Yahoo Inc., which removed adult products and banner ads from its U.S. Web portal in 2001 after protests by conservative groups, is back in the pornography business.

With the acquisition of Overture Services last month, Yahoo is now selling ads to a range of hard-core Web sites. Those ads appear on two search engines Yahoo acquired as part of the Overture deal — AltaVista and AlltheWeb .com.

Yahoo’s latest embrace of the adult industry has attracted little attention until now. The Sunnyvale company has kept the adult ads off its popular U.S. portal, which has a mainstream image.

Instead, the ads appear only on what are relatively small Web sites that few Internet users identify with Yahoo. The ads are also exported to Web sites outside the Yahoo family such as InfoSpace, which owns its own branded search engine, plus Dogpile and Metacrawler.

A Yahoo spokeswoman declined to address questions about Yahoo’s adult business directly. Nor would she say whether its expansion in that area represents a change in company policy.

In a statement, she said: “Our intention is to ensure that consumer interests are best served and that consumers, advertisers and partners benefit from the highest quality online experience. We evaluate the external environment of our various businesses, as well as our practices, on an ongoing basis.”

That Overture sells adult ads isn’t new. Nor is the fact that those ads appear on AltaVista and AlltheWeb.com.

All of those Web sites did business with the adult industry long before Yahoo took charge of them in October with its $1.8 billion acquisition of Overture.

The adult ads appear as links on AltaVista and AlltheWeb after users enter search queries such as “porn” and “XXX.”

Yahoo banned most adult-related business on its U.S. portal in 2001 after protests by such conservative groups as the American Family Association. The issue came to a head after Yahoo created a special adult shopping category on its Web site.

Yahoo’s response was to remove adult products from its shopping, auctions and classifieds sections. Executives also banned new contracts for adult banner ads.

Around the same time, Yahoo took modest steps against pornography posted by users on its Yahoo Groups message boards.

The company made it more difficult to find adult-oriented groups, by deleting them from the Groups directory. However, it didn’t eliminate the groups themselves or crack down on what was posted in them.

Yahoo has been more liberal overseas. Ads for adult Web sites continue to run on some of Yahoo’s international portals, such as the one for Germany.

Yahoo isn’t the only Internet company doing business with the adult industry. For example, Google features adult ads for certain searches while EBay has created an adult products category, accessible only after users enter their credit card information.

Charlene Li, an Internet industry analyst for Forrester Research, a market research firm, said that other media firms also have shifting standards.

She said Disney, for example, is known for children’s films, but some of its subsidiaries have released R-rated movies. “I think it is quite consistent with what media companies do across the world,” Li said.

Cable companies, for example, offer pay-per-view X-rated films in some hotels.

Li said Yahoo might drop the adult ads if enough users complained.

“Even if the money is significant in the U.S. and most people object, I think Yahoo would decide that they are better off losing one audience and keeping the other,” Li said. “There’s a trade-off calculation.”