Eben D. Finney III, who was graduated from Washington and Lee University and described himself as "old enough to know better," went to the inaugural anniversary ball at the Corcoran Museum last night with Melanie Parker, who is a legal researcher at the law firm of Covington & Burling and a 22-year-old graduate of Mt. Holyoke College.

With them were Charles Bourget, a 29-year-old marketing consultant who went to Trinity College in Hartford, Conn., and Shelby Strudwick, a 22-year-old graduate of Smith College who works for the Talbots clothing store on Massachusetts Avenue.

They were just four of 1,200 young Republicans who last night celebrated the first year of their party's reign.

"At work I didn't tell a soul I was going," said Strudwick. "You feel that other people might find out and be slighted. But then I told one friend, and she told everybody, and then they came up and said, 'Oh, what are you going to wear?' And I said, 'A long black taffeta dress.' You will not find this dress at Talbots. You can find it in New York. It was made for me."

"Since I'm going to be on the Rugby Ball committee in March," said Parker, "I'd say this isn't as big a deal as that. But this is big for right now."

"Next week we're all going to the Snow Ball in New York and Lester Lanin is going to play," said Strudwick.

"What about the Oxford Regatta?" said Finney. "Or the Annapolis-Newport race?"

"Charles was asked to crew for that," said Strudwick.

Almost exactly at this moment, Vice President George Bush arrived. He'd just been to the Eagles' inaugural anniversary dinner at the Washington Hilton. "This place looks like a lot more fun," he said to the crowd. "And a lot more action."

Few would have disputed him. The crowd noisily crammed into the marble corridors of the museum. Tickets were $20 apiece. Most worked for the campaign, transition or on the inauguration. Now they've been neatly dispersed throughout the agencies and departments of the U.S. government. Many felt Reagan is doing "fabulously" -- as 23-year-old Janice Golec of the Department of Housing and Urban Development put it.

Ask about unemployment, the recession, the federal deficit and the temporary granting of tax-exempt status to racially discriminatory schools and the answer, in this case from 23-year-old Abbie Weist of HUD, was: "Okay, we've only been in the administration for one year. It's hard to take a 40-year period and change it around."

The party was organized by the Anniversary Committee, a group of young Republicans who decided at an anniversary election party on Nov. 4 that it would be a great idea. Last night they marveled at the turnout, which attracted people from across the country.

There was 24-year-old Loreta Burlingame from Dallas, for instance. She was talking to a liberal Washington lawyer who once worked for Sen. Edward Kennedy's (D-Mass.) presidential campaign and begged that his name not be used. "I'm not here," he said.

"I think there are a lot of people here who believe in carrying their own weight in society," said Burlingame, who said she was an Ayn Rand follower. The reporter then asked for the spelling of her name.

"Get her phone number, too," said the liberal lawyer.

"I don't go out with liberals," Burlingame replied. "Besides, you're probably married."

"Separated."

"Ohhhhhhh. That's the usual."