How do you find a bride these days?

One of the nation’s leading online tracking companies knows.

Monitoring consumers at roughly 3,000 Web sites, Revenue Science identified brides by picking out bridal behavior it had seen: anyone who’d gone online to read about weddings in the news, entered “bridesmaid dresses” into a search engine or surfed fashion pages for wedding styles.

The company found 40,000 such people, whom it knows by random number, not name, and sent them a tailored online ad.

“A successful campaign,” according to company president Jeff Hirsch.

The growing practice of “behavioral targeting,” or sending ads to online users based on their Internet habits, is now under scrutiny by the Federal Trade Commission, whose review could shape not only Web advertising rules but the character of the Web itself.

For while public interest groups argue that compiling profiles of largely unsuspecting Internet users ought to be illegal, online advertisers and publishers respond that their ad targeting tactics protect privacy and may be essential to support the free content on the Web.

Behavioral targeting allows many Web sites to raise ad prices, because advertisers will pay more when they can isolate a particular audience.

Limiting behavioral targeting could “jeopardize the consumer’s ability to get free content on the Internet,” a spokesman of the Newspaper Association of America, a trade group that represents the business interests of most U.S. dailies, including The Washington Post, Paul Boyle, said.

The FTC is considering guidelines, for now voluntary, that would make it harder to target behavior. The principles were issued in December after town hall meetings, and the public comment period ended last month.

As the commission’s deliberations begin, some federal and state lawmakers are weighing measures that would be mandatory. New York lawmakers, for example, are considering a law similar to the FTC guidelines.

Now that many Americans spend as much time interacting with the Web as they do watching TV, there is a wealth of information available for targeters: what articles a person reads in online newspapers, what queries he or she types into search engines and what items the person shops for.

Revenue Science and its peers say that because the user profiles they keep are organized by randomly assigned numbers, no personally identifying information is ever stored.