The Bullets had just beaten Atlanta in the seventh game of their highly intense playoff series and Frank Render was beside himself with joy.

So he stepped outside his Alexandria residence and yelled. Not that loudly, but he did yell. And it made him happy.

"I just couldn't contain myself anymore," said Render, a fried of Bullet star Bobby Dandridge and an executive for a local corporation. "And my neighbors had the same feeling. They came out and we yelled and chatted. It wasn't anything outrageous but there was a feeling of togetherness.

"I think we all just wanted to be a part of what the Bullets did. They've brought something to this town and everyone is starting to recognize it."

It's called Bullet Mania and this year the fans aren't waiting until late in the playoffs, as they did last season, to jump on the bandwagon.

The Bullets didn't have a sellout in the playoffs last year until the conference finals against Philadelphia. Their last three playoff games this season against Atlanta filled Capital Centre and team officials expect the ensuing postseason home contests to draw capacity crowds.

Talks with souvenir salesmen and local bartenders reflect the growing interest. People are gobbling up the revised Fat Lady T-shirts (The Fat Lady Will Sing Again) and the Bullets dominate cocktail-hour conversation sin pubs.

And now, with President Carter making an unexpected appearance at the Centre, the House the Abe Pollin built sudenly is an "in" spot for celebrities. Politicians and society types are clamoring for tickets, a la the Redskins, much to the delight of Bullet officials.

"We used to have an assistant call us for tickets and they'd give them to friends," said Chip Reed, the Bullets' marketing manager. "But now the man himself is calling, a senator or a representative, and he's saying, 'Hey, I need a ticket and it's for me. I want to see this team play!"

Reed still is talking about the huge box-office turnout (6,000 tickets sold in three hours) after the sixth-game loss to the Hawks. Bullet fans always lined up for tickets in the past after series wins, but this was unprecedented-they wanted to support the team in its hour or need.

Even the demeanor of the Centre crowds have changed. The noise level normally has been high for playoffs, although the regular-season crowds are among the quieter in the league. But for the seventh game against the Hawks last Sunday, the Bullet partisans scaled new heights in ear-splitting sound.

From the moment the players made their initial appearance on the court through the three-minute standing ovation preceding the introduction of the starters until the final seconds ticked off the clock, the Centre rocked as it never has rocked before. The inhibitions of former years disappeared, to be replaced by some passionate rooring.

"Maybe," said Reed, who had wondered where the fans had gone during low-attendence nights earlier this season, "we have finally arrived. I hope so."

Doug Hinds had season tickets to Bullet games before he was transferred to California. He once was wired by medical technicians to measure his pulse rate during games; that's how emotionally he followed the team.

He made it through the regular season with hardly a rooting scar but the playoffs were too much for him to take. He flew into town last Sunday, figuring he could watch three playoff games in a week before he had to return home. When the Bullets beat the Hawks, his gamble paid off.

Leonard Downie, former metropolitan editor of the Post now is the paper's bureau chief in London. A season-ticket holder, he was an enthusiastic fan who objected vehemently to in consistent officiating. Calm by nature, he was a different person when watching the Bullets. He was not calm.

An hour after Sunday's triumph, Downie was on the phone from London, asking for the final score. It was 1 a.m. London time.

John Schreiber could get tickets to Bullet games-frieds have season seats-but he can't bear to watch contests on television this time of the year, much less in person.

So he lets his wife view them on the tube and, if the outcome is right (a Bullet win), she can announce the result. If it isn't, well, she has to break the news very carefully.

"I know it's foolish," he said, "but they get to me. God, are these games exciting? But one of these days, I will sit there and watch it. I really will."

Schreiber is among many fans who cannot watch their favorite team play its games, too much pressure.

Joe Haardt had long fingernails two weeks ago. "I made it point to grow them," he said, proudly.

Now those nails are gone. It's playoff time again.

"You might say I root with enthusiasm," he said. "I moved to Fort Lauderdale but I couldn't stand being away from the Bullets. That's one reason I moved back."

Haardt is the No. 1 Bullet fan. No one else has had a season ticket longer-16 years-nor has anyone, he believes, rooted for the team for such a long time, including its owner.

"I started pulling for them when they were in Chicago," he said, "and I was going to Notre Dame. I had season tickets when they were in Baltimore and I kept them when they moved here."

Haardt, who used to live in Loudoun County, would make the 1 1/2 hour trek to Baltimore every game night to see his beloved Bullets. The journey is shorter now and his spirit has changed.

