The Senate next month will consider a resolution that would impose economic sanctions on South Africa unless “significant progress” in eliminating apartheid is made by March, Sen. Richard G. Lugar (R-Ind.), chairman of the Foreign Relations Committee, announced. The resolution, introduced by Sen. Charles McC. Mathias Jr. (R-Md.), was approved by the panel last spring. If it became law, it could ban U.S. investment in South Africa, the importation of Krugerrand gold coins and the export of U.S. computers to South Africa.