Business Notes SOFTWARE

Get ready for a rumble in software. Lotus and Microsoft, the top independent U.S. producers of personal-computer programs, each announced plans to invade the other's turf. The battleground: the $400 million market for spreadsheets, or electronic business ledgers. Microsoft, which sells Excel software for Apple Computer's Macintosh models, plans to adapt its program for IBM- compatible computers. Lotus, which designed the best-selling 1-2-3 program for IBM machines, promises to bring out a version of that software for the Mac. Microsoft -- led by Bill Gates, its boyish-looking billionaire chairman -- may have an edge. The IBM version of Excel has fancier features than 1-2-3 and arrives in stores by the end of October. The new 1-2-3 will not be out until 1988.