CHICAGO — Moody's Investors Services said today that it has lowered its rating on Walgreen Co.'s senior unsecured debt from A1 to A2.

The Deerfield, Ill., drugstore chain's recently aborted unsolicited buyout bid for rival Longs Drug Stores "reflects a clearly more aggressive financial policy," the rating concern said, and indicates that "the likelihood of Walgreen's making debt financed acquisitions has increased.

"Moody's also noted that there is "greater uncertainty surrounding the company's future strategic direction and financial policies, given the sudden retirement of its chairman and chief executive officer on October 10."

Walgreen CEO Jeffrey Rein unexpectedly stepped down from the top job Friday, two days after Walgreen threw in the towel on its unsuccessful $2.8 billion effort to acquire Longs. Walgreen's now conducting a search for his successor.

In his 28 months as CEO, Rein implemented a number of strategic moves designed to help the historically conservative company adapt to changes in the industry.

Moody's, which had placed Walgreen debt under review in mid-September, affirmed its Prime-1 rating on Walgreen commercial paper. And it said the new, lower A2 rating (which is still solidly investment-grade) is based on Walgreen's "very stable operating performance and its strong market position in the retail pharmacy industry."