VATICAN CITY (Reuters) - Pope Francis has ordered a review aimed at simplifying the Church's procedures for annulments, the Vatican said on Saturday, a move that could make it easier for Catholics to end marriages.

A statement said Francis had appointed an 11-member commission of canon lawyers and theologians to propose reform of the process, "seeking to simplify and streamline it while safeguarding the principle of the indissolubility of marriage".

An annulment, formally known as a "decree of nullity," is a ruling that a marriage was not valid in the first place according to Church law because certain pre-requisites, such as free will, psychological maturity and openness to having children, were lacking.

In the past decades many within the 1.2 billion-member Church have complained that the procedure is too complicated and archaic.

Most annulments take place at the local diocesan level. Each decision must be reviewed by a second tribunal, a step reformers say is superfluous and should be eliminated.

The Church does not recognize divorce. Catholics who divorce and re-marry outside the Church are considered to be still married to their first spouse and living in a state of sin, which bars them from receiving sacraments such as communion.

The situation of divorced and remarried Catholics who want to fully participate in the Church is a topic of great debate, particularly in countries such as the United States and Germany, and will be a main theme at a synod of bishops from around the world at the Vatican next month.

Progressive bishops have said the Church should be more merciful with people with failed first marriages even if they have not been annulled and Francis has indicated he is open to change.

Francis demonstrated this openness last week when he married 20 couples, some of whom had already lived together and had children. He led each pair through their vows one by one at St. Peter's Basilica in the Vatican.

(Reporting By Philip Pullella)