A disappointingly meager interdenominational congregation gathered at the Metropolitan Memorial United Methodist Church here last Sunday afternoon for the Washington area's first ecumenical communion service sponsored by the Consultation of Church Union.

The gathering of fewer than 150 persons - of whom about a third were members of the clergy, their spouses or choir members - represents the latest ripple from the splash 17 years age of the boulder hurled into the stream of Christianity in this country by the Bishop James A. Pike.

It was in 1960 that the iconoclastic Bishop Pike, speaking from the pulpit of his San Francisco cathedral to a congregation full of reporters in town for another church meeting, proposed that major Protestant denominations should unite into one church.

The idea. So innocuous-sounding today, was a startling proposition then. But it was clearly an idea whose time had come. Within a matter of months, both the thinkers and the power-brokers of half a dozen (later expanded to 10) of the nation's most prestigious Protestant denominations had come together and wrestled the idea into an institution dubbed Consultation on Church Union - COCU for short.

In the early years of COCU, thousands of some of the churches' most expensive man-hours went into hammering out detailed plans to merge churches of diverse traditions into one massive denomination of perhaps 25 million members. Early COCU meetings were media events.

Then came Vatican II and the massive changes in the Catholic Church involving new and even more startling ecumenical possibilities.

At about the same time, involvement by the COCU member-churches is civil rights and antiwar movements distracted both attention and resources from COCU. In not a few denominations, hostility of some members to church involvement in social and political issues spilled over into antagonism toward ecumenical endeavors as well.

In recent years, internal church differences over the role of women and homosexuals, liturgical renewal and a growing liberal-conservative theological polarization has preoccupied some COCU member churches.

In addition, ecumenical ventures themselves over the past decade have tended more and more to be more task-oriented: in a given situation, a group of churches or church organizations come together to accomplish one specific task with little thought for long range agreement on fine theological points. Projects have ranged from short-term drives for famine relief to the mobolizing of resources from several denominations to form a new jointly supported congregation.

It was partly to rescue COCU from the shadows into which it has been pusged by these and other trends that its supporters came up with the plan for Interim Eucharistic Fellowships, of which last Sunday's gathering was the first attempt in this area.

Since the eucharist is the core of Christian worship, the fellowships were conceived with the idea of bringing Christians of varying traditions together periodically - two or three times a year at most - to receive holy communion together.

In his communion meditation Sunday, Rev. John E. Brandon, COCU's associate general secretary, told the worshipers that "Christians receive the eucharist as an event rich in meaning for their lives."

He reviewed the varied ways different Christian traditions understand the eucharist - "as a memorial . . . as a sacrament . . . as communion . . . as Christ's presence . . as the eucharist" which he defined as the Greek word for thanksgiving.

"Holy communion," he added, "offer us fellowship with God," but warned: "Mockery is made of the eucharist when separations of the world are allowed to enter into church life."

Interviewed after the service, Brandon said that "about 100" other communities in the United States are in the process of developing similar eucharistic fellowships, and that 12 of them already have held services.

The Rev. G. David Shreeves, pastor of Shepherd Park Christian Church and coordinator of planning for the local fellowship, admitted his disappointment with the meager attendance, but expressed the belief that "it will grow."

He added, however, "I dont think it will be large at any time . . . I don't think it will shake the world but I think it will stay alive."

The local planning committee he said, will meet after Thanksgiving to evaluated last Sunday's session and make plans for future gatherings. "The whole thing is ipen, flexible," he said.

Neither Shreeves nor Brandon gave any credence to the judgement of some contemporary church leaders that the once bright promise of COCU, after 17 years, is dead.

On the contrary, Brandon observed, "I see emerging newness in the consultat ion.