Early one morning next month, as the first rays of California sun glint off the plastic castles and mountains of nearby Disneyland, more than 200 bishops of the Episcopal Church will assemble in Anaheim for a solemn conclave that will influence the course of their church into the 21st century.

The bishops, carefully sequestered from the rest of the denomination's triennial General Convention that begins its eight-day meeting at the Anaheim Convention Center next Saturday, will elect the church's next presiding bishop.

Choosing a successor to Bishop John Maury Allin is the most important of many issues before the bicameral governing body of the 2.8 million-member denomination. The presiding bishop serves a 12-year term.

Even though the powers of the presiding bishop in the democratically structured church are constitutionally defined as chief administrator and executive officer, his influence can be crucial in setting the direction for the church and the implementation of General Convention decisions.

Allin, elected in 1973, openly opposed the ordination of women to the priesthood. Even when the 1976 General Convention voted for it, Allin proposed a "conscience clause" that would exempt bishops who, in conscience, opposed women priests from administering the rite.

There has been some discussion in the House of Bishops of asking the Anaheim convention to rescind this conscience clause, to put the church unequivocally in favor of ordaining women.

Despite his personal position, Allin, as chief executive for the church, has helped women postulants whose bishops have turned them down on grounds of conscience to find another bishop to ordain them.

Allin's predecessor, Bishop John E. Hines, was an activist, leading his denomination into the thick of the civil rights struggles, changing forever the church's WASPish image. But many disgruntled Episcopalians stopped giving and stopped coming. Manyjoined the movements that splintered off after the 1976 decision on women priests and the revision of the Book of Common Prayer, citing the church's social activism in the racial struggles of the '60s as another reason for leaving the Episcopal Church.

The church, like most mainline Protestant denominations, sustained a net loss of more than 500,000 members from its 1966 peak to the beginning of this decade, with "no significant change in membership" in the past year, according to church reports.

Under Allin's tenure, during which he has emphasized reconciliation, activists in the church such as the Urban Bishops' Caucus and the Episcopal Urban Caucus have chafed at his conservative leadership, hoping for a more liberal successor.

This year for the first time in the 200-year-old U.S. Episcopal Church, priests and lay persons have had a part in choosing the presiding bishop. Two years ago, a 27-member committee began a study of the needs of the church and a lengthy series of interviews to come up with a field of four candidates.

They are Bishop John T. Walker of Washington, Bishop Edmond Lee Browning of Hawaii; Bishop William C. Frey of Colorado; and Bishop Furman Charles Stough of Alabama. Other candidates could be nominated from the floor of the House of Bishops on the day before the election, but that is generally considered unlikely.

After the bishops make their choice of the next presiding bishop on Sept. 10, they must remain sequestered until the House of Deputies -- some 1,000 priests and lay people meeting across town at the convention center -- has ratified the election.

Other issues before the convention will include the election of a new president and vice president of the House of Deputies. One of the nominees for the latter post is Pamela Chinnis of Arlington, who is also a member of the national church's Executive Council.

The General Convention will be asked to explore the possibility of moving the national church out of its New York City headquarters, a few blocks from the United Nations. Washington, D.C. and Indianapolis are among the sites that have been discussed.

The church's commission on Human Affairs and Health has recommended no change in the church's position on abortion, adopted in 1967, which endorses termination of pregnancy in case of rape or incest, a threat to the mother's health or the likelihood of a "badly deformed" baby.

But antiabortion forces have indicated they will fight, as they did at the Presbyterian Church Synod last spring, to toughen the church's stance.