THE PICTURES are diffused, or in photo lingo, soft focus, but the message is clearly sexy, sometimes erotic, in the new Bloomingdale's lingerie catalog called "Intimacies." No less intimate then its predecessor, which had controversial slice-of-life photographs by Guy Bourdin, this time the models, always women, are stretched out on satin sheets, sitting in seductive poses or taking provocative stances. The photographer is David Hamilton who is admired for his photographs of women, particularly dancers.

Arthur Cohen of Bloomindale's had seen two of Hamilton's books - he's not sure which ones - felt "his photographs were appropriate for the shift of the mood of fashion to something softer," he said.

This time around, cosmetics are included, a way to save money on increasing postal costs, says Cohen, by combining two separate books. Manufacturers displayed in the book contribute to the cost, which Cohen says runs between 25 cents and 75 cents per issue. The catalog is not a moneymaker, except perhaps for the bookstore that was selling last year's copy for $12 shortly after it was a declared a "sellout" at Bloomingdale's.

"Not so raunchy as a year ago," comments one viewer about the new catalog. "In fact, in comparison, it is almost good taste."

Britches of Georgetown is going back into the women's clothing business. David Pensky, co-owner and founder and founder of the business, would not confirm it but did say he would be going to Paris to look the ready-to-wear collection this fall.

Pensky, just back form the menswear show in Paris, says the magic word for next season is "decontracte" - relaxed, wrinkled, easy, unstiff clothing in muted colors, always shown in textured natural fabrics. He likes the look very much and thinks that it is the new direction for women's wear as well. Chances are the "decontracte" look will be featured in the new men's/women's shop, likely to be located on lower Wisconsin Avenue where the Britches sale shop is now. Britches was in the ladies clothing business once before with early Ralph Lauren designs. The women's clothes never made it, bogged down by limited selection and bad deliveries, Pensky said.

True innovation, not to be confused with mere faddishness, deserve highlighting when it shows up as it did in the recent Bill Atkinson collection in New York. Atkinson has designed a skirt with a Peter Pan collar at the waistline that can be worn as a stand-up collar if you prefer the wider waist-band. A sash tie takes on the look of a man's tie, but a real tie would work as well.

Joan Mondale caught up with one of her favorite designers, Joan Sibley, in the dressing room of Saks/Jandel this week. Sibley (who has dissolved her relationship with Dory Coffee) keeps her collection limited to a number of strong pieces that can be worn in lots of different ways. Like the ruffled blouse (pictured) that can be teamed with a challis skirt, or worn for evening with jersey pants.

Several of Sibley's costumes are ankle length ("It's never than pajamas and besides, shoes are so pretty this year"), including the dress Sibley wore to a party on Monday for Valentino, the Italian designer.Sibley calls the style her "good posture dress" because of the decolletage. Count on Mrs. Laughlin Phillips and Val Cook to have good posture - they bought the same dress.

A witty view of the faces behind some of the most important labels, particularly of the 1940s when designer labels were first sewn into garments, is presented in the current collection of caricatures by Aline Fruhauf at the Corcoran Gallery of Art. Valentino, Tom Brigance, Lily Dache, Clare potter, Nettie Rosenstein and Sally Victor are among the many designers Fruhauf captured in what Jacob Kainen calls intensified portraits. "I would make endless sketches until one seemed to talk back to me," says Fruhauf, whose works have been published in Vanity Fair, Theater Arts and Esquire, as well as newspapers. She could recall only one, Respighi, where she never really "got" the person to her own satisfaction.

Other Fruhauf caricatures in the exhibition are Thomas Hart Benton, Jascha Heifetz, Katherine Cornell, Clarence Dorrow, and Martha Graham. Fruhauf has done portraits of Charles Dawes and Nicholas Longworth, "but politicians don't interest me, really," she said. "I'm just more attracted to creative people. I guess you could say I'm a snob."

Fran Frazier is one of those women who cannot bear to throw anything away, particularly if it has costume possibilities usable in her role as wardrobe mistress for the Pierce hall Players, an amateur theater group at All Souls Unitarian Church. But now she's ready to let go of some of the '30s, '40s and '50s things. If you dream of looking like Jean Harlow or Lana Turner, of really do, the appropriate dresses are available, plus four carloads more. Other finds - some old-fashioned pearls and some men's black tuxedos. The sale will be from 10 a.m. to 4 p.m. Oct. 1 and 2 and 702 Bonifant St., Silver Spring.

We dropped a stitch in our sewing class list. Sew and Sew Forth in Springfield mall (971-9400) offers classes seven days a week, including basic and advanced sewing, speed sewing, menswear, lingerie and swimwear, which are all taught on their machines. Fees are $15 to $39.95 for eight or nine-week courses. Also, Sewing World in Bethesda (530-7550) offers eight-week classes for $30 in basic skills as well as tailoring, sewing for children, knits and machine embroidery.