"You've delayed and prevaricated long enough," attorney Linus Drinkwater shouted at Impresario Cosmo Maximillian yesterday afternoon at the Kennedy Center, and the audience broke up. The line is not supposed to be particularly funny, but at yesterday's matinee actor Jack Aranson, who plays Maximillian, the title role in Mozart's "The Impresario," had delayed the curtain half an hour.

The theme of the show is the problems involved in putting on an opera, but Aranson came up with one that was not in the script. He had been delayed in Memphis when his flight developed engine trouble, switched to another flight that was also delayed and finally changed into his costume going up into the backstage elevator after a ride from National Airport that reportedly took only four-and-a-half minutes.

To keep the audience happy while waiting for Aransn, Kennedy Center artistic director Martin Feinstein and conductor John Mauceri improvised a preview of the next comic opera in the summer season, Offenbach's "Christopher Columbus," which is now in rehearsal and will open on July 31.

"I told them frankly that I was stalling for time," Feinstein said, "and I threatened to kill time by telling them about all the last-minute crises I have had since I began working with Hurok in 1946. The first one was a Latin American ballet company that was delayed by a revolution."