They expect too much of him. These are troubled times. He's a victim of the times. I identify with Carte. He's my kind of people. He's an average citizen. He came from a small town in Georgia. I'm from Appalachia. People identify with people like him. I think he's doing everything he can." One Campaign at a Time

Bill Daley is the son of the late Chicago mayor, one of Jack Kennedy's greatest supporters. Bill Daley is an Illinois Carter delegate. He is a man who understands politics as well as any young man in the country and a man who is puzzled about the new crowd of delegates.

He is sitting in the Illinois delegation on the floor of the convention hall. It is late. He is tired. A fellow delegate has just spilled Coca-Cola all over his shoes and trousers. He is trying to be patient and talk above the incessant din.

"With reforms," he says, "you end up with fewer long-term political people. I sensed a start of it four years ago. They aren't your typical political types. A lot of people think there will e more of a balance four years from now. You'll get more people who will go back and work for the candidate instead of 3,000 individuals."

As for his own deep personal commitment to Jimmy Carter. . . . "Carter? Ummmm, I think he, uh . . . " He shrugs. "These are a very tough four years. There are a lot of problems, a lot of mistakes. But there are more pluses than minuses and that's really what you get down to. I support Carter over Kennedy because on the whole Carter was the incumbent. People are worried about how we're going to win. There isn't that enthusiasm, but they like him. . . . I like him. No, I don't love him."

As to wether he will return to Illinois and work for his candidate, Bill Daley looks a little embarrassed. "My brother's running for state's attorney," he admits after a pause. "I'm running his campaign and that's all I'm going to do." Lost Exuberance

Sixty-third Street was blocked off from traffic and police ringed O'Neal's Baloon for Tip O'Neill's party. Bagpipes were playing, a huge buffet was set up and the speaker of the House and chairman of the convention was holding forth -- kissing and hugging his guests, glad-handing other politicians, wooing the press, posing for pictures, laughing and joking with anybody he was near and doing all the things that most old-time politicians would do.Only it, too, seemed somewhat of an anachronism, this strange political behavior in this antiseptic convention of 1980. Even Tip O'Neill, one of the wiliest and most sophisticated politicians in Washington (and no great fan of Jimmy Carter's) seemed a bit nonplused by the new breed of Democrats surrounding him.

O'Neill, after all, is a Boston Irish politician, an old-time liberal. Here he was in what should have been his element -- as chairman of the Democratic convention -- and nobody to play with. Oh sure, they could wheel and deal a little and negotiate about whether Carter would call Teddy personally and ask him to be on the platform with him, and he could pound the gavel and say the Ayes have it when it sure sounded like the Naws, but that's smalltime. They just weren't his people out there on that convention floor.

"There's a swing from liberal to progressive in this country that was in process," says O'Neill, his arms around several guests as he spoke, occasionally pausing to wave to a fan or smile for a photographer. "That's how Carter got the vote in the first place. The swing was on when the campaign really started. They felt Kennedy was too liberal and Kennedy when he came in to see me to say he was going to run. I said listen, you've got to remember one thing -- we appropriate $87 billion a year and at least $50 billion is at the disposal or discretion of the president or his supporters. That's politics. And there's nothing wrong with that," he says with a wink and a smile.

"But this type of people who support Carter, they aren't the exuberant type. The exuberant type is rare in politics these days. That was a rare occasion when Kennedy gave his speech the other night. You won't see anything like that again. When you come back towards the middle you lose that exuberance. That's the nature of politics."

"Who are these people supporting Carter today?" He smiles broadly, his massive hulk begins to shake as he chuckles and a lock of white hair droops over his forehead. "The Carter supporters are people who think they're with a winner." Idealism and Greatness

The little Nixon child is trying to climb the stairs up to the house and Tricia gets up to keep the baby from hurting itself. Pat Nixon, still relaxing in her chaise, smiles as her grandchild gurgles and laughs playfully.

Inside the Schlesingers' house, Arthur Schlesinger is still puffing away on his cigar. The phone has been ringing all during the interview, people thanking him for the party last night, and his wife, Alexandra, appears to say she is going out for a while.

Schlesinger is talking now about idealism versus realism. "No one was more realistic than Roosevelt," he is saying. "And Jack Kennedy used to decribe himself as an idealist without illusions. The important thing is realism in means and idealism in ends. But when you're in the doldrums you don't need idealism because nobody wants to change anything."

And once again Athur Schlesinger quotes Emerson. "Emerson," he says, "once said nothing great can be done without enthusiasm."

He gets up to walk a guest to the door.

Outside in the garden, Tricia Nixon Cox bids her mother goodbye and takes her baby up the stairs, disappearing into the townhouse. Pat Nixon waves goodbye to her daughter and grandchild, then leans back in her chaise to rest.