The television booth in the Capital Centre parking lot yesterday afternoon. Producer Marty Pasetta, in charge of directing the eleborate inaugural gala, sat in a state of controlled frenzy. The "Pasetta truck," as the three hastily hammered-together trailers were known, was filled with people focused on small television screens watching the performers for last night's big entertainment go through their paces.

Pasetta shouted directions: "Four go! Seven go! President! Vice president! President! Vice president! Take Five!" President-elect Reagan and Vice president-elect Bush were represented by empty wing chairs on opposite platforms, specially built and somewhat regal in apprearance.

"What the ---- is Dean doing up there?" screamed Pasetta as Dean Martin suddenly ambled on stage in the middle of singer Charley Pride's rehearsal. Martin, who appeared to be somewhat excessively relaxed, held a glass of brown liquid in one hand and was ordered offstage by a smiling Sinatra. Martin stumbled a few times a few times as he returned to this chair. "Oh, geez," muttered one assistant producer.

After Martin rehearsed his own song, emcee Johnny Carson joked, "Do you realize Debby Boone could get a contract high from this microphone?" "Dean Martin did not appear in the evening's show.

Carson remained cool throughouot, occasionally making a joke and adding "blah blah blah" to indicate that there would be more talk during the real show. "Did you know the ticket coordinator [for inaugural events] is the former valve operator at Three Mile Island?" he said at one point. Introducing Bob Hope, he said, "And here's a man who's entertained many presidents, Abraham Lincoln, Millard Fillmore . . ."

"Franklin Pierce," Sinatra chimed in.

"This is really a command performance," said Hope. "It was either this or play two weeks in Atlantic City."

The entertainers, producers and technicians putting together last night's entertainment at the Capital Centre got their respective acts slowly but surely together yesterday. The afternoon rehearsal was partly frenetic and partly professional.

The gala was to be broadcast two hours after the live performance began last night before a crowd of about 19,000 VIPs. Tickets for the sought-after event ranged from $50 to $150 with 10-person boxes going for $10,000.

Before a small audience of inaugural volunteers, the stars rehearsed some of the songs, dances and jokes they were later to perform in costume. In one row sat a few of the Osmonds, the singing family from Utah whose various business enterprises would make Ted Turner gasp. Merill Osmond, who helped produce Saturday night's opening ceremonies, was there with brother Alan largely to help siblings Donny and Marie, who were performing in the gala. All four Osmonds sat eating fresh fruit and raisins. pNo, they said, they did not think all the stars and show biz were too much for the inauguration of a president.

"People love it," said Alan.

"Politics is show biz," said Merrill.

"It's putting good ol' America back into people's hearts," said Alan. "People leave with a spark of encouragement."

"Yeah, so they spent more money than Carter," said Merrill. "But I believe people need it. They need to be reassured. With all the problems going on today, people need a little encouragement. A little show biz."

"Will you watch my coat?" asked brother Donny as he prepared to do his turn at rehearsal. He and Alan discussed whether to use new lyrics for one of the songs in which they were planning to change to "Go Ronnie Go" from the traditional "Go Johnny Go." Alan advised against it, but Donny ended up using them anyway.

"Who's that?" Merrill said, as Ethel Merman walked on stage. The grande dame of the American musical stage proceeded calmly and regally to the microphone and belted out "Everything's Coming Up Roses," the theme song of this extravaganza.

"They want us to stay and dress here," Merman said later as she sipped a cup of coffee. "There's no mirrors -- this is a sports arena, you know. It's me and Debby Boone, Marie Osmond and some black woman I don't know all in one room. They had these buckets full of ice sitting around, so I just emptied one bucket and made it into a wastebasket."

Sinatra, wearing a windbreaker and identification tags around his neck like everyone else, wandered up and down around the stage, occasionally whispering a direction to a performer. Sinatra invited area families of the hostages, whose imminent release from captivity promised to throw yet another unknown into the scheduled events, to attend the rehearsal. The families, including Penne Laingen and Elisa Moeller, refused to be interviewed but seemed to enjoy the run-through.

Arrangements were made to interrupt the show with breaking news of the hostage situation if necessary.

The arena floor, normally used for hockey and basketball games, was transformed with a small square stage in the center of the floor, decorated in red, white and blue and banked with flowers. Workmen continued to decorate the stage as the rehersal was in progress.

Jimmy Stewart, who was to perform a reading with Gen. Omar Bradley, sat in the audience for a while even though he did not have to rehearse. "I've memorized most of it, but they'll be cue cards," said Stewart. He left to attend a reception for senior and handicapped citizens.

"It's perfectly natural for Ron to emphasize this [show business]," said Stewart. "He's very much part of Hollywood and it's not like him to just sweep it aside."