Willie Stark, Act IV

When the curtain went down after the third and last act of "Willie Stark" at the opera house last week, the curtain went up on act IV, in the lobby outside the first tier.

This was the post-premiere party, a ritual where rarely is heard a discouraging word, and many guests no matter what they thought of the show, pay extravagant compliments to the producer (in this case, Hal Prince), the composer and librettist (Carlisle Floyd) and all the cast.

"I thought it was marvelous, just marvelous," said one woman to Prince. He beamed. "Just exquisite," she continued, walking away.

"Well," she sighed moments later, safely ensconced on the other side of the room, "Stravinsky it's not."

"I don't have anything to compare it with," hedged playwright Larry L. King, who has written a one-man show on Huey Long that he's considering turning into a musical. "Now, if you want to talk about Willie Nelson . . ."

"I liked it," said Texas congressman Charlie Wilson. "I saw 'Requiem.' Liked that too . . . Well, maybe it was a bit heavy for old Charlie."

Robert Penn Warren was in the audience and at the party, too. Some said he thought the show, a three-act opera adapted from his book "All the King's Men," was a bit "compressed." But, sitting placidly at an out-of-the-way table, he demurred, and talked instead of the rigors of his trade. He's not thinking about novels so much anymore, and spends most of his time on his poetry.

"When you get to be a certain age, to start writing a novel is like going to jail for three years. But when you start a poem, it's like going for three months. Or maybe," he said, his face brightening, "for three weeks."

The opera was a hit with at least one member of the audience, an elderly woman who was seen lingering over a candy-seller's tray before the house doors were opened.

She dawdled and then walked off without buying any Jordan Almonds, or even a bag of peanuts. "Enjoy the show," the candy-seller called out.

"I'd better, dear," the woman replied. "I'm Hal Prince's mother." The CARE Contingent

On any given evening in Washington, you can find a ballroom full of formally clad people gathered together for charity's sake.

Such was the case at the Organization of American States, where Alejandro Orfila opened the doors for a CARE gala, celebrating 35 years of little brown packages and, these days, Third World development plans.

The evening started with dinners at 15 embassies. Not everyone had to scurry all over town, though. If you really rated, you ate at the OAS, and so didn't have to rush back there for the reception.

Charity galas are multipurpose events. They raise money for good causes, give people a place to wear their fancy clothes, and give the able-bodied women and men who organize them a taste of madness for a week or so, which can be bracing.

But for some in the audience, the CARE ball wasn't just any evening of charitable cheer.

Leo Welt, a Washington Businessman, received one of the first CARE packages as a child in war-torn Berlin. He came to express appreciation. "I remember. I got a message that there was a package for me, and I went to pick it up in Steglitz, in the American district. It was so heavy. Filled with powdered milk, margarine, eggs, flour, sugar. And a carton of cigarettes. They were more valuable than money. They were money." The package came from "some lovely family in Nebraska. I took the package home." But not to his family.

"No, they were all gone," said Welt. "I took the package to my grandmother. They were great, those packages. And I got a lot of them, too." Goodbye to All That

The lunch for the cabinet wives at the Phillips Collection early last week was billed as a quiet little affair to bid farewell to Renoir's "Luncheon of the Boating Party." Museum director Laughlin Phillips presided with his mother, Mrs. Duncan Phillips. As it was pouring outside, she had on galoshes, which she kept on throughout the afternoon.

"I imagine some people had to swim to get here," said Laughlin Phillips, with characteristic laconicism. The rain didn't keep anyone away, though.

"Don't worry about blank spaces on the walls," said Nancy Hanks, exhoncho of the NEA and now a loyal soldier on the Phillips Committee. "There're lots of nice things in storage." Seventy-five nice things, with luck -- enough to fill the gaps left by the pictures that will go on display July 4 in San Francisco.

Goodbyes, as it turned out, were a bit premature, because most of the cabinet wives had never been to the Phillips before, much less stood before the resplendent Renoir. (It's just been cleaned and practically glows.) But they managed to rustle up some semtiment, though they stopped short of waving their dinner napkins.