The case is the first smartphone dispute to be heard by the agency since Google Inc. (GOOG) said Aug. 15 it would buy Motorola Mobility for $12.5 billion to obtain patents that could be used as a bulwark against a surge of lawsuits targeting handsets and tablet computers that use Google’s Android operating system.

“We have a responsibility to our employees, customers, partners and shareholders to safeguard our intellectual property,” David Howard, Microsoft’s corporate vice president and deputy general counsel for litigation, said in an e-mail. “Motorola is infringing our patents and we are confident that the ITC will rule in our favor.”