U.S. Secretary of State Warren Christopher has called them "weapons of mass destruction in slow motion"--the 110 million land mines buried in 68 countries stretching from Cambodia to Costa Rica. The United Nations has estimated that they kill or maim roughly 20,000 people each year. Most of the casualties are innocent civilians, many of them children, because practically all of the mines in place today have no self-destruction or neutralization features. They remain deadly hazards long after a conflict has ended or the lines of confrontation have moved. With some 23 million land mines buried in its sands, Egypt has more unexploded mines than any other country. Many of these date from World War II, and the others are from the 1948, 1956, 1967, and 1973 Arab-Israeli wars. The most densely mined country is Bosnia and Herzegovina, where there are an average of 152 mines per square mile. As international publicity and abhorrence to these indiscriminate killers have grown, so have the public and private efforts to remove the mines already planted and to ban or at least severely restrict their use in the future.