Mary Kennedy Waldo, honorary grandmother to half of Arlington County, turned 100 yesterday, surrounded as always by children.

Mrs. Waldo took all the hugging and kissing in stride, calling one by one the names of people -- some of them now grandparents -- whose diapers she had changed and whose hurts she had kissed away as much as 50 years ago.

"No, I'm all right," she said to one of them when he bent over her wheelchair to ask whether she was tired. "I've been looking forward to this for a long time."

When some of the children who serenaded her began to lag in the middle of "Small World" she unobtrusively brought them back into time with sure and delicate motions of her hand. Some of those present credit her with having ease their lonely childhoods with similarly subtle support. "I was a rotten kid," one middle-aged man said. "I didn't have any friends, not even myself, but Nana always had time for me. She listened, she understood, and she never criticized."

"Nana" Waldo has spent the last decade at The Hermitage in Alexandria, but for some 40 years before that lived in Arlington's Buckingham Apartments, one of the huge single-age, single-class suburban "ghettos" built in the 1930s to house the bright young people FDR brought to Washington. She was one of the few old people among all those acres of young parents; to their children she gave what she could of a sense of community and the continuity of generations.

The span of that continuity is breathtaking: She was one of the babies William Jennings Bryan dandled on his knee when he came barnstorming through Franklin, Va. She grew up there in the home of Judge and Mrs. Pennybacker, who took her in when her parents died of pneumonia in Harrisonburg, Va. Her father, William S. Kennedy, was a language professor from Georgia who came marching north to the Battle of Newmarket. He met Mary Van Pelt during Gen. Beauregard's campaign and returned to marry her after the Civil War.

In 1904 Judge Pennybacker's ward married dentist Willian H. Waldo, who kept on filling teeth during the Depression although most patients could not pay, and who died in 1934. There were two children: Katherine, who died in 1952, and Roswell, now a retired lawyer in Alexandria, who was at The Hermitage penthouse yesterday trying to keep his mother from being overwhelmed by all the attention and also to set the record straight. "She tells wonderful stories, but not all of them are right," he said. "She hasn't written a book, for instance."

What a pity. Nana's stories, which had only a nodding acquaintance with Mother Goose, are universally remembered as believable and gripping and scary until everything turned out all right in the end. There were no heavy morals; she knew the kids had enough to worry about already.

She was a little worried about the kids who came to the party yesterday, who seemed a little intimidated by all the strangers. They had been brought from a Washington church day school by longtime friend Sandy Ripley, and it did not take them long to cotton to Nana. "Do you have all the children's names?" Mrs. Waldo asked the reporter. He didn't, but he went and got them. The children were casual about the spellings but exact about ages, and they were: Helen Hong, 4; Annie Trubach, "3 and 4"; Jed Crandal, 3; Maria Eldrige, 9 1/2; Jessica Ferris, 10; Tanya Delerive, 10; Brian Joseph Ness, 4 3/4; and Sarah Dawson, 6 3/4.

The highlight of the affair was a magic show put on by Robert Berdeen, now a New York actor, who was "adopted" by Nana from the day he was born. On that particular day, as his mother, Millie Berdeen, tells it when pressed, she mistook the labor pains for, er, other pains, and Bobby was born and unexpectedly and informally but very thoroughly christened in a large white china receptacle.

Thereafter, Mrs. Waldo made a point of spending as much time as possible in the Berdeen household, where children -- theirs and many others -- ran at large while the father was usually doing pistol practice in the basement (yes) and the mother was usually selling World Book encylopedias.

I don't know what I would have done without Nana," Millie Berdeen said.

"I don't know what I would have done without Nana," Bobby Berdeen said.

He paid her back a little yesterday, because as long as Berdeen was doing magic tricks, neither of two rival ladies was wheeling Mrs. Waldo up and down the penthouse introducing her, again, to the same people the other lady had just presented her to. Later, Mrs. Waldo collared the reporter again, perhaps remembering him from youth as a person who did not take instruction well.

"You know I'm not the only lady here?" she asked. "Do you have the names of the others?"

Yes, ma'am. The other centenarians at The Hermitage are Virgie Wynkoop, who will be 102 in October; Ethel Hammond, 101 this month, and Lillian Burke, 101 next month. Emily Doue joins the century club in October.

One of the things you're supposed to get when you reach 100 is a birthday card from the president, but Mrs. Waldo's had not arrived yesterday. She did not criticize Jimmy Carter for being unable to make the mails run on time.