Slicing kielbasa and singing along to the tunes of a double-barreled euphonium, Ronald Reagan seemed to be having the time of his life.

The same could not be said for his luncheon guests left and right -- George Bush and Jack Kemp, look-alike, dress-alike, act-alike bookends of anxiety.

For Bush, the luncheon with his primary campaign conqueror, Reagan, and his vice presidential rival, Kemp, was just the first of a series of events that would carry him along a roller coaster of emotions from the peak of frustration to the depths of political depair, and finally -- just when he was certain that he was a loser once more -- to an unexpected victory.

But at noon, no one could foresee what lay ahead, not even Reagan, as he lunched while flanked by his matches set of hopefuls, Bush and Kemp.

They sat there tall and handsome, dressed in their dark blue suits and bright red ties, laughing uproariously at the jokes of their hosts and forcing smiles and small talk about everything except the only thing on their minds.

Like finalists in a bathing suit competition, they were giving it one last all to please the judging panel of one, each wanting very much to be crowned as the winner of the Ronald Reagan vice presidential pageant. Lunch at the Polish-American Club in Hamtramck adjourned with handshakes and smiles and back pats from the judge, but no verdict.

Officially, this was a luncheon for the 50 or so prominent Republicans who rode the convention circuit this week addressing the various state caucuses on the attributes of Reagan. But the fact that two of their number were finalists on Reagan's vice presidential list -- and the fact that Reagan aides had carefully assigned them seats flanking the GOP nominee for president -- added suspense to the only drama in town, the selection of Reagan's running mate.

"I don't know -- gee, I really haven't heard a thing," Bush said as he entered the hall in this heavily Polish community of auto workers. Bush and Kemp worked the room, shaking hands, but they were carefully back at their places when Reagan arrived. The polka band struck up "Happy Days Are Here Again' and then swung appropriately into "Hey, Look Me Over."

Bush, wanting to leave nothing to chance, got back to his feet in plenty of time to greet Reagan, who reportedly harbors some doubts about whether Bush is truly presidential.

The gesture was marred slightly. Bush reached across the circular table to shake hands with Sen. John G. Tower of Texas and in the process managed to get powdered sugar from a pastry plate all over his dark blue right sleeve, and then his suit jacket pocket.

So when Reagan arrived, Bush looked like a long, lean version of Inspector Clouseau, rubbing, anxiously at the white powder and trying to restore a presidential image to his suit.

But for most of the lunch, Reagan seeemed to spend his time talking with Bush. A couple of times, Kemp got up from his seat and table-hopped the room.

"It was small talk, just small talk and pleasantries," Bush said, leaving the hall.

Said Kemp, apparently striving to find parallels with his political leader:

"We talked about his days as president of the Screen Actors Guild and my days as president of the Players Association of the football league."

Reagan and his guests were serenaded throughout the luncheon by a band that featured a rotund strolling maestro in a red and white striped blazer and matching bow tie who got some help from Reagan in trying to get a sing-a-long started. Somewhere well into "You Are My Sunshine," Reagan put down his fork and burst into song, prompting Kemp to observe quickly, "Hey, he's good." Bush remained smiling but silent.

Later in the afternoon, Bush went to the convention hall to rehearse for the first time speech he would give to the convention. In a bit of dramatic planning, Bush and his top advisers decided to scrap the speech originally written for the occasion. "All the other speeches had already used our best lines," one of his advisers said.

Late in the afternoon, Bush's chief adviser at the convention, Dean Burch, who served as an adviser to candidate Barry Goldwater and President Ford, was anxiously working the telephones to determine from his political associates of campaigns past what was beginning in the efforts to persuade Gerald Ford to accept a position as Reagan's running mate. To the Bush advisers, it seemed perhaps the only thing that would keep Bush from being offered the vice presidency.

"We really don't have anything hard on what's going on," a senior Bush adviser said as the sun was setting. "We really don't know."

But Bush was absent from his 19th-floor suite at the Pontchartrain Hotel at the time. He went to the Detroit Plaza Hotel to jog on an indoor track to relieve the tension.

EPILOGUE: George Bush carefully folded himself into the back seat of his sedan early in the night, his face flushed, his lips set tight, looking the way a man looks when he has just taken a sneak punch to the heart. Which as he saw it, was just about what had happened.

In his hotel suite, getting ready to go to the convention, to deliver one of the biggest speeches of his life, Bush had turned on the television in time to catch his former boss and longtime friend, Gerald Ford, telling Walter Cronkite and the rest of America that there had been these secret meetings with Ronald Reagan and that if his conditions were met he would be willing to be Reagan's vice president.

Bush, who had been the convention's consensus front-runner for the job, grabbed his speech text and went down to the car for the ride that he had long awaited but now no longer wanted to make.

At the convention hall, he gave his speech, listened to a loud demonstration in his support, then returned to his hotel suite, for what he figured would be an evening of solitude but not solace.

More than an hour later the Ford deal fell through, and as Bush later explained:

"Just a few minutes before he appeared at the convention -- out of the clear blue sky I might add -- Governor Reagan called me up and asked if I would be willing to run with him on this ticket. He was most gracious in the invitation . . . I was surprised . . . I feel honored."