The earnest-looking man from North Dakota sidled up to the mayor of New York City.

"May I bother you for your autograph?" the young man asked over the din at the Washington Hilton.

"That'll be a dollar," replied Edward I. Koeh.

New York City has had plenty of fiscal problem lately, but none so bad that its mayor really wants cash for his scrawl.Koch signed the man's program with flourish. No charge, he said.

These days, New York apparently can afford more than free autographs. Specifically, New York and its industries can afford festivals for Congress that cost $170,000.

Like the one at the Hilton last night. There were bands, there were models with dresses slit to their thighs, and there was food -- from won-tons to bagels to four-foot subs. There were also 1,000 invitations, including 30 senators and 250 representatives.

Koch, who was talking at the same time he was fork-wrestling with one of hundreds of oysters spread every-where, insisted that the party was just your standard thank-you affair. A wooing of Washington? Never.

But Rep. John Wydler (R-N.Y.), for one, disagreed. "You wine 'em, you dine 'em and you soften 'em up," he said.

And New York Gov. Hugh Carey, for another: "I don't know any better way to eliminate friction than with lubrication," he said.

The official reason for the party was to thank Congress for sending $1.65 billion to New York City last year, thereby bailing it out of impending bankruptcy. And Congress, although it sent the money more or less begrudgingly after a hot summer fight in 1978, seemed delighted that a city not known for courtesy had the courtesy to remember its friends.

"Do I like New York?" asked House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.). "I think New York is the greatest city in the world I think there are three great cities in the world -- New York, Boston and Rome."

At which point the nation's capital wass brought up. "Washington?" O'Neill pondered. "Ah, umm, err . . . " He ended the sentence in a rumble under his breath.

Besides O'Neill, the festival attracted lots of other political celebrities. Sen. Ted Kennedy (D-Mass.) made his usual quick-in-quick-out appearance, but wasn't besieged by the usual herd of reporters asking him when he's going to announce for president.

"This is calm," observed Carey, who was standing near the small, relaxed pack around Kennedy. "New Yorkers take these things in stride. We're not so celebrity-conscious."

Also on hand were the two senators from New York. Jacob Javits talked about SALT and Daniel Patrick Moynihan talked about cheese. Or cheese and Gov. Carey, to be exact.

"Hugh and I were arguing last year about Philadelphia Cream Cheese," Moynihan said. Carey said it came from Philadelphia, N.Y.; Moynihan said it didn't. Moynihan won. "It comes from South Edmonston, N.Y.," he said. "You didn't expect me to tell you about an argument that I lost, did you?"

The food, Carey swore, was all from New York. It certainly looked and smelled that way because a walk past the endless buffet tables revealed not the uysual pate and meatballs but pork, steak, salami, stuffed cabbage, rice, pasta and cheesecake. It could have been a mini-tour of Chinatown, Little Italy and the Lower East Side.

"We cleaned out tow of our counties to do this," Carey said. "Two of our counties aren't eating tonight."

Soon after that, Carey was ushered into a small room for pictures with Koch and other New York representatives.

"You can't put your hands in my pockets because they're stitched shut," Carey warned Koch.

"Hugh," Koch asked, "would you do that little dance number you were practicing?"

And that was just one of many exchanges the occurred last night between politicians who usually call each other "Congresman" or "Sir" during public working hours.

Mideast negotiator Robert Straus, for instance, told Joanne Kemp, the wife of the Republican representative from New York, "Anyone who looks as good as you can do better than that." Strauss gestured at Jack Kemp, her husband.

Replied the representative : "But I've got a lot of money. A lot of money."

There were also those who thought the party was just plain extravagant. "I'm a little amazed," said Rep. Toby Moffett (D-Conn.) "But I'm sure Ed Koch has a reason for it."

And when it was suggested to Rep. Joseph Addabbo (D-N.Y.) that $170,000 might have been spent on poor people rather than oysters, he countered:

"Well, we hope that the friends we make here will bring aid to all the people."

The after-dinner entertainment was, appropriately, New York. Kity Carlisle and Tony Randall were co-hosts of a show that included music from "West Side Story" and "New York, New York." Two performers from the New York City Ballet danced to George Gershwin's "The Man I Love."

But New York stays up late, and Washington goes to bed early. With an hour still to go untill midnight, a time when things are just warming up in Manhattan, Washingtonians headed out into the cold for the limos and taxis to take them home.