A Vatican document on the theology of liberation to be published officially today says that service to the poor, both through charity and by working to change oppressive political and economic structures, must be a priority for Christians and that in "the extreme case," armed struggle may be justified "as a last resort."

The 59-page "Instruction on Christian Freedom and Liberation" counsels "passive resistance" rather than violence and revolution to achieve these ends.

But "to put an end to an obvious and prolonged tyranny, which is gravely damaging the fundamental rights of individuals and the common good," the document says, armed struggle is permissible. It offers moral guidelines for such conflicts that are roughly analogous to the church's traditional criteria for a just war.

While asserting that "situations of grave injustice require the courage to make far-reaching reforms," the document warns against resorting to "the myth of revolution," which could lead to "the setting up of totalitarian regimes. The fight against injustice is meaningless unless it is waged with a view to establishing a new social and political order in conformity with the demands of justice."

The church's "essential mission," that of "evangelization and salvation," cannot be separated from a concern for the problems of the daily lives of people, the document says. "The church desires the good of man in all his dimensions, first of all as a member of the city of God, and then as a member of the earthly city."

The document states that it is "perfectly legitimate that those who suffer oppression on the part of the wealthy or the politically powerful should take action, through morally licit means, in order to secure structures and institutions in which their rights will be truly respected."

Issued by the Vatican Congregation for the Doctrine of the Faith and signed by Cardinal Joseph Ratzinger, who heads it, the document was to be made public at the Vatican today although texts were distributed with an embargo. Several news organizations broke the embargo, which then dissolved.

The document makes no reference to specific countries or individuals. Neither does it specifically cite political systems, although it condemns shortcomings of both capitalism and Marxism.

Liberation theology, developed by priests working with the poorest of Latin America's poor, holds that the Gospel requires the church to take responsibility for changing social, economic or political conditions that deprive people's dignity.

An earlier document, also by Ratzinger, in September 1984, sharply criticized the "deviations" from traditional Christian doctrine made by some liberation theologians in their use of Marxist social and economic analysis, including the concept of class struggle.

The Vatican promised it would balance the 1984 document with a more "positive" look at the movement, which has spread to Africa and Asia. The new document, a summary of which has been sent to bishops throughout the world, takes a markedly up-beat look at the phenomenon.

Liberation theology's concept of a "preferential option for the poor" is embraced by the new instruction. "Those who are oppressed by poverty are the objects of a love of preference on the part of the church, which since her origin and in spite of the failings of many of her members has not ceased to work for their relief, defense and liberation," the document says.

A key development of liberation theology, the structuring of "base communities," or cells of Christians who come together for mutual support, is viewed in the Vatican document as "a source of great hope for the church . . . if they really live in unity with the local church and the universal church."

But the document rules out the involvement of clergy in secular politics -- one of several bones of contention with priests who have supported the Sandinista revolution in Nicaragua.

"It is not for the pastors of the church to intervene directly in the political construction and organization of social life," the document says. "This task forms part of the vocation of the laity acting on their own initiative with their fellow citizens."

This position reflects the views of Pope John Paul II, who has given his approval to the document, and is a mild rebuke of Philippine Cardinal Jaime Sin, church observers say, for his role in the overthrow of ex-president Ferdinand Marcos.

The document warns that Christians "cannot passively accept, still less actively support, groups which by force or by the manipulation of public opinion take over the state apparatus and unjustly impose on the collectivity an imported ideology contrary to the culture of the people."

Armed struggle is recognized "as a last resort to put an end to an obvious and prolonged tyranny which is gravely damaging the fundamental rights of individuals and the common good."

But "passive resistance" is favored over violence because it is "more conformable to moral principles" and just as likely to succeed.

"One can never approve, whether perpetrated by established power or insurgents, crimes such as reprisals against the general population, torture, or methods of terrorism and deliberate provocation aimed at causing deaths during popular demonstrations.

"Equally unacceptable are detestable smear campaigns capable of destroying a person psychologically or morally," the instruction says.

The document condemns "systematic recourse to violence put forward as the necessary path to liberation." It adds: "One must condemn with equal vigor violence exercised by the powerful against the poor, arbitrary action by the police, and any form of violence established as a system of government."