SAN FRANCISCO — The finance section Google Inc. unveiled yesterday continues a philosophical shift that's turning its once-pure Internet search engine into an all-purpose Web site that seems increasingly interested in getting people to stick around instead of sending them elsewhere.

The evolution has been unfolding during the past four years as Google has introduced free e-mail, news, photo sharing, instant messaging, shopping and mapping services that are staples of one-stop Web sites commonly known as "portals."

The changes have sparked a debate about whether Google is moving wisely to counteract its biggest rivals — longtime Web portals like Yahoo Inc. and Microsoft Corp.'s MSN — or overextending itself in a way that ultimately will diminish the appeal of its Internet-leading search engine.

"There have been concerns that Google is doing just about everything these days but focusing on search," said Danny Sullivan, editor of Search Engine Watch, a closely watched industry newsletter.

Although Google dislikes being described as a portal, Sullivan and industry analysts said its new finance section leaves little doubt where the company is headed.

"They are being fairly careful about it, but they are walking very rapidly toward becoming a portal," said Forrester Research analyst Charlene Li. "They have a lot of other services gunning for them, so they have become most keen about building user loyalty so the users don't have a reason to go someplace else."

By keeping visitors on its site longer, Google gets more chances to serve up the ads that account for virtually all of its profits, although for now, at least, Google doesn't plan to show ads on its finance section.

Finance emerged as one of Yahoo's first specialty sections when the Sunnyvale, Calif.-based company decided to diversify beyond Internet search and began packaging content on its own Web site.

Yahoo's finance section, introduced a decade ago, has turned into one of the company's most powerful traffic magnets. The 31.4 million people who came to Yahoo Finance last month spent an average of 54 minutes per visit on the site, according to comScore Media Metrix.

Google spokeswoman Sonya Boralv said the company remains committed to guiding its visitors to other Web sites with useful information. "Our motivation isn't to provide sticky services," she said.

Unlike Yahoo, Google isn't hiring any writers to produce articles for its finance section, which will provide links to stories by a variety of media. But Google's site will include extensive analytical tools, including interactive charts, that seem likely to keep people on its site for longer periods.

When Google co-founders Larry Page and Sergey Brin founded the company in 1998, they pledged to focus obsessively on Web search and avoid the temptation to diversify into other areas that might distract them.

"Google does not do horoscopes, financial advice or chat," the company once boasted.

The corporate philosophy section of Google's Web site continues to declare: "It's best to do one thing really, really well."

But that same page now includes a footnote to reflect that the company's mindset has changed during the past four years.

"Over time, we've expanded our view of the range of services we can offer ... and products that then seemed unlikely are now key aspects of our portfolio," Google said. "This doesn't mean we've changed our core mission; just that the farther we travel toward achieving it, the more those blurry objects on the horizon come into sharper focus (to be replaced, of course, by more blurry objects)."

Google executives say the company devotes 70 percent of its time on Internet search, 20 percent on peripheral products like the finance section and e-mail and 10 percent on experiments like its recent proposal to build a high-speed Internet service in San Francisco.

Now that Google has launched a finance section, Gartner Inc. analyst Allen Weiner says the company is more likely to add financial planning and personal banking to compete with Microsoft. Google's Boralv said the company expects to add more features to the finance section, but said nothing is immediately planned.

Weiner also says it won't be long before Google offers a specialty section devoted exclusively to sports, just like Yahoo and MSN already do.

Google's expansion already has caused some people to draw cautionary comparisons to AltaVista, a pioneering Web search engine that set out to build a more diversified portal in the 1990s.

The expansion alienated AltaVista's once-loyal users as its search results deteriorated, creating an opportunity for upstarts like Google. AltaVista eventually was sold and its technology is now part of Yahoo's effort to overtake Google in search.

"You would think Google would remember that one of the reasons it exists is because of the dumb things other people once did," Sullivan said.