By Philip Pullella

ABOARD THE PAPAL PLANE (Reuters) - Pope Francis on Sunday advised U.S. Catholics who feel they are torn between two imperfect candidates for president to study and pray before they vote and to make sure to follow their conscience.

During his traditional, freewheeling in-flight news conference with reporters on the plane returning from Azerbaijan, Francis was asked how he would counsel American faithful and what wisdom they should keep in mind.

"You have asked me a question that describes a difficult choice because, according to you, there are difficulties with one and difficulties with the other," the pope said, without naming Democrat Hillary Clinton or Republican Donald Trump.

In posing the question, the reporter made allusions to Clinton's support of abortion and Trump's statements vilifying migrants and religious minorities.

"During political campaigns, I never say a word," the pope said. "The people are sovereign. I would only say, study the proposals well, pray and choose with your conscience."

But in the rest of his response, while stressing that he wanted to talk about a "fictional situation," Francis appeared to be saying that the United States was among the countries that had become so politicized that it had effectively lost what he called a culture of politics.

"When in any country there are two, three or four candidates who don't satisfy everyone, it means that perhaps the political life of that country has become too politicized and that it does not have much political culture," he said.

"People say 'I'm from this party' or 'I'm from that party,' but effectively, they don't have clear thoughts about the basics, about proposals," he said.

Last February, while returning from Mexico, the pope was asked if U.S. Catholics could vote for someone with Trump's views on immigration, particularly on the candidate's promise to build a wall at the border with Mexico.

He said a person with such views was "not Christian."

Trump struck back, calling the pope's comments "disgraceful."

(Reporting by Philip Pullella; Editing by Lisa Von Ahn)