Yahoo said yesterday that it would start charging companies that want to ensure that their Web sites are included in its Web index from which research results are selected.
The practice, called ''paid inclusion,'' has long been a part of many search engines including Microsoft's MSN search function and Ask Jeeves. But Google, which last year surged ahead of Yahoo to become the No.1 site for searching on the Internet, disdains the practice as misleading.
Last month, Yahoo replaced Google, which had operated Yahoo's search engine, with its own technology to index billions of Web pages. Yahoo says it hopes to include every site on the Internet it can find in that index at no charge. But sites that pay for Yahoo's new program can guarantee that they are included in the index.
Yahoo will update its index of paying clients every two days, while it may update its listing of other sites once a month. And Yahoo will give paying clients detailed reports on when its users click on their sites and will help those sites improve their listings.
The paying sites will be intermingled with others in Yahoo's main search results listings, which are separate from the advertising called ''sponsor results'' on top of and to the side of Yahoo's search results.
Yahoo said that although sites would be able to pay to be in the index, its computer system would still pick the most relevant site for each search, without regard to payment status.
''What our users care about is the relevancy of results, not whether the source paid to participate,'' said Tim Cadogan, a vice president in Yahoo's search unit. He pointed out that many companies hire firms that specialize in tweaking Web pages so that they rise in search rankings.
Yet executives at several of those firms say that paying to be included in search indexes often does help paying sites jump ahead of nonpaying sites: paying sites are allowed to submit additional information, in a so-called data feed, which helps the search engine associate their pages with a given topic.
''Almost without fail, any time we submit a feed, stuff that was nowhere to be found on a search engine pops up to the top,'' said Gord Hotchkiss, president of Enquiro, a search consulting firm.
Sites will pay from $10 to $49 for each Web page indexed and from 15 cents to $1 each time a Yahoo user clicks on a link to their sites.
Safa Rashtchy, an analyst with Piper Jaffray, estimates that this paid-inclusion program will produce $100 million a year in revenue for Yahoo.
Mr. Cadogan said that the purpose of the program was simply to offer Yahoo users more relevant information. He added that Yahoo would give some nonprofit organizations like the Library of Congress the ability to add pages to its index without paying. (While Yahoo's paid inclusion program is available to any business that can enter a credit card number on its Web site, the nonprofit version will be open only to a select group of organizations.)
Yahoo says its program is in compliance with Federal Trade Commission guidelines on paid inclusion programs because the payments are disclosed to any user who clicks on the ''what's this'' link that appears on each search.
Larry Page, a co-founder of Google, argued that such disclosures were not enough. He compared search results with the news articles in newspapers or magazines, which are independent of advertising.
