Every three months, Google (GOOG) reports the state of its $1 billion investment in AOL (TWX) in its quarterly report to the SEC. Over the summer, Google admitted the investment "may be" impaired. Now it says it "is" impaired. But at the end of September, the company didn't believe the impairment was "other-than-temporary."

That could change this quarter, Barclays analyst Doug Anmuth predicts in a note this morning. Specifically, Anmuth thinks Google will write down approximately $500 million of its $1 billion investment, resulting in a charge of about $1.17 in GAAP earnings per share. Even that would value the investment at $10 billion, which, Anmuth notes, is higher than the $6 billion valuation he estimates.

Anmuth: "We are not surprised that Google would write down its investment in AOL given AOL’s recent results of declining advertising revenues and our projection of continued declines for the remainder of 2008 and throughout 2009. Interestingly, while we project negative growth at AOL’s display and Third Party Network over this period, we project AOL’s search business, powered by Google, to grow."

Anmuth's commentary was part of a report in which he slashed his Q4 Google revenue estimate to flat quarter-over-quarter growth, based on a slowing ad market. Anmuth expects Google to post $4.05 billion in Q4 sales, below the Street's $4.31 billion consensus.

See Also:

Analyst: Google Won't Escape The Economy

Google's Era Of YouTube-Like Experiments Is Over

Google Subletting Office Space At NYC Googleplex