The innovative art group Art Attack assaulted the northeast corner of 12th and U streets NW yesterday, planting its latest political statement upon a vacant lot's fertile ground. "Used War Lot" is an installation "in the context of a used-car lot" said Art Attack's director Lynn McCary, associate director of programs at the Washington Project for the Arts (though the installation is not supported by the WPA). It opened yesterday to coincide with both the anniversary of the Battle of Antietam and the International Day of World Peace, marked on the third Tuesday of every September.

Performance artist Jared Hendrickson opened the installation with a piece that mimicked the behavior of a used-car salesman. One of the sculptures in the installation resembles the Vietnam Veterans Memorial. But, it is covered with pages of the D.C. telephone directory.

"We try to do our work in unexpected places. We're not really doing this for the gallery world."

Washingtonians were entertained by one of Art Attack's last projects -- whimsical, multicolored, life-size silhouettes "falling" down the side of the Lansburgh Building, 420 Seventh St. NW. The project's ghost still haunts the building, though the exhibit closed a while ago.

"We couldn't reach one of the figures," said McCary of the lone figure that still occupies the side of the building.

"Used War Lot" is up until Oct. 19. Open Studio Tour

During National Arts Week next week, the National Endowment for the Arts will celebrate its 20th anniversary. The Washington Project for the Arts will join the celebration with its Seventh Annual Open Studio. Every year 300 artists open their studio doors to the curious public. On two successive weekends beginning Saturday, studio hounds can drop by the WPA at 400 Seventh St. NW or Herb's Restaurant, 2121 P St. NW, to pick up free maps giving studio locations throughout the metropolitan area. Studios are open from 11 a.m. to 6 p.m. on Saturday in Virginia, on Sunday in Maryland, on Sept. 28 in downtown Washington (Georgetown, Dupont Circle, Seventh Street, etc.) and on Sept. 29 in the remainder of the District. Call 347-8304 for more information. Free Fall Film Series

The Hirshhorn Museum's free fall film series, beginning tomorrow, has something for everyone: from "The Impersonation: Apropos Disappearance of Reginald Pepper," about an artist who may never have existed (Independent Film Series, tomorrow and Friday), to video profiles of artists Jennifer Bartlett, Jonathan Borofsky and Robert Longo (Artist Documentary Series, Oct. 24 and 26) to "Back to School: Rock Enrolled," a program of Rocky and Bullwinkle cartoons (Films for Young People, Oct. 5.). The films are shown in the Hirshhorn's auditorium, Independence Avenue at Eighth Street SW. Call 357-2700 for additional program information. Arts, Etc.

On Oct. 5 the Baltimore Museum of Art will, for the first time in its history, open a gallery for the permanent rotating display of textiles from its collection . . . The Third European Film Festival at the American Film Institute continues through Sept. 30, with guest appearances at some screenings by foreign film directors. Call 785-4601 to confirm dates of appearances and for a program schedule . . . The Kennedy Center Education Program is sponsoring a fall workshop series for educators and the public called "Focus on the Arts." The program features performances, discussions, lectures, tours and teaching workshops. Call 254-7190 to request a brochure . . . The National Endowment for the Humanities has awarded the Folger Shakespeare Library $84,188 for an exhibit and conference to commemorate the 100th anniversary of poet Emily Dickinson's death next spring.