With the revisions, Yahoo believes its search engine will provide more useful information than Google's and be simpler to use. The rebuilt version will combine Google's index with Yahoo's customized services spanning sports, driving directions and weather reports.
"We think this is going to change the game a bit," said Jeff Weiner, Yahoo's senior vice president of search and marketplace. "This is the first of many steps toward reinforcing our leadership in the marketplace."
Google declined to comment on Yahoo's new search engine.
Battle lines clearly are being drawn between the companies, said Danny Sullivan, editor of the industry newsletter Search Engine Watch.
"They are going to be duking it out," Sullivan predicted. "Clearly, Yahoo would like to keep more people from going over to Google to search and maybe even bring back some of the people that have previously left."
Toppling Google won't be easy. In just five years, Google has become synonymous with online searching.
Yahoo played a vital role in Google's rise. After encouraging Google to create its search engine, Yahoo raised the startup's profile nearly three years ago by licensing Google's software to run the searches on its popular online portal.
According to the industry newsletter, Google handles an average of 112 million searches a day and Yahoo handles about 42 million. Most of Yahoo's results are generated by Google's software.
With its success, Google has introduced other services, such as news and shopping pages, that traverse Yahoo's turf.
To lessen its dependence on Google, Yahoo last month bought search engine specialist Inktomi for $279.5 million. Yahoo plans to incorporate Inktomi's tools in to its search engine by year's end.
Success also has thrust privately-held Google into the crosshairs of Microsoft Corp., which last week said it would improve its online search prowess.
By Michael Liedtke