MARY Ellisor Emmerling and her husband John Emmerling were recently divorced. Her new apartment is Country style. His is High Tech.

"My fondness for Country was one of the reasons for the divorce," admits Emmerling. (Her new book, "American Country, a Style and Source Book," has just been published by Clarkson N. Potter, Inc.)

They may not be the only couple to split over two opposing styles of decoration.

This summer manufacturers, shops, books and magazines are sending this message for people decorating houses or 30th-floor apartments:

Throw out your metal racks, your filing cabinets, sideboards and your moving-man bedspreads. Down with High Tech, up with Country style.

Country style is soft not hard, romantic not classical, old not new, rough not slick, innocent not sophisticated, funny not clever, dainty not strong, ruffles not flourishes, artless not artifice, casual not formal.

Country is not confied to Early American. Country isn't even necessarily antique, nor limited to a specific time. It can be brand new, but it should have that rough-edge quality about it that says it doesn't come straight from the assembly line.

Country colors are a principal ingredient in the look. They have a good admixture of gray in them. That's different from pastels, which are mixed with white; or primary colors, which are pure, intense colors. The graying gives everything an old, antiquey look that some people find comforting and familiar.

In furniture, oak, pine and the fruitwoods are right. They should be used without a slick, highly polished finish. The well-scrubbed matte look is right. Painted furniture is another option -- especially if you're good at stencilling.

For real antiques, look for farm furniture, or oak chests, tables and chairs from the arts-and-crafts movement around the turn of the century, persisting to the 1920s, sometimes called "Mission." These pieces are already being collected and will be worth a lot some day.

Much good Country furniture is still being made by craftspeople. The fairs are full of good Country ladder-back chairs, for instance. And you can even find Country furniture on sale sometimes on the sidewalks of Washington. e

Fabrics are the quickest way to put together a Country look. Look for calicos -- small prints, often floral -- or ginghams -- on white or grayed colors. Ruffles, smocking, embroidery, gathers -- everything goes. In solid colors, look for canvas, homespun, rough fabrics that have a handmade look.

The fabrics are often used on walls, either stretched and stapled or simply shirred or hung like curtains. Many manufacturers are making matching wallcoverings to go with the fabrics. A cheaper and authentic way to go is to paint the walls a solid color and stencil a design.

Pottery, of course, is just right for the Country look. You can use a mixture of designs, and not be ashamed. The best route is to go to a potter with a big production kiln like Trew and Tony Bennett, Buck's Creek Pottery, Faber, Va., and have a complete set made especially for you.

On the grandest scale, Rosalynn Carter had American potters and glassblowers make 12 sets for her luncheon for Congressional wives her first year in the White House. One Christmas, she had American handmade decorations for the tree. Mrs. Mondale has ordered a permanent set of pottery for the vice president's residence, along with her Sam Maloof rocking chair and other crafts, some Country, some contemporary.

In the 1980s, Country style is a natural reaction to the industrial look, which emphasized function over form -- or, in some cases, the look of function. There are some other reasons: the Bicentennial, the crafts revival, the Smithsonian's folk-life festival, the Jimmy and Rosalynn Carter White House, Joan Mondale's craft interests, blue jeans, country music and more casual, relaxed way of life.

Though the Bicentennial certainly aroused interest in Americana, the current Country theme started in the mid-'60s with the craft revival in the United States. People talked about dropping out of the rat race and heading for the hills; living the simple life and living off the land; making it yourself and making do. From this attitude grew a country-wide interests in crafts not only as a career but a way of life. Schools, colleges and private teachers sprang up to instruct these interests. And now, shops and craft fairs are opening to sell the wares.

The Smithsonian's Folklife Festival, beginning in 1967, was a big impetus to an appreciation of Country.

Ralph Rinzler, a founder of the festival who went all over the country collecting crafts for the early ones, once owned a shop called Country Roads in Cambridge, Mass. Rinzler still has one of the best Country-style houses in the city of Washington, filled with a great collection of Country crafts.

"When I visit houses around town, I still see crafts I collected in the '60s for the festival," he said.

Good news: The Smithsonian Folk Life Festival, this year Oct. 8-13, will go back to its prime time of around the Fourth of July next year.

The Baltimore Winter Craft Market is currently the biggest assemblage of crafts for sale in this area. The event is scheduled next year for Feb. 19-22.

