SAN JOSE, Calif. – Google on Tuesday switched on a new program that will dramatically improve the accuracy of its speech recognition service, which allows people to use verbal commands to search the Internet, send an e-mail or post a Facebook update.

That’s of growing importance to the Mountain View, Calif., search giant, which sees Internet searches on smart phones as a significant part of its business. While the company doesn’t disclose specific numbers, one in four searches on Android devices are now done by voice, and the search volume on Android phones climbed by 50 percent in the first six months of 2010.

“A lot of the world’s information is spoken, and if Google’s mission is to organize the world’s information, it needs to include the world’s spoken information,” said Mike Cohen, who heads the company’s speech efforts.

Users of the latest Android-powered smart phones can now allow Google to recognize the unique pattern of their speech by downloading a new app from the Android Market. The service gradually learns the patterns of a person’s speech and eventually will more accurately understand their voice commands.

Google’s ambitions don’t stop at improving voice recognition. Its recent purchase of Phonetic Arts, a British company that specializes in speech output, highlights Google’s plans to allow your computer or smart phone to speak back to you.

Google earns the vast majority of its revenue through search advertising, and expects a majority of its Internet business to flow through smart phones and other wireless devices in the future, so high-quality voice services are of critical importance.

The linguistic models that Cohen’s team has helped develop over six years at Google, based on more than 230 billion searches typed into and speech inflections recorded from millions of people who used voice search, are now so vast and complex that it would literally take several centuries for a single PC to create Google’s digital model of spoken English.

For Google, said Al Hilwa, an analyst with the research firm IDC, “voice is a critical strategic competence.”

Google’s Dec. 3 announcement of the Phonetic Arts acquisition — terms were not disclosed — is “complementary to what Google is doing in social networking, video and mobile where it should be possible for people on the go to talk to their mobile devices, search engines or social networks as an alternative mechanism of interaction,” Hilwa said.

Speech also is another key area where Google competes with Microsoft.