More than 800 people, some of them wearing skimpy costumes with white bunny tails attached, crammed into the National Press Club ballroom last night, capping a day of attention devoted to Hugh Hefner, whose "dream" 25 years ago of starting a popular "entertainment" magazine has turned into a quarter-billion-dollar empire.

Hugh Hefner is the man who made the phrase "cheesecake photo" an anachronism. Hugh Hefner is the man who built an empire with $6,000 and the contents of a brassiere. His power is such that high-level White House employes, hundreds of reporters, the mayor of Washington, and celebrities about town will turn out in his honor to drink lukewarm champagne, get their toes stepped on and ogle a number of scantily clad young ladies.

Hefner, and his daughter Christie, and his associate publisher, and the president of Playboy Enterprises, and Hefner's girlfriend -- whom he calls BabyBlue -- held court in Washington all day yesterday, commemorating the 25th anniversary of Playboy magazine. With a frosting of political celebrities (Sen. Charles Percy, Rep. Abner Mikva), and a veneer of social largesse (announcing the gift of historical press papers to the Chicago Public Library) to add a sense of purpose, Hefner et al were treated yesterday like visiting royalty.

Playboy is spending about $1.5 million celebrating its 25 years of existence, according to a public relations man. There already have been parties galore in Chicago and Los Angeles, New York tomorrow, and a superduper 25th-anniversary edition of the magazine that cost a record $3.

"I was really worried about charging that much," said associate publisher Nat Lehrman. "But it sold like crazy."

Miss 25th Anniversary Playmate herself, Candy Loving, was at the party, holding court in a white jersey dress. Candy Loving took a leave from studying public relations at the University of Oklahoma to spend this year doing promotion for Playboy, because she "believes in it."

"There's a stigma attached to the Playmates," she said. "Everyone thinks they're not too bright and are only interested in taking their clothes off. My job is to show that we can talk! We're sensitive! We're just regular people."

"How did you feel about your photographs? I don't think your intelligence really came across," said an earnest man from Aviation Week to her. She said she liked her photographs, and in fact thought that all the photographs in Playboy are tasteful.

Asked about some of the explicit and acrobatic shots she said:

"Well, they offend me, too. But you don't have to look at them."

"There's no question about it, Playboy vastly improved my adolescence," said presidential assistant Greg Schneiders, interviewed near the champagne table as people elbowed around one another.

Mayor Marion Barry, accompanied by his wife Effi, arrived late and was promptly dragged off to have his picture taken with Hefner before he left for New York. Barry admitted that he has read Playboy, and was approving of the idea that a Playboy Club might be started in Washington, because it would be good for the city's economic development. "But that is not the most pressing problem on my mind," he said. "The Sexual Revolution, that is."

Sen. Percy, who along with Rep. Mikva was a host of last night's event, said he has "always sponsored any Illinois industry that wants to be here in Washington." Yes, he said, some of his constituents might be unhappy that he was lending his name to this kind of magazine but he noted that several years ago when he was interviewed for a story in Playboy he got a lot of favorable mail from clergymen.

"Where were all of you when International Harvester was in town?" he asked the crowd, many of whom worked in the press building and found it handy to come up for a free, after-work drink or two.

"This is clearly a Washington party, not a Playboy party," said a man who has been to both. "For one thing, the food at a real Playboy party is always fantastic. And it's a more homey atmosphere. Here you have a lot of second assistants and aides and reporters who are here because they're curious."

Earlier Hefner submitted to what was billed as "the traditional no-holds-barred" press conference-lunch at the National Press Club, where he fielded such questions as, "Why isn't there a Playboy Club in Washington," and "What to you do in your spare time?"

"Rumor has it that those stars by the 'P' (of Playboy) represent the number of times I have made love to the Playmate of the Month," Hefner said in response to another question. "I'd like to confirm that..." (the crowd of 300 laughed uproariously), "but I'm afraid I can't." The stars, he said, merely indicate the regional advertising editions of the magazine.

Seated on the dais with Hefner were an array of Washington media heavies and not-so-heavies. Columnist Jack Anderson, an occasional Playboy contributor, was one, as was Ted Parks, editor of the Smithsonian magazine, and Charles Peters, editor of Washington Monthly, and John E. Reinhardt, head of the International Communication Agency -- the information arm of the U.S. government overseas.

"Mr. Hefner is part of the contemporary American scene," said Reinhardt. "So is his magazine. Those who are interested in contemporary America would be interested in his views, whether or not they subscribe to them."

Present at all events was Hefner's daughter, Christie, at 26 the vice president for public relations for Playboy Enterprises. A poised, discreetly dressed young woman without the glossy make-up characteristic of the Playmate or Bunny, Christie was the focus of considerable curiosity.

"That couldn't be Hugh Hefner's daughter," said Marty Kaplan, special assistant to Vice President Walter E. Mondale. "She hasn't been airbrushed."

Although four years older than Hefner's current flame, BabyBlue, Christie seems accustomed to that aspect of the Playboy Philosophy. "The kinds of relationships he has are the only ones I've ever been aware of," she explained. "After all, my mother lives with a man who's 12 years younger than she is."

A Phi Beta Kappa graduate of Brandeis University, Christie answered repeatedly the same inevitable question, each time making her response sound as though she'd just that minute thought it up. And what is it like to be Hugh Hefner's daughter?

"Oh, he's wonderful," she would say. "But you have to understand that I didn't grow up living with him and I didn't take his last name until I was a junior in college. So by the time people found out Hef was my father they already knew me. In most people's minds I just appeared out of nowhere. Sometimes I feel like Minerva who sprung full blown from Zeus' head.

You know, where did hihs girl come from? We didn't even know Hef had kids..."

Meanwhile, BabyBlue -- whose name is really Sondra Theodor -- drifted around in champagne-colored harem pants and a cream-colored blouse. She is a former Miss July. Around her neck she wore a necklace with BabyBlue spelled out in diamonds.

"It's because it was the first song we danced to the first night we met," she said. "So he calls me BabyBlue."

Hefner, 52, said that Playboy's plans for the next 25 years are to keep expanding, all over the country and the world. More clubs, casinos, and even a new magazine ("Games") and a new game (Playboy). Hef likes games, he said. That's one of the things he does in his spare time.

But a major part of the Playboy Philosophy is to Have Fun. Forget the Puritan work ethic, that anti-sex, repressive, oppressive mental and emotional girdle. Be Hugh Hefner and lead "the ideal bachelor existence," as he put it.

"You know, the magazine is not the most important thing in my life," he said. "Romance is the most important thing in my life."