The U.S. Small Business Administration is considering a new loan-guarantee program for revolving lines of credit, secured mainly by receivables and inventory. If adopted, the program would be funded with existing SBA loan money. That's a big "if," however. The SBA had bad experiences with short-term loans in the 1970s, and officials don't want to repeat past mistakes. Then, too, they may be concerned about possible White House opposition to a new federal guarantee program.