ROME (Reuters) - Pope Francis on Monday said he believed that Roman Catholic priests should be celibate but the rule was not an unchangeable dogma, and "the door is always open" to change.

Francis made similar comments when he was archbishop of Buenos Aires but his remarks to reporters on a plane returning from a Middle East trip were the first he has made since becoming pope.

"Celibacy is not a dogma," he said in answer to a question about whether the Catholic Church could some day allow priests to marry as they can in some other Christian Churches.

"It is a rule of life that I appreciate very much and I think it is a gift for the Church but since it is not a dogma, the door is always open," he said.

The Church teaches that a priest should dedicate himself totally to his vocation, essentially taking the Church as his spouse, in order to help fulfill its mission.

However while priestly celibacy is a tradition going back around 1,000 years, it is not considered dogma, or an unchangeable piece of Church teaching.

There has been pressure for change, particularly in the wake of recent sexual abuse scandals with proponents of optional celibacy in the Church arguing that sexual frustrations could drive some priests to sexually abuse children.

But the Church has rejected this argument, saying that paedophilia, whether in the Church or outside of it, is carried out by people with psychological problems.

Priests are allowed to marry in the Anglican and other Protestant churches as well as in the Orthodox Church.

(Reporting by Philip Pullella; Editing by Eric Walsh)