Open Monday, 11:30 a.m. to 7 p.m.; Tuesday through Thursday, 11:30 a.m. to 11 p.m.; Friday and Saturday, 11:30 a.m. to 2 a.m. No credit cards. No reservations.

We all know about lunch. In fact, we all know too much about lunch, that daily break in routine that in itself becomes routine. The lunch break, the working day's big chance for adventure, is also the make-it or break-it time for a substantial proportiom of downtown restaurants. Thus they, too, fall into routines, daring not the risk of losing the hamburger crowd or the chef-salad diehards.

But downtown - Washington's old E and F street department srore corridor from Hecht's to Garfinckel's - is making a lunchtime comeback. Not only are there new restaurants, but new kinds of restaurants, and in one case a renewed kind of restaurant. Here are three that might even eat into the Reeves routine.

Music was apparently the creative force that started D. C. Space and weekend evenings it upstairs room is devoted to love music, much of it billed to be in the Afro - American tradition. But no lesser creativity plays in the kitchen, which turns out for the downstairs dining room imaginative, finely crafted soups, sandwiches, salads and pastries billed to be in the natural food tradition. What tradition. What that means is that vegetables are fresh, the soups started from scratch in the kitchen, the turkey baked and beef roasted in that very place. It menas that creative energy has gone into desinging into the limited menu things like peanut butter and banana with granola fruit butter, molasses or honey on whole wheat bread; or another sandwich with alfalfa sprouts, mushrooms, avocado, scallions, tomato and vinaigrette . You never can tell what such as artistic bent will achieve - one day a sandwich of potatoes with onion sauce. The club sandwich is made of turkey and roast beef - both expectionally good - rather than nitrite laden bacon. But the sandwich art achieves its finest moment at D. C. Space with a sandwich of monerrey jack cheese grilled with guacamole, mushrooms and tomato on whole wheat bread. Soups are personal statements, hot and spicy and good; salads are imposing, served with inspired dressings like dill yogurt or be a quarter pound of cheese. And dessert, well, there is always room in the culinary art world for another, nutmeg, and this keeps company with very good coffee, fresh apple cider, bottled waters, beers, and wines priced as low as anybody had yet dared in a restaurant here.

There is room to stretch in this slightly bare space with its high pressed-tin ceiling. The setting encourages stretching your mind, for people are often seen reading and writing as well as eating. Self expression is even possible in the choice of the style of table on which you eat: there are dinining room tables, side table, office tables, home tables, with or without red checked cloths, their chairs being movie theater discards, bentwood, church pew-style benches, booths, or lunch countter chrome stools. The walls are hung with a changing show of avant-grade art - real art, not restaurantized print's - and instead of Muzak, serious contemporary music comes through the high quality speakers. The service has not a professional tone, but it sure is friendly, with as many as three waiters wandering by to see how you are doing what you might want. The prices, too, are charmingly amateur, with sandwiches from $1.10 to $2.10, the crab and avocade salad being the biggest splurge at $2.50. Soup, small salad and half of the sandwich du jour comes for $2.50. At D. C. Space, even the bill is music to your ears.