Francesco Scavullo was on the phone when London designer Zandra Rhodes arrived at II Giardino for lunch Monday. Could he photograph Western singer Crystal Gayle in a Zandra dress, he wanted to know. (The answer was "yes".) Zandra was in Washington to plot her upcoming benefit for the Corcoran Gallery of Art in September. Zandra has been in New York for several weeks presenting her new coat designs which may be one of the best things that has happened to the coat business in a long time. In these designs, it's not Zandra Rhodes' typical fantasy, but her inventiveness that prevails. A variety of collars are among the distinctions - double collars, Z-shaped and pleated ones, yet all plain enough to be foils for jewelry. In the showings in New York recently, Zandra showed them with red satin face masks, a reminder of her trip to Peking. "But the masks also make a pretty color accessory," said Zandra, after seeing her designs on the runway.She may have given the coats their most worthy compliment - "They are coats I would really want to wear myself." She's made them for Sabrina Coats to retail from $200 to $300, "and that gives me a chance to reach another market I haven't had the chance to design for before," she said.

Most designers angled motion picture cameras on their models during recent runway shows of fall clothes in New York. Not an ego trip, the films are a sensible and useful record of the showing for those who missed it, those too far back to see it and store personnel who could not attend the show in the first place. Stores would do a service to show the films to customers as well.

So where hangs the hemline? After nearly six weeks of showings in Europe and New York, one thing is very clear - that your eye quickly gets used to a shorter proportion with the new slimmer clothes. Shorter means just below the knee, with a mid-heel shoe, 16 1/2 inches from the floor, 28 1/2 from waist. Many fashion editors were on Seventh Avenue last week with shopping bags of clothes to slip in a trip to the tailor for some shortening work between shows. Others had acomplished the deed before the shows began. In the better coat market, most styles for fall measure 47 to 48 inches from the back of the neck. But before you start attacking coats for a shorter hemline, remember that shortening a coat works only if you plan to shorten skirts as well.

Barry Iroff of Empire Cleaners has a plea for designers receiving accordion pleated skirts (and there are many.) Please make sure pleats are properly heat set, he urges. In a letter from the International Fabricare Institute commenting on the loss of pleats in such a skirt, they advised Iroff that pleat loss was "attributed to the inadequate heat setting of the pleats in the fabric."

It's theirs alone and no school can have one exactly like it since the T-shirt being given to Cardozo High School seniors on class night next Tuesday will have all the class members names on it. It is bound to become a big favorite at Cardozo to wear with designer jeans, currently the pet fashion, with high heels, for senior girls.

Bella Lynda. Lynda Bird Robb is wearing a new hat in more ways than one. She's taken over Bella Abzug's chair of the President's Advisory Committee for Women. Like her predecessor who always wears hats, Robb showed up for the reception in her own honor at the Vice President's house wearing a flower decorated shiny straw.

Fashion designers have been watching their television sets, particularly "Lillie Langtry." The high neckline, puffed sleeve, tiny waist styles at Oscar de la Renta and Harriet Winter were two good examples. De la Renta exaggerated the look using a red haired model with upswept hairdo that was a Francesca Annis look-alike.

Remember the big fur muff? The last time they were out in force was from about 1910 to WW I, when fitted suits were the mode of the day. So it's no surprise with the return of the fitted suit and coat that the muff is back, thanks to Calvin Klein and Bill Blass. (Klein showed a head-embroidered suede muff which you can bet they never saw back then.)

The only mystery is what you do with one. If the muff is meant to keep your hands warm it curtails walking with a comfortable stride as both arms cannot move freely at the side. If it is meant to carry things, don't count on it carrying much. And don't plan on carrying much else with it. We don't expect to see many in Washington. (Let's hope no menswear designer remembers that men carried muffs in the 17th to 19th centuries.)

Chadoors on Seventh Avenue? We knew it would happen one day soon and it did last week. Scott Barrie used head and body covering veils to conceal his bright colored spring outfits later revealed on the runway. Mary McFadden, whose show was delayed more than a half an hour while she made a last minute change in hairstyles, also used long chiffon scarves which gave the effect of veils.

A worthy distinction to learn for fall - the difference between sequins and bugle heads. For the glitz blitz on Seventh Aveune, both types of beading was used. The important distinction, bugle beads with tubular glass beads and usually hand appliqued and more expensive. Sequins are flat plastic and metal disks attached like buttons. Sometimes the fabric is bought already sequinned and the garment simply cut from the fabric; sequins, however, also can be hand embroidered into specific patterns. Among those opting for bugle beads in New York collections for fall: Calvin Klein, John Anthony, Ralph Lauren. In the sequins camp: Oscar de la Renta, Halston, Kasper and many others.

It's not only silks and satins that are getting guissied up - but suede too. Calvin Klein studs his suede too.Calvin Klein studs his suede with bronze, for a subtle but dressier look.