There's already no love lost between Facebook and Google in the realm of social networking. And now Facebook has been caught trying to spread some some additional ill will toward its would-be rival.

Public relations giant Burson-Marsteller confirmed to CNET this morning, rather ruefully, that Facebook hired it in what USA Today, which broke the initial story, has called a "whisper campaign" intended to stir up fears of Google violating users' privacy.

Earlier this week, USA Today reported that an as-yet-unnamed company had hired Burson-Marsteller to pitch prominent news outlets on the potential privacy and legal issues surrounding Google's Social Circle feature.

Social Circle allows users to see information that's publicly available for those they're connected with in Google Chat and Contacts. The information includes links to others' Facebook accounts, Twitter feeds, and personal Web sites. Social Circle also allows for access to information of friends of friends, called Secondary Connections.

Just last fall, Google and Facebook engaged in a public and bitter sparring match over how much user data they're willing to share--whether, say, Facebook users could automatically import Gmail contacts, or Google's search engine could index Facebook data.

Burson-Marsteller's recent pitch to at least one blogger included language such as this: "The American people must be made aware of the now immediate intrusions into their deeply personal lives Google is cataloging and broadcasting every minute of every day--without their permission."

Then last night, The Daily Beast's Dan Lyons reported that Facebook was actually behind the campaign, saying a Facebook spokesman had confirmed that the social network enlisted the PR firm's help, ostensibly because of Facebook's concerns over user privacy. The spokesman also pointed to the social network's concern that Google is trying to "use Facebook data" for its own gain, Lyons wrote.

That was enough for the PR agency.

"Now that Facebook has come forward," the Burson-Marsteller spokesman told CNET today, "we can confirm that we undertook an assignment for that client."

According to the spokesman: "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."

And now the PR firm is trying to do some damage control of its own.

"Whatever the rationale, this was not at all standard operating procedure and is against our policies, and the assignment on those terms should have been declined," the Burson spokesman wrote to CNET in an e-mailed statement. "When talking to the media, we need to adhere to strict standards of transparency about clients, and this incident underscores the absolute importance of that principle."

Fighting words from Facebook But Facebook isn't ready to go down without a fight. The social network not only owned up to its actions, it stuck by its claims that Google's Social Circles is a problem.

"You and your readers can look at the feature and decide if they have approved of this collection and use of information by clicking here when their Google account is open," a Facebook spokesperson said in an e-mailed statement to CNET. "Of course, people who do not have Gmail accounts are still included in this collection but they have no way to view or control it."

Facebook stopped short of apologizing for its actions, but it acknowledged that it wished it handled the situation differently.

"No 'smear' campaign was authorized or intended," the spokesperson told CNET. "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--just as Facebook did not approve of use or collection for this purpose.

"We engaged Burson-Marsteller to focus attention on this issue, using publicly available information that could be independently verified by any media organization or analyst," the spokesperson continued. "The issues are serious and we should have presented them in a serious and transparent way."

Google did not immediately respond to request for comment on Facebook's charges.

A continued locking of horns between the two online giants is inevitable. Google operates its own social network through Gmail, called Google Buzz. Though that service likely won't catch up to the mammoth Facebook, it's a competitor nonetheless. And Facebook is becoming a more sizable threat to Google in the online-advertising market. Given Facebook's more than 600 million active users, advertisers are quickly discovering that Facebook's ad opportunity and targeting potential are huge.

Earlier this year, research firm eMarketer reported that Facebook generated $1.86 billion in advertising revenue last year. This year, the research firm expects that number to jump to over $4 billion. In 2012, eMarketer believes Facebook's revenue will grow again to $5.7 billion.

Updated at 9:07 a.m. PT: Added statement from Facebook.