Exotic images filled the halls of the U.N. General Assembly yesterday afternoon. Like Rod Stewart, who came in red satin tights and hair that looked run wet through a light socket. Or Olivia Newton-John, so perfect in her pressed jeans and pinstriped shirt rolled to the elbows. Or Kris Krfistofferson, narrow and Jack-Daniels throaty (though he was slugging Perrier) with a T-shirt that said "Muhammad Ali training camp."

David Frost, the host, was there in a crisp accent and suit, and Henry Fonda, a special guest, was there in an old corduroy coat. The Bee Gees came, and so did Robert Stigwood and Andy Gibb and John Denver and Earth, Wind and Fire and Rita Coolidge and the Fonz and Abba -- who were recently reported, in terms of profit, to be the largest corporation in Sweden -- in fact, everyone who had promised he or she or they would come, with the notable exception of Elton John, who canceled at the last minute. But the galaxy was so great, you hardly noticed one eclipse.

"I dunno," said Gilda Radner, sounding if not looking like RoseAnn Roseannadanna. "I was just walking by the U.N. and somebody jerked me in." That was not the truth.

The occasion was a final rehearsal for a multimillion-dollar TV benefit, to be telecast in America tonight on NBC at 8, called "A Gift of Song -- The Music for UNICEF Concert." The concert inaugurates the U.N.'s International Year of the Child and eventually will be beamed around the world from Bangkok to Nicaragua. By taping time last night, Paramount Television Distribution announced it had signed up more than 40 countries for telecast. "All of them will see it in prime time," said Jack Ling, UNICEF's director of information. "So you can imagine the mathematics."

Which at best is only half the mathematics. For the special aspect of this fund-raiser is that each of the "founder-composers" participating in the concert has agreed to donate all future rights from the number he or she or they perform "in perpetuity" to UNICEF.

In some cases, that is a clobbering donation. Kristofferson and Coolidge, husband and wife, premiere their newest song, "Fallen Angels," on the program, while John Denver has decided to turn over all profits from one of his biggest hits -- "Rhymes and Reasons."

The Bee Gees, who along with Frost and impresario Stigwood put most of the program together, are donating rights to their monster hit, No. 1 this week, "Too Much Heaven."

Last night's taping was attended by a curious melange of audience: the usual young rock concertgoers (most of whom had won their tickets in a citywide radio contest), who sat on the main floor at long tables marked Cyprus and Guatemala and Guyana, and a straight audience of U.N. staff and their families. There were a number of U.N. ambassadors present and a sprinking of New York celebrities such as David Hartman, of "Good Morning America," who didn't stay around for the special-invitation party afterward.

Henry Fonda, designated a co-host, got a standing ovation when he appeared on stage. He read from the "Diary of Anne Frank" and visibly moved the audience.

Ania Chowaniec, 14, who immigrated to America from Poland with her family three years ago, didn't have a ticket to last night's show. "I groveled. Begged. Got down on my knees and pleaded with two security guards," she said. "I can't believe it worked!" After the show she and two pals stood at the stage door and collected autographs. They got Andy Gibb, the Bee Gees, Kristofferson. They held their signatures aloft like trophies.

At the end of the evening U.N. Secretary General Kurt Waldheim addressed the gathering."I thank you for this beautiful evening," he said, adding that millions of poor and suffering children around the world were to be the true beneficiaries of the night.

In the afternoon, there was a general air of good feeling and not-too-camouflaged chaos yesterday in the soaring, brightly lit assembly hall, which has known its raised voices through the years, not all of them mellifluous. There were uncounted calls for "level" and orders to "re-cue the track." Backstage, ordinary people with important-looking badges comingled with the superstars, who were watching on monitors or standing around eating sandwiches and looking very used to this sort of time ooze.

In the center of the disarray, two men played backgammon, oblivious to all else. Nearby was a sign that proclaimed in bold lettering, "There will be limos standing by for errands. Do not take car without informing Ray."

The biggest crush was trying to get into the elevators to get to the assembly hall. It was worse than getting a table at Elaine's on a hot night. Everybody who was the least somebody seemed to be clutching a ticket to the rehearsal. "Visual media," with bags of clunky camera equipment, were ubiquitous. Everyone seemed a potential celebrity. "I've been working here 6 1/2 years," said a U.N. staff carpenter, a man from Bogota, Colombia, named Adelphio; he had knocked off to come and watch the goings-on. "I think this is worse than when the ambassadors are here."

The stage was a mini-fortress of equipment -- speakers, pianos, electric keyboards, drums, microphones. Overhead were great moody cutouts of children from around the world. John Denver -- who looked anything but a country boy in his belled slacks and black patent loafers with gold buckles -- sang his number on a raised platform amidst the cutouts. When he was done, he said, "You know our gift of song is a kind of investment, the same investment our parents gave us... what a pleasure this is."

Henry Winkler, who had on a letter sweater and a slightly peaked face, was continually besieged by some of the children brought in for the program. "No, I won't do the Fonz," he said. "And yes, I think Kris Kristofferson's voice is neater than mine. What else do you want from me?"

Jeannie Dubensky said she thought Kristofferson's voice was neat. She is in Manhattan Passenger Sales for TWA, the airline responsible for bringing most of the stars to New York for the benefit, and she said she wasn't leaving till she got up close to the singer. Last Saturday she had met Rod Stewart's plane at the airport, but that wasn't a lot of cheese. "I wasn't even sure what he looked like," she said. "But then 9, 10, 11, 12, 13, 14, 15 guys in silver lame jackets got off the plane and I figured that was them."