Trio 1537 17th St. NW. 232-6305.

Hours: Open daily from 7:30 a.m. until midnight.

Price range: Sandwiches from 80 cents. Complete dinners to $5.85.

Reservations: No.

Credit cards: American Express, Carte Blanche, MasterCard and Visa.

Special facilities: Booster seats; highchairs; double-doors entrance.

Close to the downtown business area is a restaurant reminiscent of a diner, a cafeteria and a favorite college haunt. All the standard characters from a Jack Nicholson movie are in place at the Trio. The regulars take up residence and linger over coffee, while the uninitiated get the Trio treatment.

Prices match personality. The Trio has few modern amenities and seems never to have heard the word "inflation." That's no doubt why it has a loyal following. Its prices compete with home-cooking costs.

Yet, what do you get for the 1950s style? Certainly not an appealing decor. What you have is a no-nonsense establishment with a large menu and daily dinner additions that emphasize food in season.

Seconds after we had selected a booth, the waitress was eager to take our order. We weren't ready to decide, however, and she looked hurt. More time elapsed, and we were still debating selections. The hurt look became a scowl.

When we finally were ready to order, she pounced. Of a crab cake choice, she said, "No crab cakes."

The day's temperatures must have simmered our brain cells as we continued down a woebegone path and ordered jumbo shrimp stuffed with crabmeat. The following dialogue ensued:

"No."

"You mean, no shrimp?"

"No. No crabmeat. I told you, no crabmeat."

She won. My husband ordered a sandwich.

Somehow the conversation was part of the Trio mystique. As with the decor, it had little to do with the final evaluation and, if anything, it livened up our dinner conversation.

The difference between many of the items on the regular menu and the dinner choices for the evening is that dinner includes soup, two vegetables and a drink. What the waitress lovingly called a la carte included rolls, salad and fries. It sounded more than sufficient and, anyway, turkey barley soup attracted few enthusiasts in our family.

Everything happens at the Trio immediately. Seconds had barely elapsed before three large dinner rolls with individual butter pads appeared. Right away you understand the restaurant's concern for feeding you well. These are the type of rolls mothers fret over. They're huge!

Salads follow within minutes. Not a fancy bowl, but a crisp portion of greens topped with tomato slices. Just right.

Each selection was successful. A large slice of medium roast beef ($4.30) was well trimmed of fat. A platter of jumbo fried shrimp had been delicately breaded and quickly fried. Liver and onions ($3.30) were moist and free of steam-table blues.

Even the turkey club demonstrated value -- no imitation turkey roll, but rather slices of the real bird piled into a triple-decker creation.

Amid the food fanfare, we somehow received another waitress. Maybe we had earned her. She quickly cleared our plates and asked if we wanted dessert.

Since none of the pies was homemade, we figured it was time to return to the 1980s and see what fruits were still available at the Saturday stand across the street.

The Trio gives you rock-bottom prices and food that reminds the mature eater of restaurants that once filled a reliable role in an earlier period. It's a time warp right on the busy corner of 17th and Q.

Dinner for four with tax and tip amounted to $22.77. At those prices, no wonder it's a busy restaurant.