In the transformation of Washington from Southern city to cosmpolitan capital, the Brook Farm Restaurant on Brookville Road in Chevy Chase, Md. has endured.

In earlier days it was the Brook Farm Tea House (the remnant of a 600-acre estate first deeded in 1780 to Charles Carroll), a place where Mrs. Franklin D. Roosevelt lunched with congressional wives on food served by "Brook Farm's old black New Orleans cook" at a top price of $1, according to a contemporary brochure.

A 1940s matchcover, part of a collection acquired at a local flea market, was my first introduction to the Brook Farm Restaurant. Then, the matchcover boasted, the restaurant was "Famous For . . . Southern Fried Chicken," among other things, under the ownership of the Jack Davises.

Now, under the ownership of Wolfgang and Christa Erba, the food is German in flavor, but the setting remains vintage American.

We paid our first family visit to Brook Farm, located just east of Connecticut Aveunue, on a recent Sunday evening about 6 and emerged, nearly 90 minutes later, well-satisfied with the experience.

The restaurant was not crowded. There were other families, including one with a young child who was unwiling to remain in his high chair. Various members of his party took turns walking around with him while others ate.

It was the weekend before Christmas, and a large lit-up tree filled one corner of the cavernous from room. We were seated adjacent to it, a location the hostess thought our six-year-old son would especially enjoy. He was also intrigued by the candle wax figurine on the nearby piano, which was not in use this night.

Behind the piano, a rifle rested on deer hooves near the window. Across the room, a stuffed deer-head with antlers stared solemnly from above the fireplace. A spinning wheel sat in one corner near an old crank wall phone.

Hanging from a balcony that spans the width of the room were the flags of Switzerland, the United States, Germany and Brazil - the countries which the chef had worked in, we were told.

The menu featured a la carte appetizers, American "favorities" - from $4.50 fried chicken to $7.75 ten-ounce sirloin steak - and "Continental Specialties - eight dishes ranging from $4.50 for stuffed cabbage to $6.75 for roast duckling. In addition, there are daily specials which are posted on blackboards, from which I chose the goose with apple stuffing.

Children can receive half price half-portions of everything except steak and trout, according to the menu. For our son, however, we ordered a bowl of apple sauce (75 cents) and two potato pancakes ($1.25), which seemed ample for him.He also enjoyed some of the fresh warm bread with crisp crust brought to the table.

With each entree come two vegetables. My wife and I both had salad with roquefort dressing. The lettuce was fresh, the roquefort mixed with a wine and vinegar base. Cherry tomatoes and bits of shredded carrot helped make the salad complete.

My $8.50 goose - the most expensive dish offered - was good. There was more than enough meat and it was well-cooked. The resulting dryness was offset by the moist baked apple slices and tiny grapes. My zucchini squash was delicious, more a ratatouille, with mushrooms and cooked tomato.

My wife described her $5.25 veal goulash as "fantastic", with a delicately-spiced sauce. Her second vegetable was red cabbage, also good. Both entrees were garnished with parsley.

Our house wines, red and white, were satisfactory at 95 cents a glass. The $1.25 apple strudel we shared was good, with a pastry-like crust. We washed it down with coffee and tea.

We found the room to be over heated. Otherwise, service was excellent - paced just right - and the food far above average. Our total came to $20.41, plus $3 for tip.

Open for dinner, 5 to 10 p.m. daily except Monday. Rathskeller downstairs offers somewhat later - blue jeans, sneakers, shorts permitted there. Credit cards. Phone OL 2-8820. Free Parking.