They work in city streets and they ambush the observer. They're guerrillas and they're artists and they're already here.

Thirteen of their cadre -- from Baltimore, New York, Cuba and Los Angeles -- have infiltrated Washington. Already they have hit the sidewalks of downtown, the ruins of Northeast, 14th Street and Georgetown. Avoiding white-walled galleries, they prefer to launch their art attacks on cemeteries, vacant lots, and the nicely tended lawns just outside the White House. Their tactics are subversive or, at least, mischievous. They rely upon surprise.

If you see a pedestrian begin to dance the fox trot in front of the House of Wig on 13th Street near H Street, you may blame a guerrilla.Ruth Turner stole the footprints and the arrows she has painted there from the how-to-do-it diagrams in a book by Fred Astaire.

You may have seen the rays of light that Merle Tempkin sent shooting from a chain-link baseball backstop in West Potomac Park. She hung countless painted mirrors on its metal fencing. Guerrillas do not always win. cHer "Mirror Piece for Phyllis" is no longer there. The authorities moved quickly and made her take it down.

Some guerrillas strap white crosses to their backs and walk the streets of Washington disguised (if that's the word) as religious kooks. The voices that surround them come from hidden tape recorders. "Don't wear slacks," the voices said. "Don't divorce. Don't be a loudmouth. Don't commit adultery. Oh, no, don't." Steve Seemayer, their leader, has done this sort of thing before in Southern California.

Even weirder are the plans drawn by Lou Forgione on a triangle of lawn between the Corcoran and the White House. Forgione, who paints grass with the powdered lime used by groundskeepers for goal lines, says he's come to town to reveal a "top secret." The subject of his piece is a "hypersonic wind tunnel" discovered, so he says, in 1952. It makes energy, he says.

What is going on here is a show called "Streetworks" organized by Al Nodal, director of the Washington Project for the Arts. The artists he has chosen are extending a tradition forged by street performers, dadaists and the people who did happenings. "I brought them here," Nodal says, "because guerrilla art is happening all over the country. Young artists in increasing numbers are rejecting the art system and going to the streets. The issues they're concerned with are social and political, rather than esthetic. Guerrilla art is growing. In the next few years, I promise you, you'll see more of it around."

Unlike so-called earth artists, guerrillas tend to leave the still-unspoiled countryside to the birds and bugs. Though some of them, the wackiest, do add to art pollution, at least they work in cities. They do not place huge works of art on deserts or on seashores as the late Robert Smithson did and as Christo does.

Some guerrillas, it is true, are not wholly reputable. Frederick Braitwaite and Lee Quinones -- both were members once of the Fab Five graffiti group -- got their start in art spraying New York's subway cars. In Washington they've sprayed their names, and falling bombs and phrases, on a wall on Ninth Street across from the entrance of the National Museum of American Art. Their piece quotes Andy Warhol: "Art is anything you can get away with." They call their work, with reason, "premeditated visual crime." While here they both were houseguests of curator Nodal, and they sprayed his hallway good and proper before they left town.

Some guerrilla art has strong social content. Jon Peterson, for instance, has made shelters for Washington's street bums. John Fekner, who has opened an "information store" at 1225 G St. NW, is against pollution. "Big Sale!" scream his day-glo store-front ads, "Toxic Waste! PCB! DDT! BVO!"

Candace Hill-Montgomery has installed her piece on a grassy plot between the Rayburn Building and the U.S. Department of Health and Human Services. Once she put a picket fence around a building's wreck in Harlem. Her new work, "Fuel for Thought," includes nice linoleum walkways and three painted kitchen cabinets full of ethnic food.

Anna Mendieta ponders death. The figure she has slipped just beneath the grass of a cemetery hill beside Wisconsin Avenue -- it is positioned there face down, as if its arms and toes are reaching out toward the center of the earth -- will sink away eventually. It is made of earth covered with fresh sod. Lannelle Newell, a Washington guerrilla, prefers to work with tires.She stacks them into walls and towers, and then paints them with bright colors. Her "Big Tire Story" may be seen amid the rubble of a vacant lot between Third and Fourth streets on K Street NW.

Not all guerrilla art is preachy, loud or ugly. The most beautiful and modest pieces in the "Streetworks" exhibition are those made by Judith Simonian and Maura Sheehan.

Simonian's wall painting at 14th and Chapin Streets NW is a thoughtful piece of urban archeaology. Her site is the ruin of a market that was torched during the riots of 1968. With white spray and with black paint she has made what one might call the ghost of a step pyramid out of those blank walls.

Maura Sheehan has transformed a shattered, useless structure into something dazzling. It stands on Rhode Island Avenue at 18th Street NE. sBefore the kids began to toss rocks through its glass walls, it was a working greenhouse. Now it's literally green. Sheehan has painted its broken panes with a color she calls "extract of emerald." That former eyesore now suggests shining lizards lounging in the capitol of Oz. If you drive out to see it, keep your eyes peeled to the right. For Sheehan has brought color to the eight coal silos at Rhode Island Avenue and 8th Street NE.As a kind of visual appetizer, she has painted all the coal chutes of those tall, imposing concrete cylinders that same lizard green.

The bum shelters of Peterson are already missing: Bag ladies put them in their bags; bums took them away. Maura Sheehan's greenhouse will continue to disintegrate, and Forgione's lime lines will soon soak into the earth.But the ideologies that motivate these artists -- a desire to be rid of the galleries' sterilities, the money game, and art that's for the few, that has no social content -- will not soon fade away.