UPDATE 1-XM, Sirius extend merger deadline by 2 months

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NEW YORK, Feb 29 (Reuters) - XM Satellite Radio Holdings Inc XMSR.O and Sirius Satellite Radio Inc (SIRI.O: Quote, Profile, Research, Stock Buzz) have extended by two months a deadline to potentially terminate without penalty Sirius's year-old proposed acquisition of its bigger rival.

Under the original terms of their deal, first announced in February 2007, the companies could have walked away after March 1 if they did not receive regulatory approval.

U.S. regulators, including the Federal Communications Commission and Department of Justice, have yet to decide whether to approve the merger. Both companies said this week that they are optimistic both agencies will approve the deal.

The deal's strongest critics, including the traditional radio industry, charge that combining the two U.S. satellite radio companies would be anti-competitive.

XM and Sirius have said that with the bulk of new satellite radio subscription coming along with the purchase of cars, the relatively small satellite radio industry would merely be one entertainment option for consumers already using high-definition radios, iPods, and backseat televisions.

The friendly deal, valued at about $4.6 billion when it was announced, called for XM shareholders to receive 4.6 Sirius shares for each XM share held. It would bring under one roof programming by Howard Stern, Oprah Winfrey, Bob Dylan, Major League Baseball and the National Football league.

Shares of both money-losing companies have slumped since one year ago, with Sirius shares off about 20 percent and XM shares down about 16 percent. (Reporting by Franklin Paul, editing by Phil Berlowitz)