Queen Elizabeth II will speak perhaps the most controversial words of her reign Wednesday when she joins ministers of the Church of England in holy communion to open the third general synod of the Anglican Church.

Led by the archbishop of Canterbury, the communicants in Westminster Abbey will be reciting the service in the flat contemporary language of the church's new "Alternative Service Book," instead of in the familiar, flowery phrases of the three-century-old "Book of Common Prayer."

The 1,000-page compilation of church services, prayers and psalms in the 20th century vernacular will be formally published Monday, after a quarter century of liturgical research and revision by Anglican scholars. It has been hailed by church leaders as "a major event in the life of the Church of England."

But many angry Anglican clergy, lay leaders and parishioners are fighting determinedly against widespread use of the "Alternative Service Book," asserting it desecrates church traditions and the English language.

Some of the changes seem minor, although they can grate on an ear turned to the mellifluous phrases the 1662 "Book of Common Prayer" has kept alive.

In the Lord's Prayer, for example, "trespasses" becomes "sins" and the familiar opening, "Our Father, which art in heaven, hallowed by thy name," is replaced by "Our Father in heaven, hallowed be your name." The poetry of the prayer's ending, "for Thine is the kingdom, the power, and the glory, for ever and ever," may seem somehow diminished by its substitute: "for the kingdom, the power and the glory are Yours now and forever."

Other changes substitute the syncopated rhythm of pop and rock for the more measured medieval meter. In place of the traditional opening of the Te Deum, "We praise Thee, O God. We acknowledge Thee to be the Lord," parishioners chant, "You are God; we praise You. You are the Lord; we acclaim You."

More extensive and substantial alterations have been made in the marriage ceremony. In place of the traditional beginning, "Dearly beloved, we are gathered here in the sight of God and in the face of this congregation, to join together this man and this woman in holy matrimony," the new book intones: "We have come together in the presence of God to witness the marriage of. . . ."

The dramatic-sounding "Therefore if any man can show any just cause, why they may not lawfully be joined together, let him now speak, or else hereafter forever hold his peace" has been replaced by the merely informative: "But first I am required to ask anyone present who knows a reason why these persons may not lawfully marry, to declare it now."

More concretely, in keeping with modern views of sexual practice and equality, the purpose of marriage is no longer in the stern language of the "Book of Common Prayer" for the procreation of children" and "for a remedy against sin, and to avoid fornication: that such persons as have not the gift of continency might marry, and keep themselves undefiled members of Christ's body."

Instead, it states, men and women marry "that with delight and tenderness they may know each other in love, and, through the joy of their bodily union, may strengthen the union of their hearts and lives."

This kind of change appeared enlightened to many of the experts who reviewed the "Alternative Service Book" in the British press. But they generally panned the new book otherwise.

The modernization, concluded Canon D. W. Gundry, church correspondent of The Daily Telegraph, "has the merit of making obscure verses clearer but often at the expense of beauty."

Prof. David Martin, who teaches sociology at the London School of Economics, takes a much harsher view as spokesman for the 20,000-member Prayer Book Society. Crusading to keep the "Book of Common Prayer" as the text for all Anglican services, the society says polls and surveys it has taken show that a majority of Anglican parishioners agree.

"Worship demands heightened language," Martin contends. "This is lowered language."

Church leaders point out that the new book is intended to complement rather than replace the "Book of Common Prayer," which cannot be ousted formally from Anglican churches without an act of Parliament.

But, said Martin, "the most ominous sign is that theology colleges training the clergy of the future have almost completely switched over."

Martin also notes that the American Episcopal Church has officially replaced the "Book of Common Prayer" with its own book of modern language services. He blames the Washington-based International Consultation on English Texts for pushing this "bureaucratic liturgy" across the Atlantic.

Anglican church leaders who supervised the compilation of the modern language services contend that they are more faithful translations of the Hebrew and Latin originals. They also believe the contemporary language will be more understandable and comfortable for parishioners at a time of falling church attendence and dwindling home prayer services.

"Liturgy is not something that can be allowed to become fossilized, as it must relate to the society in which it is used," the bishop of Durham, the Right Rev. John Habgood, told reporters. He envisioned the book's being revised as often as every 15 years to keep pace with the evolution of language and new liturgical scholarship.

"People say we've spoiled the prayer book," added the dean of York, the Very Rev. Ronald Jasper, who led the litrugical commission that produced the "Alternative Service Book." "That is a downright lie. We have put something by its side. There's no question of the clergy bulldozing the congregation into accepting it."

But Martin and the other dissenters fear the "Book of Common Prayer" will be unknown to the next generation of worshipers after comforting so many generations before them.