Hundreds of anti-nuclear demonstrators gathered at a handful of nuclear weapons manufacturing plants and testing sites to commemorate the 25th anniversary of the Cuban missile crisis. In Colorado, Rep. Patricia Schroeder addressed about 600 anti-nuclear protesters outside the Rocky Flats nuclear weapons plant, where radioactive contamination has been found in the soil at the southeast corner of the plant. Fearing seepage into underground water, Rockwell International Corp., which operates the plant, will spend $17 million to clean up the site. Smaller demonstrations were held in Cape Canaveral, Fla., Quonset Point, R.I., Valley Forge, Pa., and Mountain View, Calif. There were 28 arrests. Several hundred people attended the rally in Mountain View, which is near a Lockheed missile facility in Sunnyvale.