Rouble weakness weighs on Comstar Q3 profit

* Earnings fell 26 percent in dollars to $26.9 million

* Affected by foreign exchange effects, interest costs

* Revenue declined in dollars, rose in roubles

* OIBDA decreased to $152 million from $195 million

MOSCOW, Nov 17 - Russian fixed-line telecoms operator Comstar <CMSTq.L> said third-quarter net profit fell 26 percent to $26.9 million mainly due to foreign exchange effects as the rouble weakened and to higher interest expenses.

Sales declined 11 percent in dollar terms to $375.1 million, Comstar, part of services conglomerate Sistema <SSAq.L>, said on Tuesday, while rising 15 percent in roubles.

"The significant weakening of the Russian rouble against the U.S. dollar since September 2008 adversely impacted the group's U.S. dollar reported results," Comstar said in a statement.

Comstar recorded $4.3 million in foreign exchange losses against a $4.5 million forex gain in the third quarter of 2008, when its net profit amounted to $36.4 million.

Interest expenses doubled to $29 million in the third quarter from a year earlier.

Operating income before depreciation and amortisation fell to $152 million from $195 million a year ago, and the OIBDA margin slid to 40.6 percent from 46.2 percent.

In rouble terms, OIBDA edged up 1 percent but net profit slipped 3 percent, also reflecting a 27 percent increase in operating expenses in roubles.

MTS <MBT.N>, Russia's top mobile operator, bought a 51 percent stake in Comstar from Sistema last month and will include its results in its consolidated financial statements from the fourth quarter of 2009. (Reporting by Maria Kiselyova; Editing by Dmitry Sergeyev/Will Waterman)