Secretary of Defense Caspar Weinberger made it with 15 minutes to spare, coming in the door right behind Eunice Shriver, who all but flung her full-length mink at the coat check attendant before racing upstairs to shake hands with Argentine President Raul Alfonsin.

Meanwhile, on the next street, Sargent Shriver had parked his car and was looking for a shortcut into the Argentine embassy. He chose the alley and was last seen disappearing into it, triggering who knows what strong-arm reactions by an always nervous Secret Service detail assigned to protect visiting heads of state.

The names of the principals may have been different, but otherwise last night it was your typical embassy reception. Bedlam.

Seemingly oblivious to it all was Alfonsin, still euphoric over the reaction he got earlier on Capitol Hill, where he addressed a joint session of Congress.

"Beautiful, beautiful," Alfonsin said in Spanish.

"So spontaneous, so warm, he was very touched," said Argentine Ambassador Lucio Garcia del Solar. "He had no idea it would be that way."

Others at the party weren't the least surprised.

"The White House is trying to signal Chile that, as John F. Kennedy once said, 'We reserve our special friendship for democratic governments,' " said one veteran political observer.

"He's a very special person," said U.S. Ambassador to Argentina Frank V. Ortiz Jr. of Alfonsin. "He got along extremely well with the president."

Like everybody else throughout Alfonsin's two-day Washington stop, Ortiz voiced concern over Argentina's economic situation. Was the United States going to help?

"It's an internal matter," said Ortiz. "The Argentines are taking their money out of the country . They don't have the confidence to invest in their country. But this trip will help a lot, I think."

Not all the talk focused on Argentina, however. Over in one end of the dining room White House chief of staff Donald Regan was chortling over how "we scooped the press today on Bill Brock" as President Reagan's nominee for secretary of labor.

It raised the question of who had been circulating Ed Rollins' name for the job.

"Rollins," said Regan, laughing heartily, insisting that Rollins had not known he was out of the running until Regan called him at 11:45 a.m. to tell him the news.

Which of course raised one of the evening's most provocative questions. Ambassador Ortiz voiced it.

"What are we coming to," he asked, "if we have a White House that doesn't leak?"

Regan just grinned.