The lights were out in the coliseum, a videotape presentation about a formerly obscure 35-year-old state senator playing above the crowd on a rented movie screen. At the end of the film, a spotlight cut through the darkness, zeroing in like a laser on the clean-cut young Nathan Miller.

"Brilliant," murmured a young man decorated with several candidates' Wares, "absolutely brilliant. Just like in a movie."

Virginia Republicans have been meeting this weekend to pick a nominee for the U.S. Senate in a convention that has attracted a record number of delegates and which, as theater, will be memorable for the nearly 10,000 participants and observers attending it.

The music, the confetti, the yelling, horn tooting, drum-beating, chanting, flag-waving, drinking, marching and speechifying - not to mention the presence of a real movie star (Elizabeth Taylor) and real television crews - all combined to prove once again that political conventions are events where the art of show business and politics are often hard to separate.

"It doesn't change anyone's mind," said one campaign aide of the floor demonstrations and poster wars, "but people notice it if isn't there."

By late afternoon it was still unclear who would win - former governor Linwood Holton, former party chairman Richard D. Obenshain, or former Navy secretary John W. Warner. Miller, a sentimental favorite, surprised many by getting 251.84 votes on the first ballot but was not expected to win.

Tension increased dramatically after the first ballot, which took two hours to complete.

Cheers from Warner's supporters went up as he appeared after the first ballot results were announced and kissed his wife, Elizabeth Taylor, who was seated in a front-row seat on the first tier. These cheers were answered with waves of rival chants: "We want Dick, we want Dick," and "We want Lin, we want Lin."

Soon it became a cacophony of shouts."On-ben-shain, O'be-shain. We want Lin. We want John, Miller, Warner, Holton, Obenshain."

One of the unusual aspects of this convention has been the presence of Taylor. Apart from the people constantly taking her picture, at least half a dozen Liz look-alikes were spotted throughout the huge hall. They were all Warner supporters. ?Several veteran party workers said that Warner's supporters have attracted significant numbers of new blood to the Republican convention, a clear advantage for him.)

One of the look-alikes, Helen Millar of Fairfax, said she has been wearing the heavy eye makeup she favors for 20 years, having learned how to apply it while "working with Helena Rubinstein in New York years ago." She said she was not trying to look like Liz, although she does not discourage the comparison. "She (Taylor) is now doing what I've been doing all along," she said.

Millar pointed out that she has a beauty mark on her cheek just like Liz. "People think it's fake, but it's not, Feel," she said, grabbing a reporter's hand and rubbing it across the mole.

Another Liz look-alike. Josephine (Nita) Schaefer, also from Northern Virginia, said she has some show business experience of her own. "I sang with Jimmy Dorsey and Xavier Cugat," she said in a Spanish accent. Schaefer said she is now a yoga teacher in Crystal City.

Taylor herself was gamely doing her bit as a candidate's wife, waving, smiling and roaming the floor once or twice with her husband or his supporters. At one point she and Holton happened to be getting into their limousines backstage at the same moment. "Why don't you ride with us, Lin?" she said slyly. (Needless to say, he didn't).

While Liz-watching was a popular game, others took to sailing paper airplanes, which did not please the convention chairman, State Sen. Herbert E. Bateman. "Please discontinue these artful missiles," said Bateman, who is not know for his simplicity of language.

While most of the senior elected officials, such as retiring U.S. Sen. William L. Scott and Gov. John N. Dalton, visited the convention before the balloting began and then left for the afternoon, former governor Mills E. Godwin stayed on. Occasionally leaning against one of the front platforms, the well-tanned patriarch of Virginia politics greeted well-wishers and caregully watched the proceedings. Godwin made the nominating speech for Obenshain, and even received .66 of a vote on the first ballot.

Dalton's family was well represented among the delegates from Radford City, his home town. Three of his four children were delegates and "A lot of cousins and aunts," he said. "We counted them up and we've got someone supporting every candidate," he said.

During the day the music was supplied by a group called the Richmond Pops Band, college students led by Frank Rowley, 64. Rowley was besieged at one point by campaign aides who wanted him to play special songs for which the band did not have the music. "All it has to be is loud and lousy," Rowley shrugged.

The demonstrations were limited to 12 minutes per candidate. The order of nomination was determined by lot, with Holton drawing the first spot, considered the least desirable.

There were slight differences in the demonstration. Holton's people carried more hand-lettered signs - one said "Once upon a time it wasn't nice to be a Republican, but that was before Holton" - and piercing air pressure horns.

Warner had the band play "Anchors Aweigh" and his supporters carried tinkly noisemakers and a bass drum. Obenshain's crowd had small metal clickers that sounded like a flock of crickets.

At an 8th District caucus meeting yesterday morning, Tony Lawrence of Woodbridge said to chairman Barbara Hildenbrand, "You're the most positive person I've seen here who's awake and wasn't up drunk all night. Praise God."

Lawrence, a printer, said he came with five other members of the Sovereign Grace Church. He was carrying the Gospel according to St. John, which he said he would read if the convention got boring. An Obenshain supporter, Lawrence said. "I'm hoping to hold my composure and be a testimony for the Lord . . . Christians have to get more involved in politics."