The biggest surprise at Dan Quayle's surprise birthday party last night didn't pop out of a cake. He popped out of campaigns past.

It was the vice president's old friend Lee Atwater, fighting an inoperable brain tumor but still sounding every bit The Chairman.

"I think he's doing good. He's speaking better, looking better, he's looking more mature," said Atwater of the 44-year-old birthday boy, honoree at the grass-roots gathering of 400 bipartisan fans at the Capitol Hill Club. "I talk to him two or three times a week," Atwater said, but as for what advice the former Republican National Committee chairman gives Quayle, "I can't talk about secrets."

For Quayle, as astonished to see Atwater as he was the hundreds of new friends, it was an occasion to be "overwhelmed and overjoyed. ... The big 44, you're starting to get to the age where you'd just as soon forget 'em."

"Aw, c'mon," said some of them.

Quayle's new friends, members of an informal club they are calling Friends of Dan Quayle, assured him there are more where they came from.

Stockbroker John Piper, newly elected president of the group, said so many people wanted to be at the party that 200 had to be turned away because of space limitations.

"We think this party is going to lend us a lot of credibility. We want a grass-roots group we can call upon when we see something in the media we disagree with or find unfair. And we're going to pepper the papers with letters to the editor," Piper said.

Looking on with the smug satisfaction of a conspiracy gone right were Marilyn Quayle and Sens. Alan Simpson (R-Wyo.) and Alan Dixon (D-Ill.), who had lured the vice president to the party on the pretext of a fund-raiser for Simpson.

"It really startled him that anyone could be that greedy," said Simpson, adding that as a matter of fact, he has no campaign debt.

"I'll always come for Alan Simpson," Quayle responded. "I'll even come for Alan Dixon too," though "one thing that I don't like about Alan Dixon is that too many Republicans vote for him."

If Quayle gave a slightly partisan cast to the evening, the club's founders said they would not.

Albert W. Angulo, a Treasury Department official, described the group as people interested in "getting the vice president a fair presentation to the public by the media. The press has been very good about telling us little about the vice president; it has not gone out of its way to tell us about his accomplishments. When we see an unfair treatment, we tell our members. They can write or not, as individuals. As a group we do nothing."

Founder Daniel Rodriquez, with the Education Department, said he got the idea for the club from a story he read about a similar group in Peoria, Ill. "They called theirs 'Hit the Trail With Quayle' but, you know, this is Washington. We didn't want to call ours that."

"These are people, just folks, for you and Marilyn," Simpson told Quayle.

Emily White, an economist at the Federal Aviation Administration, called Quayle "down-home" and "Midwestern." "I think he accurately expresses the views of most Americans."

Attorney Patricia Kuhlman said, "I think he's the average American."

"He's somebody very special. He's very intelligent," said Sunny Wong of Chester, Md. "He's nice-looking" (giggle). "And young" (another giggle).

Atwater, dressed casually and wearing a baseball cap to cover the scar from his most recent surgery a couple weeks ago, was wheeled in to wait near the door for Quayle to arrive. The vice president had a big hug for him, and Marilyn, who visited him when he was hospitalized in New York, called out an affectionate "oh, Leesey," when she saw him.

Quayle's "just as nice" as his boss, George Bush, Atwater said. "You know, that guy calls me every week. The day that {Soviet President Mikhail} Gorbachev left town, I heard the helicopters flying off. The minute {Bush} got done, he called me and said, 'I've been thinking about you all week. I was just too busy to call.' "

Atwater called Bush "underestimated; the most underestimated man in the White House in years. Voters are always looking for two things: honesty and decency. George Bush is above all an honest, decent man. He's a good Christian. He doesn't wear it on his sleeve, he doesn't try to flaunt it... .

"I used to like George Bush but now I love the guy."

Of both Bush and Quayle, Atwater said, "We're at a time now where there's so much baloney, any guy who's down to earth, who's organic and straightforward, is going to do well."

As for himself during these difficult months, "I had no idea how many friends I had."