SAN FRANCISCO — Joining the herd of websites jostling to cash in on the holiday shopping season, online search engine leader Google Inc. is adding a tool designed to make it easier for consumers to map out their local trips to the mall.

The feature, to be unveiled Tuesday at Google's Froogle shopping site, will pinpoint the merchants selling a specific item within a designated ZIP code. Besides displaying a map showing all the local stores carrying the merchandise, Froogle also will list price differences.

The Mountain View, Calif.-based company developed the free tool to help consumers avoid the frustration of traveling to a store that no longer has an item on their shopping lists, said Marissa Mayer, Google's director of consumer products.

Froogle, a comparison shopping site that Google launched three years ago, will continue to give visitors the option to buy the merchandise online. Google receives a commission for the online referrals.

Initially, Google is depending on a contractor to pull the inventory information from several hundred major merchants.

The search engine hopes to make the service even comprehensive by encouraging stores to submit their own customized merchandises list to the newly created "Google Base" — an information clearinghouse for everything from family recipes to scientific formulas.

Froogle will pull the product inventory lists from Google Base and include them in its index, Mayer said.

With the busiest shopping season just days away, other major shopping comparison sites also have been upgrading in a bid to lure more traffic. Yahoo Inc., perhaps Google's biggest rival, recently expanded its shopping site so it spans 90 million products, up from 60 million a year ago.

Froogle hasn't been nearly as successful as Google's main search engine, which has reigned as the Internet's most popular for several years. In the comparison shopping niche, Froogle ranked as the fifth largest site with 6.36 million unique U.S. visitors during September, according to Nielsen/NetRatings Inc.

The top two comparison sites — E.W. Scripps Co.'s Shopzilla and eBay Inc.'s Shopping.com — each attracted about 15 million unique visitors. They both advertise heavily on Google and Yahoo to lure much of their traffic.