Every night, Tamatha Duncan kneels by her bed to pray. She gives thanks for the nice day she's just had, for her Grandma and Grandpa, for all her friends at preschool.

"And dear God," she says finally, "will you please hurry up and bring my Mommy and Daddy home?"

Tamatha knows her parents are in a place called Saudi Arabia. It is "far, far away," she says knowledgeably. But Tamatha is only 3 years old, and it is hard for her to understand the recent dramatic changes in her life.

Since August, she has lived in Rockville with her grandparents, Ed and Gretchen Duncan, a couple in their mid-fifties who had thought their child-rearing days were past.

Their son, David, 27, an Army sergeant, and daughter-in-law, Tami, an Army medic, are both stationed in the Persian Gulf with the 24th Infantry Division. No one knows when they will return to reclaim their child.

"She wakes up in the middle of the night," Gretchen Duncan said of Tamatha. "She'll wake up crying, 'Mommy! Daddy!' and I'll look at her and say, 'They'll be home.' And she says, 'Someday?' And I say, 'Yes, baby, someday.' "

It has been a poignant aspect of this war, the children of military families left behind as both parents serve with allied forces in the Persian Gulf War. And Ed and Gretchen Duncan, like other relatives, are not only worrying about the welfare of their son and daughter-in-law, but also having to worry whether Tamatha is eating enough carrots, whether she is happy with her playmates, and that she doesn't see them cry.

"The bad part about it is, being a grandmother is the greatest blessing in the world and being a parent is work," said Duncan, who stays home with Tamatha while her husband goes to his electronics job. "You have to say no. You have to say, 'If you do that again, you're going to have to go sit in your chair.' And all the time, your heart is breaking, because all you want is to pick her up and hug her."

Tamatha has been with her grandparents since that hectic week in mid-August when her parents were suddenly dispatched to Saudi Arabia from their base in Fort Stewart, Ga.

The change came so quickly that one morning: Tamatha's mother dropped her off at the babysitter; that afternoon, her grandparents, who had hurried down from Rockville overnight, picked her up. She did not understand what had happened.

"We told her that Mommy and Daddy are soldiers," Duncan said, "and there was a bad man who hit people. She said, 'Oh, yes, like so-and-so,' some kid she knew at day care. We said that when the man is good, they can come home. That seemed to satisfy her."

Now, Tamatha, a friendly, energetic child with brown eyes and bangs, uses her play phone to hold imaginary conversations with her parents. ("Hi, Daddy, I've been good . . . . ")

At noon each day, she stands at attention and salutes when a local radio station plays the national anthem, requiring her grandmother to join her.

For a while, Tamatha fretted that the photographs her parents sent her from the war zone did not include any of the two together; she was comforted when the couple, who are stationed miles apart, were able to get together for a few minutes at Christmastime for a snapshot.

She shows it to all visitors. And she talks animatedly about that uncertain time of reunion that she calls "someday." ("Someday, I'm going to go to the beach with my mommy and daddy and then we'll . . . . ")

Gradually, the family in Rockville is learning to cope with a situation they cannot change.

Gretchen Duncan, who sometimes finds herself chasing a shrieking Tamatha across her yard, says dryly that she's had to face the fact that she is no longer 20 years old.

She's found herself consulting young mothers about what to do, for example, about Tamatha's sleeping problems. And even though she has always hated to play with dolls, she gamely allows Tamatha to serve tea to her and a dozen different ones, all with specific names.

But still there are times when the child seems overwhelmed, confused, unbearably sad. And that is when her grandmother feels most helpless.

"Sometimes she'll be crying, 'I want my Mommy' and 'I want my Daddy,' and I don't know how to make her feel better," Duncan said. "It's not a boo-boo that Grandma can kiss and put a Band-Aid on. And oh, dear God, how I wish I could."