In the '60s, quilts were the first to be collected and displayed. Pottery was next. But then folk art of all varieties, from paintings to weathervanes became popular. After that, people began to look for bits and pieces of Country furniture -- prizes such as the shoo-fly chair with its pedal that worked the horse's tail, and more ordinary but useful pieces such as trestle tables.

Country decorating is thought of as cheap, not costly. It's true enough if you contrast the price of calico and velvet. It's false if you're talking about good Country antiques.

Today, prices on Americana are way, way up. Bernice Chrysler and Edgar William Garbisch, who died Dec. 14, were the pioneering collectors in our time. Their "Naive," as they liked to call it, painting collection has been given to the National Gallery of Art. But their furniture, rugs, needlework, pewter, and copper cooking utensils were sold off recently by Sotheby Parke Bernet at the Garbisch Eastern Shore home called "Pokety." The largest Americana auction anywhere broke all records for an American on-the-site sale with a total of $3,903,530. A hooked rug sold for $12,000, a small paper trinket box brought $7,250.

Of course, many people who prefer Country are like Mary Ellisor Emmerling. She likes Country, not just because her former husband doesn't, but because: "Days when I was sick of the city, I would walk into the apartment, smell the popourri, warm myself at the fire, admire my twiggery and feel warm and relaxed and comforted. I think today especially with the Iranian situation, the world is confused. American Country is a warm, cozy look.

"I started collecting Country about 10 years ago. My ex-husband was into flying. So while he was up, I would poke about in the aucitons in Vermont.

"I'm not good at saving money, but I found I could buy things in the small shops and flea markets and get bargains. I made money reselling them. I was working for Mademoiselle then, and the editor thought Country style was just right for the young readers of the magazine. So we used our apartment a good bit to shoot features." The apartment Emmerling shared with her former husband and two children also has been published in House & Garden and House Beautiful.

Emmerling thinks her major contribution to the development of the style was to put Country furniture and accessories against white, white walls. "The reason people hadn't liked the Country before," she said in a telephone interview, "was they had seen it in New England houses, with little windows, dark walls, small rooms. I went west and photographed it there."

It isn't necessary to put Country style in big spaces, Emmerling thinks, though she longs for a big, open loft. Her new apartment is quite a bit smaller than the one she shared with her former husband and the children. Her brother looked at the fire place, her four-poster bed and her other Country prizes and said, "It looks like you put your old apartment in the washer and it shrunk."

Emmerling is so in love with Country that she says, "our children [3 1/2 and 6 1/2] never have store-bought toys. They love handmade things."

Even though a great many companies are making reproduction Country furniture,, Emmerling doesn't think anyone does it well. "It's all too shiny," she says. She does include in her decoration contemporary sofas and chairs. "I got tired of people looking uncomfortable in my house."

Clutter is the big thing to avoid when decorating Country style, said Emmerling. "All those bitsy patterrns can get" tiresome if you have too much of it. I like to mix in a good helping of solid canvas."

Emmerling herself grew up in Georgetown. She is the great, great, great granddaughter of President William Harrison.

"I think Washington, Georgetown rowhouses and the Smithsonian were big influences on me." Her mother, Marthena Ellisor, still lives in Washington.

Now Emmerling is decorating editor of House Beautiful. Three weeks ago, she opened a shop in South Hampton, Long Island, called "The American Country Store." In her book, she has a 40-page directory for Country objects, both manufacturers, museums, and shops. The photographs of a 200-year-old barn owned by William C. Musham and his wife Bettye Martin in Bucks County, Pa., are by far the most interesting part of the book.

The barn was designed by Raymond Waites and the Gear Team with furnishings and fabrics they are now marketing. Waites is also the designer of "American Country." The foreword by Dr. Robert Bishop is informative. As seems to be the pattern these days, the book was produced by a team including a text by Elizabeth Warren.

"Decorating Country-Style -- The Look and How to Have It" is by Patricia Hart McMillian and Rose Bennett Gilbert, formerly with 1,001 Decorating Ideas, and authors of "The You-Do-It Book of Early American Decorating" (Doubleday). The book is full of information as well as pictures. Simplified instructions are given on such useful handcrafts as stencilling, spatter painting, texture paints, and so on. If you are seriously considering leaving for the country, this book is a good guide, as in their early book.

Going down the country road might well give you a chill when you think about France in the 1780s. Remember all thoe aristocrats who played milkmaid, said "let them eat cake," and sat on chairs made to look like trees, in rooms made to look like bowers, while the world fell in around them. Enjoy your country comforts, but don't stray too far from today.