DISPENSING greasy eggs, hospitality and java, the all- night diner is an ineluctable part of the classic American landscape. Nobody understands the moral imperative of the institution better than those of us who have wandered through this transient, image-conscious, 9-to-5 town, searching for a coffee shop, yearning for a lunch counter, dreaming of a nocturnal hangout like . . . .

The Tastee Diner of Silver Spring. There it sits at the corner of Wayne and Georgia avenues, a ramshackle little place with a wonderful fluorescent glow. The chrome siding is tarnished, the blue-and-white-striped awning is badly tattered and the lettering on the doormat has all but faded, but somehow these imperfections add to the Tastee's appeal.

And inside? Well, Edward Hopper would have had a field day here. Tonight, a sprinkling of what owner Bob Trayner calls "regulars" plunk their backsides down on the red-vinyl-covered stools at the counter. Some will spend the wee hours staring into their beer suds and coffee swirls. Others will trade quips with their fellows or with the diner's two waitresses: Hannah Wade, a feisty octogenarian, and Mae Bush, who still retains her good humor after 30-some years at the Tastee.

Members of downtown Silver Spring's new breed of white- collar employees -- those working the graveyard shift in bland concrete buildings -- settle into the patched old booths and liven up their "dinner" breaks with a Hamburger Royale and a mournful tune from the miniature juke boxes that line the walls. A sharply dressed couple, no doubt on the way home from a fancy affair, share an order of fries.

Engrossed in a paperback and a plate of cinnamon toast, a young woman looks up to notice a bearded man staring fixedly at her from a corner booth. His right hand moves rapidly over a big white artist's sketchpad. Unable to contain her curiosity, she strolls over to his table, and stares down at her handsomely rendered portrait. Smiling broadly, she goes back to her booth, gathers up her things, pays her check, and sails out into the night. DESPERATELY SEEKING SUSTENANCE

Doctors, dieticians and other spoilsports warn that eating before bedtime is the worst thing for the waistline. Unfortunately for some of us, that's just when our appetite is waking up. So, in addition to the Tastee Diner, here's a scattered sampling of late, late lifesavers, for the midnight snack attack a refrigerator raid can't handle:

AMERICAN CAFE -- 1211 Wisconsin Ave. NW (Sunday-Thursday till 3 a.m.; Friday and Saturday till 4 a.m. (337-3600); 227 Massachusetts Ave. NE. Sunday-Thursday till 2 a.m.; Friday and Saturday till 3 a.m. (547-8504).

AMPHORA -- 377 W. Maple Ave., Vienna. The solid suburban American-Greek diner-restaurant. All items on the mile-long menu (eggs to lobster tail) available all the time. Seven days, 24 hours. (938-7877).

ANNA MARIA'S -- After hours Italian. 1737 Connecticut Ave. NW. Monday through Saturday till 4 a.m.; Sunday till 2 a.m. (667-1444).

AU PIED DE COCHON -- Slightly bohemian; bring a wild appetite. 1335 Wisconsin Ave. NW. Seven days, 24 hours. (333-5440).

BOOEYMONGER -- Burgers and other all-American fun food. 5252 Wisconsin Ave. NW. Sunday through Thursday till 1 a.m.; Friday and Saturday all night (686-5805); 3265 Prospect St. NW. Seven days till midnight (333-4810).

GEORGETOWN CAFE -- For a slice of pizza or a slice of life. 1623 Wisconsin Ave. NW. Seven days a week, 24 hours (333-0215).

HERB'S -- The artsy crowd gets hungry, too. 2111 P St. NW. Weekdays till midnight; Fridays and Saturdays till 1 a.m. (333-4372).

HOWARD JOHNSON'S -- Ice cream and apple pie and tradition under the orange roof. 2601 Virginia Ave. NW. Seven days a week, 24 hours (965-1717).

INTERNATIONAL HOUSE OF PANCAKES -- Call it early, early breakfast -- or late, late dinner. 935 North Stafford St. Arlington. Seven days a week, 24 hours. (522-3118).

KRAMERBOOKS AND AFTERWORDS CAFE -- Cafe society and lite reading. 1517 Connecticut Ave. NW. Weeknights till 1 a.m.; Friday and Saturday till 2 a.m. (387-1400).

LITTLE TAVERN -- A beacon in the night: the little white house with the little green roof and the little brown burgers (traditionally eaten in the car, in the dark). Various locations, all night.

MILLIE AND AL'S -- Collegial Adams Morgan atmosphere for pizza and Italian food. Weekdays till 2 a.m.; Friday and Saturday till 3 a.m. 2440 18th St. NW (387-8131).

OLD EBBITT GRILL -- Yuppie Heaven. This is where to take someone if you want to impress them with "typical Washington." 675 15th St. NW. Monday- Thursday and Sunday till 2 a.m.; Friday and Saturday till 3. 347-4800.

PERRY'S -- The stylish sushi isn't the only star here -- the muic and trendy crowd come a close second. 18th and Columbia Rd. NW. Weekdays till midnight; Friday and Saturday till 1 a.m. (234-6218).

RED SEA -- Authentic -- and spicy -- Ethiopian food, dubbed "African pizza" by some. 2463 18th St. NW. Daily till 2 a.m. 483-5000.

THE RUBY -- A Chinatown standby with a vast and mysterious menu. 609 H St. NW. Weekdays till 3 a.m.; Friday and Saturday till 4 a.m. (842-0060).

TASTEE DINER -- Four locations in Maryland and Virginia, all under different management; most important, all open seven days, 24 hours. 8516 Georgia Ave., Silver Spring (589-8171); 118 Washington Boulevard, Laurel (953-7657); 7731 Woodmont Ave., Bethesda (652-3970); 10536 Lee Highway, Fairfax (591-6720).

TRIO PIZZA AND SUBS -- Self-explanatory. 1624 Q St. NW. Weekdays till 2 a.m.; Friday and Saturday till 3 a.m. (232-5611).

TUNE INN -- The famous fun dive on the Hill describes its fare as "bar food." 3321/2 Pennsylvania Ave. NW. Weekdays till 2 a.m.; Friday and Saturday till 3 a.m. (543-2725).