A running rivalry between Internet giants Facebook and Google has ramped up a notch – and in an unusual manner, as a secretive attempt to plant bad publicity became public knowledge.

Facebook acknowledged that it hired a prominent public-relations firm to promote a negative story line about Google. It was supposed to be kept quiet that Facebook was the client behind the PR pitch.

The bid backfired when, rather than running with the story from PR firm Burson-Marsteller, journalists dug into the promotion and discovered that Facebook was the real promoter. The result: egg on the face, or worse, for a social-networking company that has already had its share of negative publicity. The incident also tarnishes Burson-Marsteller.

But beyond the immediate ruckus, the fouled-up media campaign points to a serious battle between fast-growing Facebook and Google over who will be the Web's preeminent domain.

Let's just say that Facebook hasn't pushed its "like" button for Google. And when Google recently launched its competing "+1" button, it wasn't with the idea of helping its users friend Facebook.

On the surface, the rivalry may seem needless. Facebook runs a social network. Google helps people search for online information. Each can be profitable in separate spheres, so can't they get along?

It's a little like the old "Oklahoma!" song that says the farmer and the cowman should be friends. Both companies do different things, but like farmers and ranchers, they also compete for resources. In this case, it's not land or water, but audience: the time people spend online and the advertising revenue that can go with that.

On top of that, these two companies are so big that they almost can't help bumping into each other. They compete for the title biggest or most-trafficked website.

Google is a big provider of social services including e-mail, as well as a go-to source for content like news. Similarly, Facebook has become a major platform for people to share news and information and has launched partnerships designed to carve into Google's dominance in online searches.

Fairly or unfairly, Google enjoys the better reputation – although both have been criticized for eroding user privacy with little notice.

Facebook has fought back over the past year with policies to give users more influence over how much of their personal information becomes public.

The latest incident is a PR setback – even though, ironically, Facebook's goal was to draw attention to Google policies that it viewed as improper. Employees of Burson-Marsteller promoted the idea that a Google service called Social Search is mining people's personal information and sharing it without their knowledge or consent. (Google and some third-party analysts say the service doesn't tread on privacy.)

“No ‘smear’ campaign was authorized or intended," Facebook said in a statement given Thursday to the technology website Search Engine Land. "Instead, we wanted third parties to verify that people did not approve of the collection and use of information from their accounts on Facebook and other services for inclusion in Google Social Circles" – a feature of the Social Search tool.

For its part, Burson-Marsteller issued a statement of regret Thursday. "The client requested that its name be withheld on the grounds that it was merely asking to bring publicly available information to light and such information could then be independently and easily replicated by any media," the firm said. "Whatever the rationale, this was not at all standard operating procedure and ... should have been declined."

A recent Harris Interactive poll found that Google had the best reputation of 60 large companies. In the annual survey of US adults, Google moved from third place to first, while Facebook was ranked No. 31.

Then again, Facebook's effort at planting negative stories about its rival may not be rare in the fast-moving and high-stakes world of technology. It's not unusual, say high-tech insiders, for firms to seek to influence the news media to cast competitors in an unfavorable light.

"[W]hat stands out about this case is that Facebook went after Google in such an underhanded way over such a weak claim, and that it failed in its efforts so publicly," writes Eric Eldon for the news website Inside Facebook.