Verdi's "Aida" is practically the last word in operatic crowd pleasers -- as much for its spectacular scale as its quality.

But the capacity audience of 6,500 that turned out last night at Wolf Trap to hear "Aida" with an all-star cast was not pleased.

All had seemed to be going especially smoothly in the cool, serene post-storm sunset at the outdoor amphi-theater until a mere 30 minutes before curtain time. Most of the unusually large crowd was already there and the remainders were lined up on the Dulles freeway.

Then the opera, a repeat of Thursday night's triumph by Sarah Caldwell's Opera Company of Boston, was abruptly canceled. It came as a shock to the growing crowd.

Almost everything was in place. Celebrated soprano Shirley Verrett was there, making her debut in this production of Aida. So was equally celebrated tenor James McCracken as Radames. The sets were in place. Orchestra and chorus were assembled. Only one thing was a hopeless cause -- lights.

Wolf Trap -- like many homes and institutions in the area -- had had its transformer zapped by lightning during the heavy turbulence about three hours earlier.

And the wishful thinking that caused management to avoid biting the cancellation bullet until the very last minute proved fruitless. Even an hour after the 8:30 p.m. curtain time, emergency generators weren't even providing enough light for violinists to have read their music, much less for the principal singers to have groped their ways through the monumental edifices of ancient Egypt that provide "Aida's" setting.

Wolf Trap and the traffic arteries nearby were thrown into unseemly disarray. In its ten years, the place had canceled only once before, and that was not this way.

If you were in the line of cars on the Dulles road, you began to wonder if "Aida" hadn't drawn a larger crowd that Wolf Trap could handle. The movement got slower and slower (maybe a quarter of a mile every 10 minutes) and the line kept growing, perhaps up to three miles. When you finally got up to the gate you ran into two beleaguered young Park Service employes who were warning drivers one by one of the cancellation. "I'm sorry about the mess," said the young lady, "but we don't have any more help."

The gate into Wolf Trap had been closed to avoid further congestion and even a plea to open it to get out a woman who had injured herself was initially refused.

One frustrated man was screaming with the best of intentions to one of the Park Service, "But I came all the way from North Carolina for this." There was nothing they could do to help him.

About all Wolf Trap could do is give refunds on the tickets, yet another blow for its already hard pressed Boston Opera expenditures.