It was a warm summer's night, and the young couple who had come to visit my wife and me were sitting on the sofa looking at a book that had some 19th-century photographs of Washington in it. They had just come from renting the apartment they would move into when they got married, one near the center of Washington. The girl has insisted on this: It had to be close in.

They were studying a photograph taken at Thomas Circle in 1879, where Thomas Edison had been demonstrating his new invention, the electric light bulb.

"Gee, a whole century ago," the young man said. "I don't even know who was president then."

"Rutherford B. Hayes," I said.

"What was he like?"

"A good man," I said. "He'd had a military career, then been governor. He wasn't the strongest man in his party, but got the nomination anyway because the other fellow was tainted by scandal. And the country had had enough of that. So he came into office following an era of presidential corruption that had grown up after a presidential assassination.

It was being called a time of national malaise, and he wanted to help cure all that. His wife was a beauty and he himself had fine eyes and would look right at you. The corrupt predecessor had been shifty-eyed."

"You mean Hayes was like Carter."

"Search me," I said. I didn't know. As I recalled, Hayes had come into office by taking a different stand on race from what was expected of a man from his region, had reformed the civil service and let a lot of orientals into the country whom others had wanted to exclude. But historians, in assessing his presidency, always talked, not of what he had done, but of his inability to take charge.

"If he was like Carter," the bride-to-be said, "Washingtonians must have had something mean to say about him."

"They said he stirred his lemonade with his thumb."

That didn't interest my friends very much and soon they were looking at the 19th-century photographs again: Hayes in pow-wow with Indian chiefs; Hayes and his wife reenacting the wedding ceremony on their 25th anniversary; Hayes and his treasury secretary on one of the long, lazy Sunday-afternoon buggy rides they took around this town a hundred dusty summers ago.

But there had been a lot in the lemonade remark, because it meant, for one thing, that Hayes was a man of unsettling contraditions - pious enough to be a teetotaller, and gross enough not to cater to the genteel sensibilities of this town. And it stood for the other contraditions, for he was idealistic enough to feel himself soiled by politics, but itching with ambition anyway; was tight and austere when speaking officially, and at other times sloppy and loose - lounging around the White House in shirtsleeves, work trousers and his old army service boots. On one day, he delivered a lecture on his uncompromising stand against booze; on the next, he gave in when the Russians, here to negotiate a trade agreement, demanded that booze be fetched. Then he gave a lecture on the virtues of being practical. He was so evangelical, about so many contradictory things, that he gave the impression of being a vacillating man.

Now my friends were looking at a photo of Mrs. Hayes, who'd had wonderful high cheekbones and beautiful eyes and had still been able to fit into her wedding dress on her 25th anniversary.

"Why did they call her Lemonade Lucy?" the young woman asked.

"They said she was the one who got him to take the temperance stand. In fact, they said she ran him."

Did she?"

"No. But he was unsure enough of himself to issue a denial. He was afraid people wouldn't respect hims."

That was another thing the lemonade remark had meant; that he was weak and wife-ridden. And the third thing it had meant was that the disapproval of others might be driving him mad. And Congress, too, had contempt for him - although less for this than for refusing to stroke the fur of its leaders. And so, sick of Congress and of Washington, he'd traveled around the country to try to recapture the support of the people who'd elected him, and had succeeded only in being stuck with the name, "Roving Rutherford." Americans had wanted purity in government, and he had given it to them, but now they wanted something else. When the end of his term came, he was glad to leave.

I walked with the young engaged couple out toward their car, and it was the old, warm, friendly Washington night with the aroma of honeysuckle, and crickets throbbing and most of the politicians gone home. Out there on the lawn it could just as well have been a hundred years ago, or a thousand, except for the gigantic dome of electric light over the city, that the stars were trying to poke through.

"Maybe times don't change," the young man said.

Suddenly the girl spoke up. "We had better hope that thumb goes to no worse place than lemonade," she said. Then she started talking about the H-bomb; how a big one dropped on their new apartment would leave a crater two miles deed and 25 miles out to the rim. "Frankly," she said "under those circumstances, I don't see what there is to learn from 1879."

"If you think about things like that," the young man said, "for God's sake why live in town?"

"Instant death," she said. "That's the value of Washington. I'm a nurse. I ought to know."

When I got back inside, my wife asked me what our friends had been talking about.

"What lovers always talk about," I said.

"You told us how Hayes was like Carter. But how was he different?"

"He had a beard."

"There must be something else."

"I'll try and think of something."

"I think this town ought to go easier on the president, don't you?"

"Yes," I said. "That might be a good idea." CAPTION: Picture, Underwood & Underwood