UPDATE 1-EMC seeks U.S. approval on Data Domain purchase

* EMC refiles request for U.S. approval to buy Data Domain

* Move restarts 15-day clock for fast-track approval

BOSTON, June 17 (Reuters) - EMC Corp (EMC.N) has refiled its request for U.S. government antitrust clearance to buy specialty storage company Data Domain Inc (DDUP.O) as its first request expired on Wednesday.

The U.S. Federal Trade Commission only began investigating the bid from EMC, as well as one from rival NetApp Inc (NTAP.O) on Monday in a rare corporate bidding war.

EMC, the world's biggest maker of corporate data storage equipment, filed its original request for government clearance to proceed with its $1.8 billion offer for the company two weeks ago.

U.S. regulations require that the government either approve the acquisition within 15 days or launch a more intensive investigation into the matter. Such reviews can drag on for months, depending on the complexity of the deal.

By refiling its application EMC gave the FTC another 15 days to give the proposed acquisition fast-track approval.

"We believe we will receive regulatory approval in a timely manner," EMC General Counsel Paul Dacier said in a statement.

(Reporting by Jim Finkle; Editing by Richard Chang)