(Adds comment from future transportation minister, slump in regional airport stocks)
MEXICO CITY, Oct 11 (Reuters) - Mexico's incoming government will hold a four-day public consultation to decide the fate of the capital's part-built new airport and will upgrade facilities at the existing airport to ease congestion, a member of the next Cabinet said on Thursday.
Incoming transport minister Javier Jimenez Espriu said the public would be polled from Oct. 25 to Oct. 28 on whether the government should finish the ambitious new Mexico City airport or scrap it and upgrade a military air base to complement the existing hub.
"This is going to be taken seriously. Even if there are three votes, we will take it seriously," Jimenez said at a news conference, adding that results would be released the following week.
Mexican President-elect Andres Manuel Lopez Obrador, who takes office on Dec. 1, has said the new airport has been tainted by corruption and will be more costly than projected.
Mexican regional airport stocks GAP, OMA and ASUR fell by between 3 percent and 5 percent.
The cancellation of the project would hit regional airports since 70 percent of domestic flights originate from the capital, said Alejandra Marcos at brokerage Intercam.
If the project is scrapped, it would spook investors and could hit the Mexican peso and government bonds, she said.
Jimenez said the airport, which has been under construction on the drained bed of Lake Texcoco on the eastern flank of Mexico City since 2015 and is around 20 to 30 percent complete, was over budget and behind schedule.
He said the Texcoco airport was now projected to cost 285 billion pesos ($15 billion) compared with an original estimate of 195 billion pesos. The airport had been due to be completed during 2022, but Jimenez said it would likely take until 2024.
The consultation will be held in over 500 municipalities covering about 80 percent of Mexico's population, Jimenez said.
Irrespective of the results of the survey, Jimenez said the delay in construction meant "major surgery" was required at the current airport in order to ease stretched capacity limits.
The new government would invest up to 5 billion pesos to upgrade the current Mexico City airport and expand an international airport in the city of Toluca in the State of Mexico, about 34 miles (55 km) from the capital, he added.
The aim is to lift capacity at the Mexico City airport from around 40 million passengers per year to 50 million and increase Toluca annual traffic from less than 4 million to 10 million. ($1 = 18.9680 Mexican pesos) (Reporting by Daina Beth Solomon; editing by Jonathan Oatis and Rosalba O'Brien)