If you were going to a party where you would meet Cary Grant, see most of your close friends, eat lobster until midnight, wear a low-cut black dress, be accompanied by your husband in a tuxedo and serenaded by Peter Duchin himself and his orchestra, you too might spend $140 to have your hair cornrowed. Like Bonnie Slotkin did for the American Cancer Society Ball at the Washington Hilton International Ballroom Saturday night.

Cary Grant gazed up at Bonnie Sltokin's daugling Bo Derek style braids and asked how long it took (seven and a half hours).

"I think she looks exqusite, and it was well worth my money," said her grinning husband, Jay Slotkin, a periodonist, to giggles from friends. "But I want it out by Wednesday."

This ball for them -- and many of the others among the 1,462 people who bought $150 tickets -- is one of the social events of the year.

It is for a good cause -- it will raise close to $200,000, more than any other single event that the American Cancer Society sponsors anywhere in the country.

It is fun -- no one discusses the crises of the world.

It is sumptuous -- long buffet tables, a ballroom decorated in circus motif with pink and red carnival decorations, elephant statues, stuffed monkeys. "We hors d'oeuvers all night." said Howard Baylin, who each year designs and provides the decor for free," and we breakfast at midnight."

And there is a star -- this year, Cary Grant, "honored guest," widely thought at Saturday's ball to be one of the nicest stars the ball had had -- even nicer than Elizabeth Taylor, a previous ball star, one guest suggested.

Contributing to the circus motif, literally hundreds of guests waited in line at one entrance of the ballroom to shake Cary Grant's hand, have a picture taken, whisper in his ear.

(in al fairness, it must be said that some of these people didn't realize there was another entrance into the ballroom.)

"I told him my husband was suing him for alienation of affection," breathed Ruth Chernikoff. "He said, "'Oh, your husband wouldn't dare do that.'"

Grant good-naturedly shook hands for about two hours, taking breaks for sips of wine and handfuls of popcorn, provided by one of the popcorn "vendors." sNext to him stood his guest -- Barbara Harris, a 29-year-old Jacqueline Bisset look-alike, who works in public relations. She provoked admiring glances from male guests and some polite discussion of just who she was. Friend or girlfriend?

"Friend, girlfriend," said Cary Grant, shrugging. "She's one of my close friends."

"Why would I be tired?" Grant asked at the end of the two-hour marathon handshaking session. "What have I done? Want some popcorn?"

He also put up with questions about his favorite movies -- "They're all my favorites" -- and commentsd about how much is "Philadelphia Story" was enjoyed.

"My 'Philadelphia Story?'" he asked. "Haven't they made two or three since then? That was done by a playwright named Philip Barry. He did all great plays. In each of them he had one point -- making fun of the rich."

Asked if he missed making movies, he said. "Absolutely not."

"He doesn't look like he used to," noted Lynn Rosenberger to her date, Navy ensign Tom Harper.

"Hey," said Harper, a handsome 26, "when I'm 76 I hope I look like that."