Some menswear designers tag their new look a throwback to the 1930s and 1950s. Others say it comes from the avant-garde of Japan and London. But no matter how you date it or where you place it, the effect is the same: Men's clothes are being inflated by roomy jackets, baggy pants and full-cut coats.

"The essential thing is that clothes be comfortable," insists designer Randy Allen, whose square-cut, easy-fit clothes are becoming increasingly popular in Washington.

Allen was wearing a white cotton anorak and black cotton beach pants and sneakers as he talked to customers earlier this week in a hotel room-turned-showroom filled with racks of his summer designs. He was one of almost 60 American and foreign menswear designers, members of a nonprofit group called the Designers Collective, who took over five floors of the Berkshire Place Hotel here to peddle their clothes to wear when the hot weather returns. Among those showing their lines were several stores, such as Brown's of London and Hammel's of Zurich, so successful with avant-garde clothing they have gone into the wholesale business.

Many designers stood outside their makeshift selling areas to chat with competitors and at the same time lure some of the 2,700 retailers attending the show to their often unfamiliar labels. Exhibitors included several makers of traditional clothes such as Alan Flusser and Jeffrey Banks, as well as small, trendy companies from England, Japan and the United States, whose experimentation will eventually influence what many men will wear.

Clothes that look as if they were bought a size too large, a trend shared with many designers of women's clothes, was only one of the recurring themes of the show. Also to be noted:

* Black as a favorite color along with Japanese designs and those influenced by the Japanese look.

* Intentionally wrinkled fabrics, especially linen, and sometimes unevenly dyed to heighten the texture of the fabric.

* Open necklines and shirts worn over pants, exaggerating the easy-cut fit.

* Suspenders, or braces, revived as a way to hold up baggy pants.

* Boxer shorts, briefer than usual, which are replacing stretch briefs on European beaches.

* Hardly a jean to be seen.

"Expensive clothing has been so serious, it is necessary for everything to loosen up," said Pinky Wolman, the designer for Pinky & Dianne. Her clothes are squarer and boxier than last year, with shirttails preferably worn over the trousers, and shirts, even tuxedo shirts, worn open at the neckline. "It's kind of an 'I-don't-care look,' " explained the designer. Even the shorts she likes for next spring are wide and baggy. "Men's legs aren't really sexy, but somehow wide shorts are kind of sexy."

"Clothes that are oversized have a look that is old and comfortable and expensive," said Gene Pressman, one of the designer/owners of the company called Basco. Pressman's partner, Lance Karesh, has always liked to wear his father's old clothes, which have inspired the collection. "The low-slung fit, wider lapels and pants full in the thigh come from these old clothes, but look very modern to me again," said Karesh.

If baggy clothes are an old American look, they are also an integral part of the look from such newly influential Japanese designers as Rei Kawakubo of Commes des Garc,ons, whose business worldwide has doubled in the last year. Her men's clothes are far more conservative than her women's designs, but still the men's jackets are square-cut with no back vent and the pants are pleated with a fairly wide leg.

More startling are the fabrics. Everything, even the wool, is wrinkled from having been prewashed. "It makes them look rough and natural," explained Marion Greenberg, Commes des Garc,ons' American representative. The rumpled, textured effect is heightened because the fabrics have been dunked in a blue Yuzen dye and put in the sun to dry. "It looks like they forgot to get out all the bluing in the wash," whispered one buyer checking out the line for the first time.

But if the tint is blue, the dominant palette at Commes des Garc,ons and other Japanese designers is black. "It simply sells the best," said Tony Perse, owner of the trendy Los Angeles boutique that changed its name from Maxfield Blue to just Maxfield because it sells so much black clothing. "Black looks great on everyone. It is simple, graphic and goes with everything," added Perse, whose calling card is black and whose store catalogue is called "Black Mail." The Christmas item he expects to be snapped up by his regular customers, who include Rod Stewart, Jack Nicholson and Barbra Streisand, is a handmade bicycle, all in black, of course, that will retail for $2,000.

For thank-you notes, Maxfield has stationery that's black, too.