Outside, Georgetown bustles by on a sunny Sunday afternoon. Inside, Debbie Saudek and Katie Mariano, both 10, are stepping out of their fourth-grade routine to spend a day as Mary and Hariot Chew, who lived here with their mother, Cassandra, from 1767 to 1776. Mrs. Chew, a prosperous businesswoman, was a leading socialite in the Georgetown of her day.

The girls have shed their sneakers and desert boots (although not Debbie's striped socks) for old-fashioned clogs, white ruffled caps and blouses and long aprons over long cotton skirts. They're chopping carrots, potatoes, onions and celery for a thick, 18th-century split-pea soup, which Rae Koch, their pretend mother, has already set to bubbling in a big black iron pot over the open fire.

The kitchen is rustic, with a low, beamed ceiling, iron implements, festoons of dried staples and a smoky smell. The talk is of ships coming from England with tea, tallow and fabric for new dresses. It's a Vermeer scene of domestic tranquility.

The Old Stone House, considered the oldest existing house in Washington, is a National Park Service "living history" site; Koch is its manager, and Debbie and Katie are volunteers in its apprentice program.

After cooking, the girls move to the frontroom cabinet shop for sewing with Cathy Ingram, a graduate of Gallaudet College who welcomes deaf girls as volunteers.Working at a wooden table, Katie and Debbie cut bright flowered cotton squares and sew them together into potholders that are quilts in miniature.

Some more cooking, Sunday dinner, a poke around the garden and some time at a spinning wheel, making yard from raw wool, and the girls find that their brief hours in the past have flown.

As Katie and Debbie get ready to change back into their own clothes, they allow that it feels "different" playing a girl from another time. In this peaceful haven in the midst of the city, you look out the window and are surprised to see cars rushing by.

The Old Stone House's apprentice program, for girls 10 to 14, runs only September through April, though volunteers (16 and older) are used year-round. Colonial clothes are provided. Contact Rae Koch, 426-6851, or write to the Old Stone House, 3051 M Street NW. Besides the house, this area boasts a wealth of historic sites where the past can be pursued at its source, and many of them accept teenage volunteers year-round or during the summer. Here's where and how to apply.