LAS VEGAS (Reuters) - The first shops could throw open their doors in the redeveloped World Trade Center by March 2015, Australian mall operator Westfield said on Monday, 13-and-a-half years after the New York landmark was destroyed in the September 11 attacks.

The redevelopment of the World Trade Center is years behind schedule and billions of dollars over budget.

After years of negotiation, Westfield last week signed a deal with the Port Authority of New York and New Jersey for a $1.25 billion joint venture to lease the retail space at the World Trade Center.

Westfield, one of the world's biggest mall owners, said the first retailers for the redeveloped site could be announced by the first half of 2013, with an opening date set for March 2015.

Potential tenants of the rebuilt World Trade Center got a peak at what the new shopping area may look like during a trade conference in Las Vegas on Monday.

Westfield Co-Chief Executive Peter Lowy said 352,000 sq feet of shopping would be spread over three above-ground levels and two below ground.

Westfield is also entitled to operate another 90,000 sq feet of retail space among the 8.8 million sq feet of office space under construction.

Lowy said Westfield planned to be selective about possible tenants.

"We're going to do something that no one can imagine," Lowy told Reuters during the International Council of Shopping Centers annual convention, or RECon.

He declined to give further details.

The stores will cater not only to the people who will live and work at the World Trade Center, but also to the masses of tourists who visit the National September 11 Memorial Park and Museum, as well as the proposed performing arts center.

"We have to design the retail to suit the customer," Lowy said.

He said he expects tenants to be a mix of upscale food shops, a "very good" supermarket and other U.S. and international retailers.

The above-ground retail will be housed in 4 World Trade Center, which is under construction, and inside 3 World Trade Center, which is still in the planning stage. Most of the retail will be inside the Transportation Hub, a central stop for 13 train lines.

Westfield operated the hugely successful underground mall at the World Trade Center before selling its interest to the Port Authority after the September 11, 2001, attacks.

In February, an independent audit ordered by the governors of New York and New Jersey, who share control of the authority, found that the cost of the World Trade Center redevelopment had soared by $3.8 billion to $14.8 billion.