(Updates with loan detail)
By Alexandra Alper and Roberto Aguilar
MEXICO CITY, Sept 3 (Reuters) - Mexico's government on Wednesday unveiled the winning design for a new, futuristic, spider-shaped airport for the capital that will ease delays and boost capacity at a cost of 120 billion pesos ($9.17 billion) in public and private funding.
British architect Norman Foster and Fernando Romero, a son-in-law of Mexican tycoon Carlos Slim, showcased their winning, airy design in the form of an X with arching spans at the presidential palace.
The new six-runway project will be built next to the Benito Juarez International Airport on the eastern flank of Mexico City, where the government already owns land.
"This airport is the first of its kind in the world," Foster said. "It doesn't have a conventional roof. It doesn't have vertical walls. It doesn't have columns in the normal sense."
He cited challenges that include frequent earthquakes and the fact that the capital lies on a lake bed.
Telecoms and Transport Minister Gerardo Ruiz Esparza said he expected construction to start in mid-2015.
The government is in negotiations with U.S. engineering firm Parsons to take on the role of construction manager, he said.
Mexico's government will finance the first stage of the new airport and aims to issue up to 30-year bonds to finance later stages, a senior project official said.
Federico Patino, financial director of the project, said it would be financed through 2016 using money from the government's budget and two loans totaling up to $3 billion, and backed by earnings from the current airport.
The first loan is $1 billion from banks BBVA, HSBC , Grupo Financiero Inbursa and Citigroup and is set to close next month, Patino said.
After 2016, Mexico would seek to complement budget funds for the project with the issue of dollar-denominated 30-year bonds to the tune of $6 billion, he added.
Factoring in projects including construction management and water-related issues on the site will raise the overall cost of the airport to 169 billion pesos ($12.9 billion).
Ultimately the government hopes to boost capacity to 120 million passengers a year within 50 years.
Ruiz Esparza said that the current airport would close, with the land being used for university buildings and cargo.
The project follows an abortive bid to build a new airport near the chosen site under former President Vicente Fox. That effort met with violent protests in which demonstrators armed with machetes and Molotov cocktails took 19 officials hostage after the government initially offered locals around 70 cents per square meter for land. It was canceled in 2002.
Foster is one of the world's most famous architects, and his practice, Foster + Partners, has designed dozens of high-profile projects around the world, including Beijing Airport and London's Wembley Stadium.
His firm also designed a London office building later nicknamed "the Gherkin" for its rounded shape, which has become one of the city's leading landmarks.
Romero is married to Soumaya Slim, a daughter of one of the world's richest men, and is the head of FR-EE Fernando Romero Enterprise.
The firm designed Mexico City's distinctive Museo Soumaya, which houses much of Slim's personal art collection behind its sloping, silvery walls.
Slim, who controls Mexican telecoms giant America Movil , is behind a diversified empire that spans mining, banking and retail. Analysts say Slim's Grupo Carso and builder ICA are likely to bid for construction contracts. (1 US dollar = 13.0997 Mexican peso) (Additional reporting by Dave Graham and Christine Murray; Editing by Simon Gardner, Cynthia Osterman, Dan Grebler, Lisa Shumaker and Gopakumar Warrier)