Fortuitous coincidence brings the sculptural works of Michael Todd and John Sanders to the same downtown building for solo exhibitions this month. Both artists work in the venerable modernist tradition of abstract welded steel, and both have a sensuous touch. But the expressive results, if not at opposite ends of the pole, are heading that way fast. This makes for a sharp contrast at 406 7th St. NW, where Todd is showing on the ground floor at Barbara Kornblatt's gallery and Sanders up one flight at Ramon Osuna's.

Todd's pieces, most of them based upon circles and arcs, are extremely assured, refined, light, airy--amazing things, really, considering they are made of steel rods, tubes, cubes, plates, wires and hardened puddles of molten metal, all of which Todd bends, folds, rumples, twists and turns as if he were a master calligrapher scribbling in the air for the fun of it. It is, in fact, Todd's justifiable conceit to name this the "Enso" series, using a Japanese word, popular with calligraphers, meaning "endless circle."

The largest of the works, "Ako's Enso," is a tour de force standing maybe 10 feet high; the other works measure perhaps three feet in diameter. Each involves the spatial tension of the not-quite-closed circle, and the release of sharp, witty punctuation marks in the form of asymmetrically placed pieces of lacquered steel.

Todd, who now works in New York City, taught during the mid-1960s at Bennington College, then the stronghold of the Anthony Caro esthetic of crisply thought-out welded steel sculpture. This once-dominant esthetic produced work never less than pretty and often more, but led to quantities of not quite first-rate art, and often worse. Todd's recent works represent this sculptural approach at a point of extraordinary refinement--a point fortunately balanced by strength.

Sanders begins with big, solid cylinders or slabs of steel, cuts them this way and that, and welds them together to form weighty ensembles, most of which seem impassable, almost monolithic. In keeping with this theme of contradiction (making monoliths from many pieces) he also cuts into these solid chunks with an oxygen-acetylene torch, producing gashes and irregularly serrated edges that seem wildly at variance with the hardness of the material.

These edges and gashes have an almost liquid feel about them, a quality intensified in the pieces on view at the Osuna Gallery, which are not the original steel sculptures but bronze casts made from them.

The contrasts between rich, brown patinas and muscular abstract forms, surface and mass, sensuousness and strength provide more of the ironic surprises at the heart of this work. Sanders has established a lot of possibilities in these works, including the temptation of over-ripeness. It will be interesting to see where he moves from here.

Todd's works will remain on view at the Kornblatt Gallery through Feb. 23. The Sanders show continues at the Osuna Gallery through Feb. 4. Both places are open from 11 a.m. to 6 p.m. Tuesday through Saturday. Mexican Yarn Paintings

Folk art is an endangered species. Threats include commercialization, overexposure and the daily incursions of modern life which eat away at the collective perceptions that make it possible. So it is always a great pleasure, if increasingly a surprise, to come upon a folk expression of full, rampant vitality, as in the current exhibition at Gallery K of yarn paintings by Jose Benitez Sanchez.

Sanchez, a Huichol Indian, was born in Mexico. The Huichol are a marginal group that retreated into the mountains even before Corte's arrived. In the centuries since the conquest the group has managed to maintain its distance, its hard way of life and its spiritual values. Sanchez's paintings, made with strands of yarn (in all the brilliance of their synthetic dyes) pressed into beeswax, depict with indelible vitality the rich mythological cosmos of the Huichol.

This is a significant achievement, the result of tremendous concentration. Sanchez's paintings, although basically symmetrical, teem with spirit-life. The technique suits the vision: The linear patterning of the strands of yarn, in this artist's hands, takes on an intense liveliness in perfect sync with the myths and tales being pictured. To call Sanchez a first-rate folk artist is in no way demeaning, but in fact he may be something else, a hybrid sort of artist existing between two worlds. Sanchez speaks Spanish and is acculturated to the contemporary world, a position of great stress and also of great promise.

The exhibition continues through Jan. 29 at Gallery K, 2032 P St. NW, open from 11 a.m. to 6 p.m. Tuesday through Saturday. Steve Estrada's First Solo

Steve Estrada's paintings, on view in his first solo exhibition at the Olshonsky Gallery, come in two types: a "Galileo" series, which concerns measurement and magic and consists of canvases of different sizes and shapes stacked in front of one another; and a catchall sort of series, which concerns the artist's memories, his nightmares, his studio and his muddled thoughts about recent art history, among other things.

About the latter it is hard to say whether Estrada is doing too much or too little. The combination of figuration, symbolic image and dream image doesn't quite come off, nor does the bevy of techniques and materials (thin washes, big impastos, traditional drawing, hard edges, collage elements) quite meld, nor do the sources (Rauschenberg, Dine, abstract expressionism, neo-expressionism) make much sense. Nonetheless, the paintings have a reckless sort of energy and are very interesting to look at. The Galileo paintings, ingeniously structured (especially "Galileo III"), are more delicately handled, sort of Joseph Cornells writ large, but too large.

The show continues through Feb 5 at the Olshonsky, 443 7th St. NW (second floor), open from noon to 6 p.m. Tuesday through Saturday.