The popularity of Phineas II in Springfield is testimony to the Marriott Corporation's knack for marketing food.

Marriott, already established as one of the major provides of Washingtonians' fast food - Roy Rogers, Hot Shoppes, Fairfield Inns - now has dinner houses. The houses, like Phineas II, are the new palaces of fast food. They are designed for the family who likes a little atmosphere with its meat and potatoes. The price of a dinner, usually about $8, includes enough frills like salad, breads and wine to justify the step up in style.

The menus are limited, primarily steaks, prime ribs and lobster. The food is prepared by high school students working off laminated recipe cards to assure consistency in quality, according to Phil Davis, manager of Phineas II.

The chefless dinner houses have become so popular and have turned into such moneymakers for Marriott, Davis said, that the corporation has opened 14 of them in the past few years.

On a recent visit to Phines II, just west of I-95 off the Springfield exit, I escorted my 13-year-old brother, who was visiting, and my 2-year-old son. Since the restaurant has at times as long as an hour's wait to be seated, we went early, about 5:30 p.m. We were seated immediately.

It was apparent that some care had been taken with the decor: The dining room is sectioned off into intimate areas, dimly lit by brass lanterns on the table. The tables are handsomely set with water and wine goblets, heavy silverware and pewter ash-trays.

Our waitress, a pleasant young woman named Mary Ann, appeared promptly with menus, a carafe of burgundy for me and fruit punches for the boys, all included in the price of the dinners.

My brother Michael ordered the small portion of prime rib for $6.45; I chose the larger cut, which was a dollar more. There also were several variations of beef or lobster on the menu with the top price for a dinner at $8.95.

While we waited for our selections we visited the salad bar. There was the usual array of vegetables and dressings, and a large wooden bowl of Caesar's salad, with crisp romaine lettuce and croutons coated with a flavorful dressing very close to what it should be. Also available was a good, heavy white bread.

As soon as we had finished our salads, our dinner was served. The prime rib was juicy and tender, and cooked to our specifications. Accompanying it were hot popovers and a side order of pan-browned potatoes for 50 cents. Both were quite good. A nice whipped horseradish dressing is also offered as a garnish for the meat.

Also available are side orders of spinach casserole, 85 cents, and mushroom topaz, $1. A children's menu includes smaller portions of beef or lobster, for $2.95 or $3.50.

The deserts, chocolate cheese cake and old English trifle, both $1, were the only disappointment of the meal, but the coffee, served in an ornate silver pot that is left at the table, was freshly brewed.

While we waited for our check, my brother, who can be a fussy eater, informed the management on a card provided for customer comments that he found the dinner "excellent." Our entire bill, excluding tip, was $17.59.

Boosters and high chairs are provided.

Phines II, 6900 Old Keene Mill Road, Springfield, 451-7884. Mastercharge, BankAmericard, Diners Club, American Express. No reservations. Open 5-10:30 p.m. Monday through Thursday, 5-11 p.m. Friday and Saturday, noon to 9:30 p.m. Sunday. Accessible to people in wheelchairs.