One night spent at the St. Regis Sheraton Hotel in New York turned me into a fast-food fan. It's the room service that did it.

The St. Regis' charge of $11.75 for continental breakfast astonished me, and that is before adding the $2 room-service charge, the tax and the tip. A hamburger is $12.25 (with cheese and bacon, but again those charges would add another $4 or so to it).

Room service prices are not as bad elsewhere in the country. At the Fairmont in San Francisco, continental breakfast is $8 (plus service, tax and tip), a hamburger the same price. Atlanta's Ritz-Carlton is slightly lower, $7 for the continental breakfast and $7.75 for a hamburger. Washington's splashy downtown J.W. Marriott charges $6.26 for the continental breakfast and $7.95 for a hamburger, with french fries.

And while one would expect no place to be more expensive than Dallas' Mansion on Turtle Creek, putting together a continental breakfast from its a la carte menu would add up to around $8, and its hamburger is $9.75. Even though less than New York's, such prices are disagreeable, to say the least.

Hotels have all kinds of excuses for these stratospheric amounts: round-the-clock staffing, individual service, special equipment needs. None of them explains the phenomenon.

And the Days Inn motel chain has made those excuses seem even more hollow. At three of Days Inn's motels, in Atlanta and Greensboro, N.C., Wendy's is doing the room service. As is usual with room service, orders can be placed by phone, charges can be added to the room bill, and service is within minutes of ordering. The Days Inn service is not around the clock, but that, says Wendy's, is because there has been no demand for lunch or late-night service.

At these Days Inns the equivalent of a continental breakfast costs about $2, or maybe $3 if you add egg, cheese and bacon to your english muffin. A hamburger costs $1.45 to $2.75, depending on the size. A 20-percent room-service charge is added to the bill; but no tipping is allowed. The only complaint I have heard about Wendy's room service was that with a minimum of $2.50, it was hard for the motel guest to find enough on the menu to add up to the minimum.

Okay, there is the quality question. Wendy's breakfast isn't the St. Regis breakfast. But if what you want is a reliable cup of coffee, served promptly when you want it, that is no more available at the high end of the price scale than at the low.

Tabletalk The refrigerated-meal competition in grocery stores is heating up. The newest entry I have found is Tonight's Choice -- separately packaged meal components -- from Emmber Brands in Milwaukee, which is planning full national distribution within the next several months. A sample I tried was pretty good. Butter-sauced sugar snap peas were still crisp after shipping, a day in my home freezer and microwaving; my only complaint was the butter sauce was sweet. Grilled chicken breast was moist and smoky, as well as attractively browned and fresh tasting. Rice casserole was gummy and overseasoned, and pie was dreary. In all, though, the appearance of Tonight's Choice is promising news.

Chinese food and California cuisine will take a back seat in San Francisco on Sept. 13 when Mexican cooking has its day. The event is "Feria de la Bahi'a: A Taste of Mexico," at Pier II, Fort Mason, from 11 a.m. to 5 p.m. This 5,500-square-foot indoor pier will become a Mexican marketplace for the day, with local restaurants and food vendors selling foods from eight regions of Mexico, and with a bow to West Coast and Southwestern cooking that has been influenced by it. In addition to the sampling, the fair will include cooking demonstrations, and strolling musicians. Admission is $5. For more information call (415) 441-0445.

An appropriate prelude to a Mexican food festival is the first ever California Dry Bean Festival, in Tracy, Calif., Aug. 22 and 23. The organizers tout it as the biggest bean extravaganza from Boston to Banta, which wouldn't be a hard claim to defend. In any case, there will be the opportunity to taste chili beans, creole beans and international bean dishes from Basque Sheep Camp Beans to Lima Beans Con Chili Con Queso. For more information call (209) 943-7684.

Every couple of years Ocean Spray Cranberries, Inc., brings together food writers and potential newsmakers for an innovations seminar -- lubricated, of course, with cranberry drinks and garnished with cranberry accents. This year the culinary hit, though, had nothing to do with cranberries; it was an extraordinary -- and simple -- preparation of baked clams by Al Forno restaurant of Providence, R.I. Here is the recipe:

CLAMS AL FORNO (4 appetizer or 2 main-course servings)

24 littleneck clams, scrubbed

1 medium onion, halved and sliced thinly

1 jalapenåo pepper, coarsely chopped

1/4 teaspoon or more red pepper flakes

1/2 cup dry white wine

1/4 cup water

1 tablespoon minced fresh garlic

1 cup drained canned Italian plum tomatoes, chopped

Chopped parsley or sliced scallions for garnish

In a baking dish combine all ingredients except parsley and scallions. Bake at 500 degrees for 5 to 7 minutes, until they open. Turn clams. Discard any unopened clams.

To serve, place 6 clams in each of 4 bowls. Surround clams with tomatoes and onions. Divide liquid among the 4 bowls. Garnish as desired with parsley or scallions.

1987, Washington Post Writers Group