Providence Equity among bidders for Australia's Leighton unit-sources

HONG KONG/MELBOURNE Dec 12 (Reuters) - U.S. buyout firm Providence Equity Partners is among suitors that have advanced to the second round of bidding for Leighton Holdings' Australian fibre-optic network NextGen, sources said, in a deal that analysts estimate could fetch up to A$870 million ($910 million).

Leighton, controlled by Spain's ACS, is selling the inter-city fibre-optic business NextGen and two smaller data businesses Metronode and Infoplex to pay down debt.

Leighton, Australia's largest construction company, has been plagued by losses from the delayed construction of a water desalination plant in the state of Victoria, and a road link to Brisbane airport in Queensland state which opened in July, months behind schedule.

It was not immediately clear who the other short-listed bidders were.

Leighton and Providence declined to comment. The sources declined to be identified as the sale process was confidential.

Leighton could bring in up to A$870 million from the NextGen sale, Citigroup analysts estimate.