"When they used to get knocked out of the playoffs, you couldn't talk to me for weeks," he said. "It's not that bad anymore, maybe just a few days now."

Haardt had his choice of seats in the Centre. He picked one just behind the Bullet bench in the first row. "I can get involved there better," he said."I like the angle."

When he thinks games are really important, he breaks out his secret weapon: a lucky Bullet T-shirt purchased when the team was in Baltimore more. The T-shirths record: 16-2.

Last year, Haardt was scheduled to fly to Seattle for Game 7 of the championship series. But his father died the night before.

"When the Bullets got back into town," he said, "(Centre President) Jerry Sachs called me and asked me if I wanted to come out and see the trophy.

"It was a tremendous gesture. I went out there and I cried. I cried for the trophy and I cried for my dad."

Annie Lesner isn't competitive by nature. "I could care less if I win or lose in anyting," she said. But when it comes to the Bullets, her personality changes.

"I have butterflies the day of games," she said. "I don't think the players get as nervous as I do. At least they can work it off. I have to sit there and suffer.

"I feel for them. I identify with them. It's terrible. We regulars knwo when they get haircuts-we talk about it-and we worry about Mitch Kupchak's back and Lary Wright's lack of playing time, things like that."

Lesher became a season-ticket holder in the early 1970s. She never had liked basketball that much, but after seeing one game, she was hooked. "It was also the first time I had ever rooted for a winner," she said. "Growing up in this town, I had rooted for the Redskins and Senators. The Bullets were different."

Her love for the club also got her a job. Sen. William Proxmire had the seats next to hers at the Centre and they talked during games. She finally asked him for a job and he agreed. She now works for Sen. Paul Pryor.

"I went to Seattle last year for the seventh game," she said. "I was happy when they won, but I felt more relief than anything else.

"Ever since 1975,when we lost to Golden State, Ihve changed. I don't get quite as emotional or as noisy during games. I think I'm calmer; 1975 was such a letdown."

And how does she feel about the bandwagon fans?

"It's about time they realized what kind of team we have," she said. "I think if we win one more championship, it will really put the Bullets over the top.

"But you can tell the new fans aren't really sophisticated. They make noise at the wrong time and they don't appreciate the finer points, at least not like the regulars appreciate them."

Jack Scloffs sits at midcourt, about three rows from the floor. No one makes more noise at a Bullet game than Jack Scloff. He has a hoarse voice and the notoriety to prove it.

Scloff is a specialist. He concentrates on the refs. He has yelled at them so long almost everyone of them knows him by now. They chat with him, smile at him and, he believes, listen to him.

At least until the Merchant of Venom came along.

"He's cut into my influence," said Scloff, a travel agent. "He yells so many vicious things at the refs that it's killing me. They don't want ti listen to anyone anymore.

"I know I used to have an edge with some of the refs. I could get calls in games from them. They'd kibitz with me but they'd also listen to me. But the Merchant has ruined that."

So Scloff has taken on a new role.He now is a fan-in-the-stands Bullette, a street-clothes cheerleader who stands, waves his arms and urges the crowd to rise with him and really behind their team.

"I feel it's my responsibility," he said. "Abe and them come up to me and ask me to help out. These new fans, they sometimes forget to cheer. It never hurts to lead the way for them.

"But I've changed now. Like the song syas, 'Is that all there is?' Whether they win or lose, tomorrow still comes. But tomorrow is nicer if they win."

Of all the Bullets' longtime season ticket holders, Alan Marks may be the most introspective.He is fascinated by the nuances of the game, marveling at feats he never could duplicate as a "poor, frustrated player."

Marks once had not missed a Bullet home game in five years before being sidelined by a back injury. But his basketball emotions have changed as he has grown older.

"Maybe it's because I've turned 40," said Marks, a stockbroker. "I don't go to away playoff games like I once did. And I'm bothered by the commercialization at our home games.

"Why do we need commercials on the TelScreen? And why do we need the TelScreen to tell us to stand up and give the players a long ovation. So much of the enthusiasm is manufactured now. I wish it was spontaneous. Even that Fat Lady was awful."

The Fat Lady hasn't been around for weeks. The symbol of last year's championship triumph, she paraded around the Centre during games, waving a sword and yelling.

"We are holding her in semiretirement," said Reed, trying to keep a straight face. 'She is our secret weapon. When we get into the championship series this year, she will return."

"But," Reed added, laughing, "she may not be able to find a ticket."