Atmosphere: Tasteful, comfortable Mexican decor; dress can be casual.

Hours: Monday through Saturday, 11:30 a.m. to 10 p.m.; Sunday, 4 to 10 p.m.

Price Range: $4.45 to $6.75; children's dinners $2.15 to $2.50, complete.

Reservations: Not necessary, but they can be made.

Credit Cards: American Express, MasterCard, Visa.

Special facilities: Accessible to wheelchairs; highchairs and boosters available; easy parking in lot adjacent to restaurant.

It remains to be seen if an influx of Reaganites will transform Washington into California-on-the-Potomac, but one thing seems certain. Californians will find enough Mexican restaurants in Washington to make them feel at home. w

Viva's located south of the border near Little River Turnpike in Annandale, is one of these. While you can get better Mexican food at other places in town, it is hard to beat the total package Viva offers: decent food, a charming ambience, and good service at surprisingly reasonable prices.

We were only one of several families at Viva's on a recent dingy Sunday night; the brightly decorated interior was inviting after the dismal December weather. Multi-colored serapes and Mexican artifacts hang on the stucco walls; pierced tin hanging lamps provide soft but adequate lighting, and a lovely collection of Mexican pottery dominates the central section of the dining room. We were seated in an alcove to the left, where a series of booths lend a sense of coziness.

Our waiter, one of the most solicitous we have ever encountered, appeared with two baskets of warm tortilla chips and bowls of salsa piquante. The menu offers various combination plates, which can be ordered either a la carte or as a complete dinner -- that is, with either soup or guacamole salad added to the platter. All are well priced at around $5.

But the real buy is the menu for children under 10. For $2.50 and under, kids can order a plate of two tacos, or two enchiladas, a combination plate or a plain old American hamburger, with a drink and ice cream dessert included.

Our younger daughters ordered cheese enchiladas, $2.25, without a minute's hesitation, and our older daughter decided on an a la carte plate of three tacos, $4.95, including either rice or refried beans. My husband and I were curious about the house specialties, and so ordered chicken chalupas, $4.95, and the Mexican flag plate, $5.50, which was essentially a dish of beef, chicken and cheese enchiladas, one covered with sour cream, one with red sauce, and one with green, duplicating the tri-colors of the tiny Mexican flag which topped the platter when it was served.

The girls were happy with their enchiladas; my husband found his dinner unexciting but decent fare, and the same could be said of the chicken chalupas. The dish was served in a shallow bowl and the ingredients layered: first, fried masa dough, then bite-sized pieces of chicken coated with a piquant sauce, then shredded lettuce and cheese, and a garnish of tomatoes, avocado, chilis and sour cream. I would have preferred less lettuce and more cheese, but the dish was hearty and tasty.

Ingredients in the tacos were fresh, but seemingly unseasoned ground beef made for a dull taco, even if the flavor with which you are familiar comes out of a foil packet from the supermarket. A little hot sauce from the bowl on the table and a bit more shredded cheese would have improved them. We don't like our Mexican food to be fiery, but it should have flavor. t

At dessert time, we were all disappointed to find Viva's kitchen was out of sopapillas, fried dough served with drizzled honey. We settled for orange sherbert and a snowball, the classic vanilla ice cream ball in coconut served with chocolate sauce. Each was 75 cents.

The real treat, however, came with the bill. Five of us had a pleasant, full course dinner, complete with one glass of sangria, in lovely surroundings for $29.99, including taxes and tip. And that's worth saying "Viva!" about.