HuffingtonPost co-founder and business head Ken Lerer is stepping down from his current responsibilities, paidContent.org has learned, and a new CEO announcement should be coming as soon as tomorrow. Lerer, a former EVP at AOL (NYSE: TWX) Time Warner, never really had a formal title at the start-up but was the business head and effective CEO. He’s probably not leaving as he is an investor in the company, and was also involved with HuffPo’s recently closed second $5 million round of funding, which we wrote about first here.

We’re still working to confirm the identity of Lerer’s successor, but expect it to be someone with mainstream media and online news experience — especially as HufPo’s big moment with the presidential campaign and elections is now and next year. More as we know it.

Update 1: The FT is reporting that Betsy Morgan, SVP and GM of CBSNews.com since July 2005, will be announced as CEO. That fits with what we heard earlier. Morgan also has worked in media investment banking.

—Lerer told the FT HuffPo is “now breaking even some months.”

Update 2: I spoke briefly to Larry Kramer, our board member and former head of CBS (NYSE: CBS) Digital (he recruited Morgan over from CBS News), who outlined the challenge Morgan has: “Her challenge will be to help build the site and business into something larger than Ariana herself…to give it its own value and personality.”

Meanwhile, the announcement is out with some more details. Morgan will oversee all operations and strategy for the site. Lerer will be chairman of the board, a new post. Arianna remains Editor-in-Chief. Morgan told the NYT she sees her new role as a business position, not a journalism one.

Disclaimers: Greycroft also invested in our company, and we have a small headline syndication deal with HuffPo on its media page