By Philip Pullella

VATICAN CITY (Reuters) - Pope Francis called on Tuesday for a radical change of attitude towards immigrants, saying they should be welcomed with dignity and denouncing the "populist rhetoric" he said was fuelling fear and selfishness in rich countries.

The pope, who has championed the cause of migrants since taking office in 2013, did not single out any country for criticism.

But his words may resonate in the United States, where courts have blocked an executive order by President Donald Trump to suspend arrivals from seven mainly Muslim countries, and in a Europe still struggling with a mass influx of more than 1.3 million migrants and refugees since the start of 2015.

Immigrants should not be rejected out of hand as unworthy rivals but given a "responsible and dignified welcome," particularly those fleeing war, the pontiff said in a lengthy address to participants of a conference on migration in Rome.

"Faced with this kind of rejection, rooted ultimately in self-centeredness and amplified by populist rhetoric, what is needed is a change of attitude, to overcome indifference and to counter fears with a generous approach of welcoming those who knock at our doors."

Populist anti-immigrant parties have made gains in a number of European countries, including Italy, France and the Netherlands, where anti-Muslim politician Geert Wilders on Saturday launched his campaign for next month's election with a promise to crack down on "Moroccan scum".

"For those who flee conflicts and terrible persecutions, often trapped within the grip of criminal organizations who have no scruples, we need to open accessible and secure humanitarian channels," the pope said.

Countries had a "moral imperative" to help exiles, asylum seekers, migrant workers, victims of human trafficking and even migrants in "irregular situations," he added in an apparent reference to undocumented immigrants.

A number of U.S. cities have filed law suits challenging Trump's executive order directing the federal government to withhold money from cities that have adopted sanctuary policies toward such people.

Francis even echoed the U.S. Declaration of Independence by saying they all had "inalienable rights".

"Defending their inalienable rights, ensuring their fundamental freedoms and respecting their dignity are duties from which no one can be exempted," he said.

(Reporting by Philip Pullella; Editing by Mark Trevelyan)