UPDATE 2-Harbinger to shed more of Calpine, shares drop

* Harbinger controls 87 million Calpine shares

* Calpine shares drop 4 pct on planned sale (Adds shareholding details from regulatory filings)

SAN FRANCISCO, Sept 22 (Reuters) - Hedge fund Harbinger Capital Partners is offering up to 5 percent of Calpine Corp (CPN.N) for public sale, sending Calpine shares down 4 percent.

Leading shareholder Harbinger is offering 20 million Calpine shares in a secondary offering, or 4.5 percent of the 442.4 million shares outstanding, as well as an option to sell 3 million more, Calpine said on Tuesday.

Harbinger has bet big on Calpine since the power company's emergence from bankruptcy last year, with more than a third of its Master Fund I invested in it even after that fund sold 20.7 million shares in the second quarter, according to filings with U.S. financial regulators.

New York-based Harbinger holds about 87 million Calpine shares in two funds, making it one of the power company's top shareholders after SPO Partners & Co, a Mill Valley, California-based investment firm that held 21 percent at the end of June.

Shares of Calpine, which will not receive any funds from the secondary sale, fell 4 percent after-hours to $11.83, after closing 1.1 percent higher at $12.35. The stock hit a year high of $14.95 in June, recovering from as low as $4.76 in March.

Harbinger's Special Situations Fund has also invested heavily in merchant power company Mirant Corp MIR.N, owning as much as 10 percent of the outstanding shares in November 2008. By the end of June, their Mirant holdings had shrunk to 1.2 percent of outstanding shares, according to SEC filings. (Reporting by Braden Reddall, editing by Leslie Gevirtz)