Google Inc. is preparing to sell wireless service directly to consumers after striking deals with Sprint Corp. and T-Mobile US Inc., a move likely to prod the wireless industry to cut prices and improve speeds, according to people familiar with the matter.

It isn’t clear how widely the Internet search giant plans to offer wireless service, how much it will cost or when it will go on sale. Google might start small by limiting the new service to certain U.S. cities or to users of its Google Fiber broadband Internet service.

The move is one of the strongest signals yet that Google, based in Mountain View, Calif., is stretching its ambitions far beyond YouTube videos and the Gmail email service. Google executives also want the company to have a major role in how those services are delivered to consumers.

Sprint, of Overland Park, Kan., is the third-largest wireless carrier, while T-Mobile, of Bellevue, Wash., ranks fourth. Under separate agreements with each carrier, Google will resell service on the Sprint and T-Mobile networks, according to people familiar with the plans. Such wholesale agreements are common, essentially allowing sellers such as Google to pitch wireless service under their own brand names.

Google’s entry into the mobile-phone business would create a new headache for an industry already struggling with a price war and soaring costs for wireless spectrum. Sprint executives are betting that the boost from an influx of new Google customers outweighs the risk that the Internet search giant will learn too much about the ins and outs of the wireless business.