Everyone knows about the P Street Strip, headquarters for the city's commercial gallery scene. But it's time for a name change. Welcome the P Street Loop!

Gallery fans are getting some new blocks for Christmas -- city blocks, that is -- reaching north from P Street, up 21st Street, and past the Phillips Collection, Barbara Fiedler Gallery, Fonda del Sol and Wade Gallery to Connecticut Avenue and south again to Dupont Circle.

In addition to the 13 galleries on the old P Street Strip between 20th and 22nd Streets NW, there are now 13 additional stops on the new loop, including a new dealer in antiquities called Trocadero. It adds a rare and welcome dimension to Washington's primarily 20th-century market.

There are also enough eateries, crafts galleries and boutiques to keep a day's outing interesting, all within yards of the Dupont Circle subway stop.

A tour of the loop can begin (or end) at any point along the way, but we began at the Haslem Gallery, 2121 P St., where John Winslow, one of the best of the proliferating realists in town, just opened a rare downtown show.

Now 40, Winslow was born here, trained at Princeton and Yale, and now teaches at Catholic University. This show, his best to date, includes a prodigious number of landscapes and studio interiors, all painted within the past two years.

The landscapes focus casually but intimately on the Potomac and surrounding cliffs and woods, all filled with enthusiastic and admirable painting. They share not only the look but the feel of a solitary walk in the woods. In one chilly scene, the leaves seem to crunch underfoot. The watercolor landscapes are, oddly, stiffer than the oils. It is usually the other way around.

But it is Winslow's paintings of his studio interior that command the most attention. Sticking close to home, Winslow uses himself, his family and friends as elements in classic, solidly constructed still lifes, redolent of the artist's world.

Throughout, Winslow combines traditional pictorial conventions with elements of recent art, notably in his color. In the best and newest painting called "In the Studio, March 1978," he implies movement with the formal device of the blur, currently used by photographers. His work has nothing to do with photography, nor with photo-realism, but here he raises the issue, adding a provocative contradiction.

But it is the internal complexity of these paintings that keeps the viewer's eye and mind busy and happy. There is always something more to look at beyond the studio itselt -- a view out the window, into a mirror, or at a painting hanging on the wall or perched on an easel. There are paintings-within-paintings throughout Winslow's work, sometimes his own and sometimes reproductions of old masters. All reinforce the sense of continuity with art that has gone before. Through December.

Heading north on 21st Street past the Phillips Collection, a Yuri Schwebler sculpture comes into view in front of the Barbara Fiedler Gallery, 1621 21st Street. Now showing inside are the woodcuts of a Japanese-born artist now living in Canada, Naoko Matsubara. Sometimes lyrical, sometimes strong, Matasubara is often murky when she strays from specific natural forms. Several large and striking clay "Vessels" by Frank Ozereko, professor of art at Auburn University in Alabama, have the look of ancient ritual bronzes, and will have particular appeal for ceramic enthusiasts. Through December.

At the Wade Gallery, 1726 21st St., Susan Weil is showing works made of paper, her sole medium for the past 20 years, long before the current paper craze.

Often working in series, Weil tears, crumbles and folds paper, sometimes using subtly colored ink washes, all for the purpose of making three-dimensional poetic gestures which often allude to time and movement.

"Dusk to Dawn," for example, in a wholly abstract way evokes a sense of changing light and the passage of time. In 'Straight as Round," seven pieces of painted paper hung on a curve, hint at the curvature of the horizon.Through December.

Around the corner, the Local 1734 Art Collective, at 1734 Connecticut Ave., a tiny silkscreen establishment incorporating the former P Street Paperworks, is showing 12 silkscreens by its artists, all assembled for a worthy calendar now on sale for $20. Individual prints are available at $5

Other budget-priced works include a fabric piece by Laura Seldman, using a color photo-transfer process that suggests interesting possibilities for commissioned works. Moon Works, a Chincoteague crafts shop, is also showing jewelry, pottery and blown glass through Dec. 10.

Local 1734 is seeking public support to keep its gallery going. As one of the few spots in town where new artists can submit work for jurying and subsequent showing, it deserves support. It has kept itself afloat by printing T-shirts for any occasion, which it still does. Photographs go on view Dec. 14.

Venable Neslage Gallery at 1742 Connecticut Ave. has a mixed bag of prints, some paintings by Albanianborn Zois A. Shuttie are worth a look by those who like old-world traditional scenes. Now living in the United States, Shuttie recently showed at the Atlantic Gallery in Georgetown. We missed it.

The big find of the week, and the real reason for walking all around the block, is Trocadero, a museumlike shop at 1608 20th St. that handles Oriental and European bronzes and porcelain, wood sculpture from New Guinea and Africa, rugs and textiles from Asia and the Middle East, and even has a case of pre-Columbian textiles and artifacts. Everything has been well-researched and prices seem extremely reasonable.

"We sell exports, not imports," says David Kenny, a former chemist turned art agent, who has traveled widely and insists that more good pieces of the sort he sells are going out of the country than are coming in at the moment.

Most of the objects at Trocadero "have some age," as they say, like a fine New Guinea piece from the Sepik River. Others have a great deal of age, such as a 5th-century ceramic horse from China and a pale, beautiful Shinto priest's robe from 1820. An old bit of jade and a pair of French mother of pearl opera glasses lurk irresistibly in a locked case. Two tiny early American editions, at a dollar apiece, proved too irresistible, and left with me.

The last time a gallery showing old art and artifacts appeared on P Street a few years back, it lasted only months. With luck, Trocadero will find a more appreciative audience.

Just a few doors away, at 1606 20th St., is the A.D. Smull Gallery, now moved in from Kensington to join the P Street Loop crowd, and featuring fiber art, wearable art and ceramics. Upstairs, it has been joined by a new Art Deco shop.

One block closer to Dupont Circle, Photo-Graphics, a new photography gallery at 1522 Connecticut Ave. serving corporate and private clients, is catching on fast, and Eirinn & Co. had just opened at 1524 Connecticut Ave. In the same block is venerable old Veerhoff Galleries at 1512 Connecticut Ave., which had a drawer full of minor Piranesi prints when last visited. Washington Womens' Arts Center is just around the corner at 1821 Q St.

Gallery 10 at 1519 Connecticut Ave. ended this Loop Tour with a strong show of sculpture by David Staton, featured in the recent Corcoran Area Show. Anyone who has picked up a piece of wood on a beach, or in a forest, knows the easy virtues of wood that looks like something else.

Staton, however, sees strength and majesty in all wood -- sawed tree-trunks with the bark intact, sliced lumber, stacks of split firewood. He then structures and combines these chunks of tree into sculpture which evokes the majestic landscape from whence it came. "Rockfind" and "Hedgerow" are particularly strong. Through December. CAPTION: Picture 1, "In the Studio," by John Winslow ; Picture 2, Wood carving at Trocadero, by Ellsworth Davis.