Atmosphere: An old-fashioned grandmother's house, complete with antiques and a china collection.

Hours: 11:45 a.m. to 2:30 p.m. and 5 p.m. to 8:30 p.m. Tuesday through Saturday; noon to 8:30 p.m. Sunday: closed Mondays and the last two weeks of August.

Price range: $8.75 to $12.75 for a complete dinner, children's dinners at half-price.

Reservations: A must. Plan ahead for holiday times.

Credit Cards: American Express, Visa, Mastercharge.

Special facilities: Dining rooms not easily accessible by wheelchair, but mention special needs when you make reservations and management will assist you; parking in adjacent lot; boosters and high chairs available; wine list but no soft drinks.

January 1981 is not too early to begin planning a visit next Christmas Mrs. K's Toll House, the 50-year-old institution at Dale Drive and Colesville Road in Silver Spring.

Mark Nov. 1 on the calendar to remind you to call and make a reservation for the restaurant's Christmas season, when Mrs. K's perennially is booked solid. From early December through mid-January, hundreds of Christmas ornaments made by Mrs. K's employes beguile and delight adults as well as children.

Once an actual toll house for carriages passing from Montgomery County into Washington, Mrs. K's is full of antiques and displays collections of Staffordshire china and Micholas Lutz glass. It is not exactly the first place that comes to mind for dinner out with the children, but children are welcome and treated well there.

Especially at Christmastime, when the whole restaurant looks like a stage setting for a Nutcracker production.

Outside, the roof was adorned with Santa and his raindeer; inside the entrance was an enourmous gingerbread house. In the three dining rooms there were sparkling lights, natural wreaths with red ribbons, Santa Claus and model villages.

In one room, diners sat beneath a shower of bright bells suspended from colored ribbons; in another, a Santa-in-snow scene dominated the fireplace. In the room where we were seated, hundreds of decorated cookies were hung overhead, and brightly lit trees decorated the walls.

Ah yes, the food. At first glance, the menu prices seem high, with everything in the $9-$11 range. Meals for children 10 and under are half-price, and there is a mimimum charge of $1.50 ($2 on Sunday) for children under 10 even if they share another's meal. The menu is not lengthy. cEntrees are straightforward American dishes -- mostly roasted meats, in addition to crab imperial and steak.

But after we had been served a well prepared soup-to-nuts dinner for that single price, including beverages and dessert, we thought Mrs. K's a good bargain. In the tradition of a country inn, Mrs. K's sets forth a variety of courses and extras that leaves patrons with a sense of well-being and plenty. And they do it better than many a local country establishment.

Dinner began with a choice of appetizers. We sampled fresh fruit cup as well as gazpacho and vegetable soup, both rich with homemade flavors. Our waiter appeared next with a platter of salad greens and cottage cheese, shredded carrots and celery, wedges of tomato and sweet onion rings, colorfully heaped around a bowl of dressing. We served ourselves with the stack of bowls he left us.

Our entrees arrived just when were ready for them, accompanied by fresh rolls hot from the oven and a relish tray containing a delicious homemade cranberry sauce.

Roast turkey and dressing, $9.95, was a success, as were the fried shrimp dinners our three daughters chose. Roast duck, $9.95, though platable, was a bit undercooked, and the mashed potatoes with it came out of a box. Otherwise, our main courses were fine. Our 10-year-olds especially enjoyed one of Mrs. K's extras: smallscoops of lemon sherbet served between courses.

For dessert, Mrs. K's offers 10 choices, mostly ice cream dishes and baked-on-the-premises pies and cobblers. The girls applauded their chocolate sundaes, and the pecan pie with a light crust was fresh and delicious.

The final course was the check, $41.27 plus tip, which seemed fair exchange for lovely food, good service and a fairyland setting. Christmas is a wonderful time to go to Mrs. K's, but any special occasion will do. Think spring, when Mrs. K's gardens abound with flowering shrubs, trees and bulbs.