"You don't see Pavarotti in jeans and a T-shirt," said Oksana Protenic, doctoral student from Laurel, Md. So at 4 in the morning yesterday she entrusted her evening dress to her husband, pulled on slacks and a sweater, tossed curling iron, cosmetics and spray perfume in a sack and fed the cat. By 6 a.m. she was first in line for standing room at the opening of the Metropolitan Opera series in Washington at the Kennedy Center this week.

While Pavarotti was the elixir that inspired Protenic to get out her strapless, others at last night's performance of "L'Elisir d'Amore" by Donizetti knew that Monday-night openings are traditionally dress-up occasions at the Met. Always black tie for the men, and for the women very extravagant (though in recent years short) gowns.

But in Washington, dressing up, particularly for the Kennedy Center, has continued to mean long dresses and that's the way it was last night. A small proportion of the men in black tie, a lot of women in long dresses. Just a handful in the very spiffy new short gowns.

Among those who opted for long dresses was Marta Istomin, artistic director of the Kennedy Center, in a deep red chiffon gown with shawl. In shorter lengths were Ina Ginsburg in an ivory satin dress by Emanuel Ungaro, Peggy Crosby in a mid-calf dress by Rodriguez and Monica Greenbert in a vintage Yves Saint-Laurent chiffon print.

By curtain time Oksana Protenic had turned in her casual clothes for the black silk strapless dress, curled her hair and refreshed her makeup. "Once you've seen him (Pavarotti), you ar hooked." she said. "It just wouldn't be right for me to show up any other way."