By Chris Aspin

MEXICO CITY, Feb 21 (Reuters) - Mexican airport operator Asur will fight to take part in the bidding process for a planned airport in the Riviera Maya region which will drain passenger traffic away from its key runways at the resort of Cancun.

Chief Financial Officer Adolfo Castro said on Thursday Asur (ASURB.MX: Quote, Profile, Research)(ASR.N: Quote, Profile, Research) will take the case to court if government authorities do not allow the company to bid for the rights to build and run the airport in Quintana Roo state.

The government has not yet decided if Asur can participate in the bidding process. The sticking point is competition because Asur already operates nine airports in Mexico's southeast, including Cancun.

"If they do not allow us to participate we will use all the legal tools that we have in hand in order to protect our rights and in order to be part of the bidding process," Castro told a conference call with analysts.

The government wants Riviera Maya airport because the region, just south of Cancun, is a booming tourist area especially around Playa del Carmen, which is popular with U.S. and European visitors.

Castro said the airport, which could cost between $120 million and $200 million depending on its size and facilities, would take time to construct because it is in an area with no infrastructure.

"As I understand this is going to be located in the middle of the jungle. Provisional works will have to be performed to construct this airport. I believe that can take between three to four years at least," Castro said.

But once built, it will hit Cancun airport, which currently accounts for 70 percent of Asur's passenger numbers.

"Cancun airport passenger traffic will suffer because I'm sure that some of the traffic that is going today south of Playa del Carmen will go to this airport. I don't have a real estimate but if you want to put a real number there it could be 20 percent (of Cancun traffic)," he said.

On Wednesday, Asur posted a fourth-quarter net loss of 191 million pesos after a huge tax charge of 489 million pesos in the period. Asur reported a net profit of 136 million pesos in the fourth quarter of 2006.

The government of President Felipe Calderon introduced a new flat rate business tax at the start of this year and Asur opted to set up new deferred assets and liabilities provisions ahead of the changes.

Asur's local shares were down 0.23 percent on Thursday to 60 pesos. (Editing by Tim Dobbyn)