Before the cast of "The Little Foxes" even got to their party last night, they had an abbbreviated one with a president who's been to a few himself. Ronald Reagan came backstage, squeezed hands, told Elizabeth Taylor she was wonderful as Regina, then waved merrily goodbye.

The cast waved merrily back, like family to departing kin.

"Drive carefully," called out Maureen Stapleton. She sounded like a doting aunt, which is what she plays in the show.

Then the presidential limousine went zooming back to the White House. Everybody else's went zooming toward Pisces in Georgetown, perhaps the real show in town last night.

You could see Liv Ullmann talking in the corner with her agent, Valerie Harper putting on lipstick in the bathroom, Lillian Hellman smoking Marlboros at her table, or Howard Baker emitting one-liners near the bar.

"I know her as a Senate wife," Baker said, meaning Mrs. John Warner (R.-Va.). "I think her second career is coming along quite well."

"Weren't you bothered to hear her say in the play that she wanted her husband dead?" somebody at Baker's elbow asked.

"No," said Baker. "But I bet John was."

"Only worreid me," responded John Warner, "when she was rehearsing at home."

By this time, after 45 minutes of rubbernecking in the direction of the door, Taylor had arrived. So had the emeralds around her throat.

"How'd you think you did?" cried a voice in the crush.

"What?" she yelled back.

"How'd you think you did?"

"What?"

"HOW'D YOU THINK YOU DID?"

"Oh." A slight pause. And then, responding with some of Regina's wrath: "I don't know."

"She's petrified," said Teresa Heinz, Taylor's friend and georgetown neighbor. "I mean, she is petrified."

A few others in the cast weren't exactly calm, either.

"I can barely remember my own name," said Stapleton.

"I think it went well," said Hellman, who wrote "Little Foxes" when she was 33, "but I'm too nervous at openings to know how things go."

This particular cast party was a snazzy one as cast parties go, although it was noticeably devoid of the Reagan administration members who has dotted the theater. Still, there were a few senators and, as usual on the Washington party circuit in mid-March, plenty of people with tans acquired from trips to this Caribbean island or that. Besides looking glamorous, the tan also provides at least three minutes of vacation chitchat.

Some 500 people were expected at the party, but by midnight, it looked like it was a lot closer to 200. Nonetheless, the black ties and sparkling gowns were enough to impress two young men lollygagging with drinks at the top of some stairs.

Young man No. 1: "Well, here we are at a social party."

No. 2: "Oh, we're doing well."

No. 1: "Doing well. Getting up there."

One of the more interesting developments during the evening was a juicy rumor that Richard Burton, who numbers among Elizabeth Taylor's previous husbands, was at the performance.

"Oh, no," said Zev Bufman, the play's produced. "He's in Los Angeles, doing 'Camelot." He's not here."

"No," added Michael Valenti, a Broadway composer, "but Eddie Fisher is."

Alas, another false alarm.