Garnell Stuart Copeland was 13 when he startled San Francisco's virtuoso organist Newton Pashley by repeating from memory the Bach tocata that Pashley had just finished. Copeland was 26 when he became the organist and choirmaster at the Church of the Epiphany in downtown Washington.

Copeland was just 34 when he died in an ambulance after being attacked by three assailants on the steps of his Capitol Hill home on Jan. 6, 1977. His attackers have never been identified.

Last Sunday, the congregation of the Episcopal church dedicated in Copeland's name one of two particularly fitting memorials, a horizontal rank of 49 pipes, for the large Aeolian-Skinner organ Copeland helped design.

The other memorial, a stained-glass window incorporating the notation of a motif from a Copeland composition, will be dedicated Jan. 7 along with five other new windows in the church.

"Garnell was a highly vivacious, colorful, lovable person-a personality as well as a musician," recalled the Rev. Dr. Edgar Romig, rector of Epiphany.

At the Sunday morning service, a crowd of 300 heard for the first time the trompette-en-chamade mounted over the balcony at the rear of the church. With the addition of the new stop, which cost approximately $10,000, Epiphany may be the first parish church in the United States with two such ranks, one in each end of the building.

About 400 persons gathered for the Evensong service, preceded by a recital by Boston organist Leo Abbott, which included music written for the occasion by Copeland's successor at Epiphany, Charles Callahan.

The trompette-en-chamade is actually the second addition to the organ bought in Copeland's memory. The first, an eight-foot Spitz-Principal, was installed last year. The next addition in Copeland's name will be a Solo Division to be placed in the old organ chamber. Altogether, some $20,000 has been raised for memorials to Copeland's memory.

Copeland was a dramatic performer who loved the power and flourish of the pipes; for some years he regularly demonstrated the pipe organ at the Kennedy Center for tourists and often performed there. His annual concerts at First Presbyterian Church in Oakland, Ca., drew increasingly large audiences. He had also appeared at Riverside and St. Thomas churches in New York and in Lincoln Center.

According to Romig, Copeland was a student at the College of Church Musicians at Washington Cathedral when he was sent in 1966 to Epiphany to substitute for the ailing organist, Adolf Torovsky, who had served the church nearly half a century. Copeland stayed on as an assistant, giving the dedicatory recital on the then-52-rank Aeolian-Skinner, and became organist-choirmaster in July 1968.

The night of his death, Copeland was returning from the evening service of the Feast of Lights. Six weeks later, a memorial concert at the Kennedy Center drew 2,000 friends and admirers.

The stained-glass window, which is high above and to the left of the altar, is one of a series of six depicting the days of Creation.

The price of the new pipes was partly raised through sales of an album of Copeland recordings, a collection that includes the same Bach toccata which so impressed Pashley. In the liner notes, Romig recalls that Copeland particularly revered Bach and played his works "buoyantly and passionately-convinced that Bach, a buoyant and passionate person himself, would approve." To his friends at Epiphany, that seems an appropriate description of Copeland as well.