By Catherine Hornby

ROME (Reuters) - Salvage crews will employ huge cranes and air tanks to refloat the half-submerged Costa Concordia cruise liner in the largest ever operation of its kind, according to a plan unveiled on Friday.

Estimated to cost at least $300 million, the work is expected to begin within a few days and last about a year, said the ship's operator Costa Cruises, owned by Carnival Corp & Plc.

The 290-metre-long (11,417 feet) cruise liner capsized off the Tuscan island of Giglio after hitting rocks on January 13. At least 30 people died and two are still unaccounted for.

Its captain Francesco Schettino has been accused of wrecking the ship after he brought it too close to shore and faces charges of multiple manslaughter and abandoning ship before all 4,200 passengers and crew were rescued.

Representatives of Titan Salvage of the United States and Italian firm Micoperi, who have been chosen to handle the removal, told a news conference they were confident the plans would succeed even though they have never been tested on a ship this size.

"This will be the largest refloat in history but we think it's entirely possible," said Richard Habib, president of Titan Salvage, owned by U.S. group Crowley Maritime Corp.

The head of Italy's Civil Protection Agency, Franco Gabrielli, said the ship would be stabilized by the end of August to prevent it from shifting down a rocky ledge and plunging into the deep waters of the surrounding marine reserve.

Two cranes attached to a underwater platform beside the 114,5000 metric ton vessel will pull it upright, along with big water-filled tanks that will be fitted on the part above water.

Once upright, tanks will be fitted to the other side of the hull and then all the tanks will be emptied and filled with air to refloat the huge liner.

Micoperi manager Silvio Bartolotti said the ship would be refloated by February 2013.

It will then be towed to an Italian port and broken up. The port of Livorno may be chosen in order to compensate the Tuscany region by creating jobs, regional president Enrico Rossi said.

Some 2,300 metric ton of fuel were removed in March, averting an environmental disaster.

Costa Cruises president Gianni Onorato said protection of the environment during the salvage operation and guarantees for the local tourist industry would be key priorities.

Once the ship is towed away, the seabed will be cleaned of debris and work will be undertaken to restore marine flora.

(Reporting By Catherine Hornby; Editing by Sophie Hares)