AT& T, IBM, Intel, Microsoft . . . Google?

In this respect, the proposed $3.6 billion purchase of DoubleClick is not particularly troubling. The one area of Internet advertising that Google doesn't yet dominate is in the area of those often-annoying display ads, and its purchase of DoubleClick would give Google an instant lead in that fast-growing market. More significantly, it would allow Google to leverage its lead in search advertising by bundling it with DoubleClick's display advertising services, just as Yahoo and Microsoft intend to do with their recent display-advertising purchases.

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There's no reason for the government to block the DoubleClick purchase outright. But as a condition of approval, the Federal Trade Commission should get binding assurances from Google that it won't require advertisers or publishers to buy the bundled product or enter into exclusive contracts with publishers or advertisers to prevent them from using other services as well.

On the other hand, there would be a serious antitrust problem if Google were to strike some sort of deal with Facebook, the social-networking site. In the space of three years, Facebook has attracted 40 million users, proved itself as a powerful advertising medium and attracted the attention of hundreds of companies designing applications to run on its platform.

For many of those users, Facebook is their first point of call on the Internet, or the place they hang out. That success suggests the possibility that it might one day challenge Google's dominance by changing the way people use the Internet and offering advertisers an even better mechanism for targeting their messages. It would be folly for the Federal Trade Commission to allow Google to foreclose that possibility before we see how things develop.

Google executives bristle at the idea that government intervention might be necessary. Their line is that a do-no-evil company such as Google would never, ever put the interests of its shareholders ahead of its users or society in general.

"We really do believe that stuff," said chief executive Eric Schmidt, who claims to have spent too many years at other companies fighting Microsoft's thuggish tactics to now engage in them himself.

I don't doubt the Google Guys' sincerity. But as the histories of Ma Bell and IBM remind, the path to monopoly profits is often paved with good intentions.

Steven Pearlstein will host a Web discussion today at noon athttp://washingtonpost.com. He can be reached atpearlsteins@washpost.com.