SAN FRANCISCO, Aug. 15 — Even as it rolls out a local wireless Internet service in the city where it is based, Google says it has no plans to position itself as a national provider of such services.

The free service in Mountain View, the company’s base in the heart of Silicon Valley, will become generally available on Wednesday after nine months of testing. Google has been selected by the city of San Francisco to install and operate a similar service there in partnership with Earthlink; the two companies are negotiating with the city over the terms.

There has been widespread speculation that Google might compete nationally as a wireless Internet provider, but an executive said Tuesday in a phone interview that Google had embarked on the Mountain View and San Francisco efforts with other objectives: to demonstrate the value of competition in providing Internet access, and to build systems that would allow the company to experiment with new business ideas.

Competitive Internet access has been a crucial issue for Google’s executives, who have jousted publicly with telephone and cable industry companies that have threatened to charge content providers for access to networks. The debate has extended to Washington, where Google and its allies have called for regulators and legislators to ensure what proponents call “Net neutrality.”