SAN FRANCISCO >> Microsoft is trying to skewer Google as a lousy holiday shopping guide in its latest attempt to divert more traffic to its Bing search engine.

The attack starts Wednesday with a marketing campaign focused on a recent change in how Google runs the part of its search engine devoted to shopping results. The revisions require merchants to pay Google to have their products listed in the shopping section.

In its new ads, Microsoft Corp. contends the new approach betrays Google Inc.’s longstanding commitment to provide the most trustworthy results on the Web, even if it means foregoing revenue. To punctuate its point, Microsoft is warning consumers that they risk getting “scroogled” if they rely on Google’s shopping search service.

The message will be highlighted in TV commercials scheduled to run on NBC and CNN and newspaper ads in The New York Times, The Wall Street Journal and The Washington Post. The blitz also will appear on billboards and online, anchored by a new website, Scroogled.com.

The barbs are likely to inject more antagonism into an already bitter rivalry between two of the world’s best-known and most powerful technology companies.

Google’s search engine is dominant on the Internet, with Bing running a distant second. Microsoft’s Office and Windows software remains an integral part of personal computers, but Google has been reducing the importance of those programs and PCs with the success of Web-based services and its Android operating system for smartphones and tablet computers.

Google still doesn’t require websites to pay to be listed in in its main database. That’s the index providing the results for requests entered into Google’s all-purpose search box. A query made there for a particular product, such as computers, will still include results from merchants who haven’t paid for the privilege of being included.

But anyone who clicks on a tab at the top for shopping-specific results will see only listings for paying merchants. That means results from sites, including Web retailing giant Amazon.com Inc., aren’t displayed unless they pay. Amazon so far has only occasionally paid to have some of its wares listed in Google’s shopping section. Zappos, a site owned by Amazon, has been more willing to pay the price to be listed in Google’s shopping results.

Google defends the fee-based approach as a way to encourage merchants to provide more comprehensive and accurate information about what they’re selling.

“I think you just get a well-organized set of product information, ways to buy it, and really have a great experience there,” CEO Larry Page said during a conference call with analysts last month.

In a statement late Tuesday, Google said it’s pleased with the response to the new shopping system, which offers listings from some 100,000 sellers.

Google, like Microsoft, also accepts payments for ads that are triggered by specific search terms and appear to the right or on top of regular search results. Those are labeled in gray letters as ads.

Since its inception in 1998, Google has tried to cast itself as a force for good while depicting Microsoft as a ruthless empire.

But Google has become less cuddly as it has established itself as the Internet’s main gateway — and through that, as a well-oiled moneymaking machine. The Mountain View, Calif., company’s search engine is so influential that government regulators in the U.S. and Europe have been investigating whether Google has been stifling competition by giving special preference to its own services in search results.

Microsoft, which faced its own antitrust inquiries more than a decade ago, is among the companies that had prodded the investigation of Google. This time, it’s pouncing on Google for straying for from its own principles.

Since mid-October, Google’s shopping section has included only listings from merchants who paid to be included in the results. In some cases, the order of the shopping results has been dictated by how much money Google received for the listing. The change coincides with what is expected to be the most lucrative holiday shopping season on the Web yet.

Google discloses that it receives payments in small print at the bottom of the shopping results page. The notice is also visible if a user clicks on a link at the top of the shopping results page, under the heading: “Why these products?”

What’s left unsaid is the omission of sites such as Amazon, which often offers some of the best deals on the Web.

The financially driven system for determining the results in a major part of Google’s search engine breaks new ground for a company whose idealistic founders, Page and Sergey Brin, once railed against the perils of allowing money to influence which Web links to show.

Brin and Page preached about the issue in academic papers that they wrote about search while conceiving Google as Stanford University graduate students. They also delved into the topic when discussing Google’s “don’t be evil” creed in a letter written when the company went public in 2004.

“Our search results are the best we know how to produce,” Brin and Page wrote in the letter. “They are unbiased and objective, and we do not accept payment for them.”

Microsoft contends that Google is doing a disservice to its users with the new approach, as many users may not even realize that the results in shopping search are being swayed by money.

“We want consumers to know in contrast to route that Google has pursued, we are staying true to the DNA of what a good search engine is really about,” said Mike Nichols, Bing’s chief marketing officer. “We will rank results on what’s relevant to you and not based on how much someone might pay us.”

Microsoft once accepted payments that can affect the order of results. But the Redmond, Wash., company said it hasn’t accepted payments since it re-branded its search engine as Bing in 2009.

Bing’s shopping section includes merchant listings for Shopping.com, a service that gets referral fees. Microsoft said the payments don’t influence how Bing ranks its shopping results.

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Online:

Microsoft’s attack site: http://scroogled.com

Google shopping site: http://www.google.com/shopping