The National Coalition for the Homeless charged that the Administration is illegally withholding $15 million in housing funds for the homeless. The coalition and operators of shelters for the homeless in Columbus, Ohio, and New York said they had filed suit in Washington to free the money appropriated by Congress this year as part of the $1-billion Stewart B. McKinney Homeless Assistance Act. Under the law, the $15 million in emergency aid to the homeless was to be released by Aug. 21 so the money would be available by this winter. "The White House fought this legislation and lost the battle in Congress," said Maria Foscarinis, the coalition's Washington lawyer. "Now the President is defying Congress. We will not permit it."