LONDON — The leader of the Church of England appealed for harmony among the faithful as it went into a vote Tuesday on whether to allow women to serve as bishops, a historic decision that comes after decades of debate.

The push to muster a two-thirds majority among lay members of the General Synod is expected to be close, with many on both sides unsatisfied with a compromise proposal to accommodate individual parishes which spurn female bishops.

In a sermon at a communion service before the debate, Rowan Williams, the archbishop of Canterbury, quoted Cardinal John Henry Newman's motto, "heart speaks to heart."