* SK Eyes LightSquared wireless venture backed by Harbinger
* Investment would mark U.S. re-entry after Helio withdrawal (Adds backgroud)
SEOUL, Sept 20 (Reuters) - South Korea's top mobile carrier SK Telecom Co Ltd said on Monday that it was in talks to invest in U.S. upstart wireless operator LightSquared, a venture backed by hedge fund Harbinger Capital Partners.
"We are in talks with Harbinger to decide investment terms," an SK Telecom spokeswoman said.
The possible investment would mark the operator's reentry into the U.S. market in two years.
SK Telecom exited the U.S. market in 2008, selling its struggling mobile unit Helio to Virgin Mobile USA as part of a divestment of foreign assets. SK Telecom sold back its stake in China Unicom for $1.3 billion in 2009.
LightSquared plans to build an open wireless broadband network using Long Term Evolution (LTE) technology, a fourth-generation protocol that established operators Verizon Wireless, AT&T Inc and MetroPCS Communications Inc also plan to support.
The venture said in July that it planned to kick off network construction with $1.75 billion of financing from financial investors, and expected to raise a second round of financing in the next two years.
Nokia Siemens Networks (NSN) will deliver equipment to LightSquared this year so it can test network services in Baltimore, Phoenix, Las Vegas and Denver in the first half of 2011. (Reporting by Hyunjoo Jin; Editing by Chris Lewis)