By Philip Pullella

VATICAN CITY (Reuters) - Pope Francis will decide for himself if he chews coca leaves in order to ward off altitude sickness when he lands next week at La Paz, Bolivia, the highest international airport in the world, the Vatican said on Tuesday.

A Bolivian minister said on Sunday that Francis had told government officials that he would like to chew coca leaves - the major ingredient of cocaine - when he visits..

But spokesman Father Federico Lombardi, responding at a briefing on the trip where several questions revolved around the Argentine pope and the Andean coca leaf, said he did not know if any such request had been made.

"I am not aware of that," he said. "The pope will do what he thinks is most opportune."

At just over 4,000 meters (13,000 feet) above sea level, La Paz airport, appropriately called "El Alto". The city is below the airport, at about 3,650 meters (11,975 feet).

Local people for centuries have chewed coca leaves to ward off the effects of altitude.

"There are popular customs that people use. Some drink coca tea and others chew coca leaves. Let's see what he decides to do. You can do it too (chew coca leaves), if you want to," Lombardi told reporters.

The coca leaf debate prompted one Hispanic reporter to interject out loud: "Hey, it is not a hallucinogen."

The unprocessed leaf is legal to use and still widely chewed in Bolivia and other Andean countries. Many indigenous people, including Bolivian President Evo Morales, defend its use and consider it a sacred plant.

For health reasons, the 78-year-old Francis, who lost part of one lung to disease when he was a young man, will be in La Paz for only about four hours before moving on to Santa Cruz.

(Editing by Louise Ireland)