The presiding bishop of the Episcopal Church, in a farewell address following his 12-year term, said today that the Reagan administration's preoccupation with national security has given the United States an image as a bully in many parts of the world.

Addressing the opening session of the church's triennial general convention here, Presiding Bishop John Maury Allin charged that in recent years, national security "is declared to be for human benefit while actually being a source of threat. The more that is demanded for its support results in less security and additional needs."

Not only are current policies failing to provide real security, he said, but they have created "cynicism and despair" among people in other parts of the world.

"The sad truth is that the American image of a great democratic republic and generous good neighbor has become overshadowed in the sight of many . . . by the image of a bully, preoccupied with profits and self-protection," he said.

Citizens in many small countries view the United States as equal to the Soviet Union as exporters of arms, manipulators of world markets and resources and inhibitors of fair trade with Third World nations, he said.

Throughout his tenure as presiding bishop, Allin has assumed a low profile on secular issues and most church issues while following what he characterized as a policy of "reconciliation."

Allin said today that he believes President Reagan "is a good man," but that "he does not have an adequately detailed or in-depth comprehension of the human predicament, the causes and effects of human suffering in the world."

It is time, he continued, to say to the president "that it is now of crucial importance that we lower the volume of our ideological rhetoric and that we listen carefully to the representative voices from around the world, especially the suffering, the oppressed and the poor."

Allin also used his farewell speech to speak his mind on several church questions.

He called on clergy who divorce then remarry to leave the priesthood and "continue faithfully in a valid form of lay ministry." Divorced clergy cannot "substitute a second spouse in the church's community in which they serve with the assumption that there is no harm, loss or damage to the community."