The name had a cachet about them that could make you do a double take.

"Mrs. Hamilton Jordan, Mrs. Frank Moore, Mrs. Jody Powell," it began, "invite you to an unusual event to benefit the new Capitol Children's Museum . . ."

In the 10 months since Jimmy Carter came to town, inner circle administration wives rarely had been seen on the charity circuit. Rosalynn Carter had made her position on benefit-backing clear from the beginning: Unlike some of her predeccessors, she would not lend her name as a come-on. White House wives seemed to be following suit.

Now, in bold-faced type, here were Nancy Hordan. Nancy Moore and Nan Powell - sometimes called "the three Nans" - whose husbands are Carter's top assistants, heading up an afternoon of dancing bears. Cossack riding and high-wire acts at the Moscow Cricus.

In a town where underachievers can be viewed with as much suspicion as overachievers (it's not playing the game, remember), what could it all mean?

"Some people might attribute other motives," says one committee member, "but believe me, they really don't exist. The museum is such a low-key, out-of-the-mainstream place which they all feel is worthwhile. And they were actually, well, naive about how lucky they felt they were to get involved."

It was, says this same source, "the luck of the Irish" (or in this case, of the museum) that the Moores lived next door to Judith Nelson. She had been invloved in it from its inception. Her daughter Hilary was the Moores' babysitter and it was just a "simple, nice, neighborhood way" of passing the word.

"You can't know Judy Nelson two seconds without knowing about the museum," says Ann White Lewin, the museum's director.

"I slid into it that way," says Nancy MOOre, a former schoolteacher whose four children - Brian, 6, Hank, 8, Courtney, 10, and Elizabeth, 11 - are what she calls "the center of my life."

Beofre long also interested were two other former schoolteachers. Nancy Jordan, whose teaching specialty was handicapped children, and nan Powell, whose daughter Emily, 11, like the Moore youngsters, is a playmate of Amy Carter.

At a luncheon set up by Lucille Graham in September "we really kicked the idea of a fund-raiser around," Moore remembers. Nancy Jordan and she had both done a "little fund-raising" in the campaign and liked it.

At the luncheon, and subsequently other events designed to accquaint various groups with the fledging museum (Nan Powell once business people), the big question was how to keep it open. Lewin says. Operating on some corporate seed grants and donation from individuals and a few businesses, the museum occupies four former classrooms made available by the D.C. Board of Education at Lovejoy School, 12th and D Streets NE.

The three Nans agreed to lend names and elbow grease but wanted help from someone more familiar with Washington's private and corporate pocketbooks. Lucille Graham, whose husband (CBS correspondent Fred Graham) had known Esther Kefauver, proposed veteran fund-raiser Coopersmith.

Lewin is careful to give equal billing to all involved in the Sunday afternoon Capitol Center benefit ($25 for adults, $10 for children, with a post-performance reception thrown in). "Everybody's worked," she says. "When you're building a new institution, you can never point to one person and say there's the answer."

Still, response to invitations personally signed by the three Nans has been duly noted by some on the committee. And while Nancy Moore says there haven't been many requests - "just a few, really" - from other Washington chariries to lend her name in the 10 months she lived here, the triple debut of Nancy Jordan, Nancy Moore and Nan Powell into the wonderful world of Washington benefits is not lost on anyone.