It's all over but the buying, and generally the fall clothes to come, shown over the past few weeks in New York by Seventh Avenue designer "names" can be summed up as looser and roomier, a greater mix of fabrics and more expensive. What will be around this fall that wasn't in sight the same season a year earlier include: the big blousons, the storm coats, printed wool challis and shearling. For daytime the mood is decidedly casual with pushed up sleeves, turned up collars, loose tops that virtually slip off the shoulders, thick hose and flat shoes.

The big winners on Seventh Avenue: Stephen Burrows for his deceptively simple sweater dresses, chiffon and matte jersey: Halston's long-johns used as a modern way of layering under evening dresses as well as well as daytime clothes: "Geoffrey Beene's unexpected fabric mix in the best loosened up clothes around; Calvin Klein's totally gimmickless separates mixing velvet, linen, flannel and crepe de chine; Ralph Lauren's man-sized jackets with slightly pegged pants; Bill Blass' quilted jackets and plaid separates for Blassport; and Gil Ambez's great big dresses.

There were ideas that didn't work: quilted shorts, black tennis gear, sweaters worn over men's jackets or (try this), two sport coats worn together.

Designers often overdosed on gold. The way it works best is as Bill Blass did it - a gold blazer or sweatshirt paired with gray flannel trousers or skirt. A touch of trash, you might say.

Good accessories not to miss: thick, often ribbed and usually very casual tights; flat shoes modeled after navy officer's style or ballet slippers; tuxedo shirts with tiny front pleats; a curling iron to make your hair frizzy; a big shawl in challis for one last layer of warmth. For the men, glove tucked in the hankerchief pocket a la early Duke of Windsor, with fingers up, please.

Yves Saint Laurent again wins the prize of giving out the most ideas translated by American designers. Pierrot collars, challis, zoave pants, the little girl ruffled dresses kept reappearing in many collections taken on as the idea of that designer.

The fall fashion collections were a week earlier this year than last, in order to get earliest possible orders on fabric for the mills. "Mills are demanding more time to make their deliveries and so we need buyers' orders in earlier," explained Jean Pierre Radley at Pauline Trigere. Pam Miller at Saks Fifth Avenue says it will also help getting fall clothes in to the stores earlier in the summer. "When clothes have gotten so expensive women want to wear them as long as possible. Even in Washington, some of the lightweight cashmeres and the silk crepe de chine are suitable for summer," she says.

One New York store isn't even waiting until summer to talk about fall clothes - Bergdorf Goodman ran a full page ad recently to introduce some fall styles.

Amy Carter is the first on her block to start a fall wardrobe. It's part of the purchases made for her by mother Rosalynn Carter and sister-in-laws Judy Carter at The Little Folks Shop in Calhoun, Ga. Selections ranged from jeans (which Amy wears to family dinners) to one-of-a-kind designer samples from Dorree Selvan of Dorissa of Miami, some suitable for state dinners. Amy expressed a penchant for peasant styles and any color but pink. Total tab for all of Amy's summer and fall purchases-about $750. "Mrs. Carter told me it's been impossible to shop in Washington, and that even shopping in Americus, Ga., has become impossible," said Linda Dillard, the children's wear shop owner.

Among those snapping the bodysuits and chiffons at Halston was the photographer from the News World, the newspaper of the Moonies.

A sure sign the flower fashion accessory is going to happen this summer - unlicensed vendors were out on Madison Avenue this week doing a landoffice business on fabric flowers with as much variety as the Burpee Catalog.

The real big jewels that have been hidden away for years in New York vaults were taken out and dusted off for the recent Frank Sinatra benefit. Barbara Sinatra led the pack with her sapphires. For Jackie Onassis it was long diamond drop earrings. She also wore long white gloves which some fashion types hope will do for the glove business what her pillbox hat once did for milliners.

One signature of the Paris fashion trendies that has started to show up in New York is wearing socks with sandals and espadrilles.It is not such a dumb idea since it makes sandals wearable almost year round.