Greenbelt, a city that prides itself on its heritage as a New Deal-era social experiment, is finding its commitment to inclusiveness tested as two black candidates contend for seats on its all-white City Council in Tuesday's elections. Until this year, only two blacks had ever run for the council and none had been elected, even though blacks account for nearly half the 21,000 residents of the 6-square-mile city just outside the Capital Beltway, according to the most recent census estimates. Asians and Hispanics make up 20 percent. The disparity has caught the attention of the American Civil Liberties Union and...