Google's business model reflects that twofold desire. In many ways, the search engine has come to resemble a free-circulation newspaper that makes its profit by selling ads. In Google's case, the company gives away the search engine for free to Internet users seeking information on the Internet, and then, like the newspaper, makes its money on clearly marked ads.

One difference is that in a free-circulation newspaper, top dollar can buy prime positioning for ads. But on Google, just being the highest bidder doesn't guarantee that an ad will appear in the top-tier position.

The ranking of ads on Google is the product of two factors: the price a company is willing to bid on keywords and the frequency with which consumers click on the ad. Even if a company bids higher on certain words than any other firm bids, if consumers are not clicking, that ad will move down to a less prominent spot.

Google said it takes this approach so that computer users see the most relevant ads first. Industry experts say the practice also makes good business sense since Google gets paid only when consumers click on an ad.

"They don't want dead ads at the top of their Web site," said Scott T. Newman, president of US Markerboard, who spends a few hours each day tweaking his ads and bids and said he has built a profitable, growing business entirely through search. "They give you a little bit of a break if you get a good click-through rate."

In contrast, Yahoo guarantees that the highest bidders for words will show up at the top of the list of sponsored ads. Industry specialists said this is one of a number of differences in style between the competitors.

Yahoo "is strictly capitalistic. Pay more and you are number one," SiteLab's Todd said. "Google has more socialist tendencies. They like to give their users a vote."

The science of consumer behavior on the Internet is still young, but some early evidence shows differences between how men and women use search engines. A recent survey by iProspect.com Inc., a leading search engine marketer, found that 15.2 percent more women than men said they abandoned search results and looked elsewhere if they did not find what they were looking for on the first page.

"Someone targeting homemakers must be found on the first page," said Fredrick Marckini, founder and chief executive of iProspect, whose clients range from Citibank to the New England Journal of Medicine. "Most importantly, all research confirms that if you are not found on the first three pages of the search results, the top 30 matches, you have built a billboard in the woods. No one will find it."

Google remains the undisputed market leader in search, Marckini said. According to a recent analysis by StatMarket, Google has a 41 percent market share in the United States and a growing edge over second-place Yahoo, which has 27.4 percent, and Microsoft Corp.'s MSN, with 19.6 percent.

Google's free or "natural" search results are not influenced by payments, a practice it described as "evil" in its recent IPO filing. That was a shot at Yahoo, which does accept fees from companies to ensure that they are included in its searches. Some in the industry say that as a public company or when its growth slows, Google is likely to be tested on this and other practices on which it has staked out purist positions.

Yesterday, Andy Beal, vice president of WebSourced Inc., said search industry insiders were surprised by Google's launch of a new product that includes banner ads that advertisers could choose to place on Web sites of some of Google's smaller partners. To Beal, it sounded as though Google might be bending its lofty principles in a grab for more ad revenue. "Is Google starting to bow to pressure?" he asked.

But Tim Armstrong, Google's vice president of advertising, defended the company's new ad product, saying it is grounded in the same fundamental approach the company has adhered to in the past: making cost-effective, contextually relevant ads available to computer users on thousands of Web sites that are part of its distribution network. In this case, Armstrong said, the new product, dubbed "image ads," will give advertisers the opportunity to distribute ads with graphics and photos, enhancing their quality. For example, he said a car ad might be more effective if it included a photo of the vehicle.

He also said computer users would have the opportunity to give Google feedback on the ads during the beta test. The ads will appear in one of four configurations, one of which is the traditional banner ad. "This is a natural link from what we are doing now," Armstrong said. "We have the same core principles. We are sensitive to the fact that we want image ads to be useful."

At the same time, Google's filing for an IPO -- in which the company plans to auction shares to investors of all sizes in a manner influenced by the way it auctions keywords -- has sparked a new kind of chatter among the specialists who spend their days bidding on words.

"Everyone is trying to figure out if they are going to bid and how much they are going to bid," iProspect's Marckini said.