"It's more like a bar mitzvah than a diplomatic reception," said one seasoned observer of the Washington party scene, looking over the room at the Georgetown Inn where a reception was being held for Henry L. Kimelman, Virgin Islands businessman and Democratic fund-raiser, who was sworn in yesterday afternoon as U.S. ambasador to Haiti.

In fact, the scene had the family-and-friends atmosphere of a private occasion rather than the more formal atmosphere usually found at embassies. Several children were running about the room, and virtually all the guests were old friends rather than potentially valuable contacts for the new ambassador -- although, of course many (including senators, business leaders and just plain influential people) were both.

There was no chopped chicken liver to support the bar mitzvah comparison, but the buffet was flanked by a sumptuous spread of smoked salmon at one end of the room and large, circular matzohs (looking like very thin pizzas with no topping) among the cheese and grapes at the other. "It's very Reform to have round matzohs -- almost Ethical Culture," said Frank Mankiewicz, president of National Public Radio, who was associated with Kimelman in the 1972 McGovern campaign, for which Kimelman was the head of fund-raising.

"I want you to meet my grandson," said Kemelman to a guest, pointing to a redheated toddler in blue overalls who was running around the room and ocasionally stumbling. Host Meyer "Mike" Feldman, proprietor of the Georgetown Inn and a longtime friend of Kimelman, was equally busy with family affairs. "I want you to meet my fiancee, Adrienne Arsht," he told one guest after another, glowing with obvious pride. "We're being married on the 28th." He pointed with almost equal pride to the hotel, saying, "This is my hotel," observing that he is spending $1.5 million to renovate the first floor and confessing, "I'm telling people I bought it so I could give a party here for Henry."

Among the friends, Marshall Miller, who lives next door to Kimelman in St. Thomas when he isn't commuting between his businesses in New York and Pittsburgh, admitted ruefully that he plays a lot of tennis with the new ambassador. "I can't avoid it, but I would if I could," he said. "If he's your partner, he's always berating you, and if he's your opponent, he's killing you.

White House staffer Mary Hoyt may have been referring to the same basic character traits, but her tone was more positive when she gave him a farewell hug and a sort of White House blessing: "If anybody knows the territory, you do, and if anybody knows how to get things done, you do."

Sargent Shriver, asked to give an evaluation of the new ambassador, hesitated a moment: "The only quotes I give are those that are handed to me by Frank Mankiewicz." But he added that Kimelman "knows the area and its problems. He has the understanding and compassion to become the best spokesman for the people of Haiti we have ever had in this position."

Kimelman, obviously happy beyond diplomatic niceties, was simply enjoying the occasion. "I feel that this is one of the greatest days of my life," he said. "I feel like I am 21 years old and no less than 12 feet tall."