''I just want to break even, but this is bigger than bucks,'' Mr. Joel told reporters after the concert. ''People in the audience want to be in the dark. They want to get loose.'' A Pause That Refreshed

At the end of ''Just a Fantasy,'' Mr. Joel conferred with his band and then banged on a set of drums before resuming the concert.

''It was a real prima donna act, but I have to protect my show,'' a perspiring Mr. Joel said later as he sipped a glass of water, his wrinkled blue shirt outside his trousers.

''I've been on the road for 11 months,'' he said. ''It's difficult. I'm running ragged.'' He also complained that his throat was hurting him and said he had seen a doctor.

The Soviet audience, which filled Moscow's 20,000-seat Olympic sports complex to capacity, appeared unsure about whether Mr. Joel's tantrum was part of the show, but they remained enthusiastic. They thronged to the front of the stage during the second half of the concert, jumping in the air and applauding. A Cool Reaction