In a display of religious pagentry not seen before outside of England, the heads of the worldwide Anglican Communion yesterday began a five-day conclave here with a colorful and solemn evensong service at the Washington Cathedral.

The 27 primates, as heads of Anglican provinces are called, are meeting in closed-door sessions at the cathedral's College of Preachers this week to exchange information and to examine issues such as priestly authority, world poverty and relations with other churches. The gathering here marks the first time the group has met outside England.

At the climax of yesterday's service the churchmen, most of them garbed in crimson robes over starched white surplices, proceeded to the great high altar of the cathedral and gathered around the archbishop of Canterbury to pray for guidance for their deliberations, for world peace and for the church.

A near-capacity crowd of Episcopalians and members of other churches crowded the cathedral to join the worship.

Because of the presence of Vice President and Mrs. George Bush the cathedral was under security. Some worshipers who wanted to take photographs of the historic occasion had to demonstrate to Secret Service agents at the doorways that their cameras were not weapons.

The churchmen are of every race, from every continent, many of them the spiritual descendants of the missionaries that accompanied British colonialism of the 18th and 19th centuries. The once-proud boast that the sun never sets on the British Empire can now be applied more accurately to the Anglican Communion to which 64 million people worldwide give allegiance.

In his sermon yesterday Washington Bishop John T. Walker expressed the hope that the gathering of churchmen of such diverse backgrounds "can be a sign of unity of all God's people. . . ."

"We continue to yearn for unity," said Walker, who is serving as chaplain as well as host for the meeting of primates. "Perhaps the greatest tragedy of mankind is that the more we yearn for unity the more we seem to be divided." o

Yesterday morning, many of the visiting primates preached at area churches. At the cathedral itself, the Most Rev. Robert Runcie, the 102nd archbishop of Canterbury, praised the successful launch of the American space shuttle as a technological triumph. He pointed out that the communication advances that can come out of such technology "could be an important contribution to increasing . . . mutual understanding in the world and to thwarting the ambitions of those rulers who would keep their countries isolated from the rest of mankind."

But he deplored the fact that moral progress in the world has not kept pace with technological advance. "There is a terrifying disparity between our technical achievements and our moral progress," he said.Along with the exploration of outer space, "We need an energetic program of exploration of inner space which harbors the fears and the desire to dominate, which are the sources of the violence and the divisions which disfigure the world."