KNITTING MACHINES, still relatively unfamiliar in the United States, are basic equipment for housewives in most other parts of the world. In Argentina, more knitting machines are sold than sewing machines. In Japan, the knitting machine is as common as a toaster or pillowcases in a bride's trousseau.

The idea is beginning to be familiar here at last -- perhaps because the products of the knitting machine are becoming so widely known -- not only those that bear the Adolfo label but also the custom clothing produced by many less prominent designers.

The National Knitting Machine Seminar held recently at the Sheraton National Hotel in Arlington seemed planned for about 250 participants, but actually attracted about twice that number. Many of the workshops -- particularly those dealing with practical use of the knitting machine -- were sold out almost as soon as they were announced. It took a bit longer to fill the workshops on knitting machines as a medium for artists, but they were also well attended.

Knitters are at two levels: the trendy professionals, who design clothes or make textile art and use the knitting machine as another tool; and the home knitters, people who used to knit by hand for their family and friends and have taken on the machine to help them.

The work of Susanna E. Lewis of New York, a professional designer, is displayed in many museums and galleries. Like many members of what is still the first generation of machine knitters in America, she is primarily self-taught. She was already a fiber artist in several media in 1971 when, she says, "I decided I wanted to settle into one technique; I wanted to create fabric."

She happened to pass by a knitting machine store, wandered in and began an acquaintance which did not really become productive until 1975. "It took me four years to get started," she says. "I just went through the owner's manual very methodically; almost everything I know and teach is in the owner's manual. You just have to go through it very carefully and think about its implications and possible variations.At the end of four years, I could do just about anything I wanted."

Lewis, a former biologist and musician, is also a student of folk art, which influences her own production in the fields of wearable art and architectural hangings. She currently is working on two books, one on advanced techniques in machine knit fabrics and one on hand-knitted lace, and she teaches advanced machine knitting techniques at the Parsons School of Design in New York. "My self-concept is as an artist," she says, "and I use the knitting machine as a tool in creating art."

Gene Bailey of Philadelphia, one of the growing number of male machine knitters, treats the knitting machine as a tool for designing and making clothes that he can sell to such outlets as Bloomingdale's and Bendel's.Before he began knitting, about six years ago, the young designer had no experience in knitting or designing. Now he drafts his own patterns (favoring classic and conservative styles) and creates his own knits with unusually intricate combinations of stitches.

Like the art and fashion knitters, many of the home knitters began with a sense of puzzlement at the strange, formidable machines that they meet more or less by accident. Helga Andrews, from Cookeville, Tenn., a hand knitter, owned two yarn shops when she first encountered the machine through one of its products.

"A friend of mine brought in a sweater," she recalls. "She was wearing this top and it interested me, so I became interested in the machines. I bought one from a distributor who did not know how to use it and could not teach me. I tried to teach myself and couldn't, so I just put it under my bed and I cried because I had paid all that money and I couldn't use it at all.

"About a year later a friend called and said there was a seminar in the Washington area -- the very first one -- and we went. When I saw all those clothes, I knew there was a market out there. So I inquired at the seminar and found a woman who would give private lessons. I went to see her on Sunday and stayed all week, and by the time I left I had made four sweaters."

Originally she did most of her machine knitting for her three children, but now she is beginning to knit skirts. Her yarn shop is a natural point of contact with customers. "They come in for yarn to make a sweater," she says, "and I offer to knit a skirt to match the sweater."

Carol Maroglio learned about knitting machines from her mother, whose sister had used one for 20 years in England. "I wasn't interested in hand knitting," she says. "I thought it was kind of silly, but once I saw all the things you could do on a machine, I became really excited."

She still remembers her first sweater: "Some days, I wondered if the yarn was going to fall apart before I could finish. But I wanted to be creative, and so I kept on. I like the machine because it goes so quickly. I like to see results, the way I can in sewing. When you're sewing, the results show up right away."

Sara Brooks, who operates The Knitting Machine Shop, tucked away behind Atherton's Book Shop in Kensington, Md., is one of the few professional teachers of knitting machine techniques in the Washington area. "By the time my students finish the beginner's course," she says, "they have made at least two sweaters and planned a third. I cover more careful fitting in the intermediate course. When they have finished the eight lessons, they are capable of knitting a tailored suit. Most of them become so enthusiastic that they keep coming back for specialized workshops."

Quite a few husbands take the courses with their wives. Knitting is no longer considered a masculine occupation, but knitting with a machine seems to interes them.

Corky Haase, a co-proprietor of the Art in Fiber Gallery at the Watergate, finds that "Americans are excited by usable technology." She has owned one knitting machine for two years (a bulky machine, which uses thicker yarn and looks less complicated and threatening than more advanced machines), and has just bought a new one -- a Superba, made in Switzerland, which can "read" patterns electronically and make the right needle settings automatically. Like many machine knitters, she particularly likes the speed with which she can begin to see results. And the flexibility. "When you say 'machine,'" she says, "you think of something rigid and standarized, but the knitting machine allows you to be individual and creative."

Some of the individuality and creativity unleashed by the knitting machine was on display in a recent show at her gallery. There was a knit silk kimono whose color shifted gradually form an ethereal yellow at one end of the fabric to a delicate green at the other, in stages so subtle that no breaks in the smooth flow of color could be perceived. A burgundy chenille knit evening gown, with an attached shawl as intricate and light as a cobweb, a full-length coat in lavender and cream paisley, whose lining (reversing the outside colors) was as beautiful as the exterior.