The submission in response to the city's "request for proposal" was handed in this week, the companies said in a joint statement. Earthlink and Google last year told the city separately that they were interested in building the project.
The city wants to build a municipal network in order to give poorer residents an affordable option for getting online. Mayor Gavin Newsom launched the wireless broadband initiative last summer, hoping to provide free Internet access to city businesses and residents.
"This proposal presents a unique opportunity for both companies," Donald Berryman, president of Earthlink's municipal networks unit, said in a statement. "By coming together to leverage the strengths of both companies, we will be able to offer services to different customers on the network that fit with their own individual needs and wants."
Under the joint proposal, Google would provide the free Wi-Fi service citywide, and Atlanta-based Earthlink would be the Internet service provider, the Mountain View, Calif., search engine said.
"We have submitted this proposal because at Google we're focused on creating new technologies that make it easier for people to quickly access the world's information," Google said Wednesday in a statement. "It is also a way for Google to support the local community."
Google has said it does not intend to build other wireless broadband networks.
San Francisco is among several cities looking to build municipal networks. Telecom and cable providers, however, are lobbying Congress to prevent cities from building public networks that would cut into their businesses. Those companies include BellSouth, Comcast, Cox, Qwest, SBC, now called AT&T; and Verizon.
Pennsylvania and Virginia have passed laws restricting the use of municipal networks. California, however, has no such restrictions.