BARRING a last-minute intervention by the Holy Spirit, the American Episcopal Church will commit aesthetic bara-kiri in Denver this month when its general convention consigns to the ashcan of history the beloved 1928 version of the Book of Common Prayer.

The Book of Common Prayer is not the exclusive property of the 65-million-member Anglican Communion. It is a thing beyond cant or dogma, comprising -- with the King James translation of the Bible, the works of Shakespeare and those of Milton -- one of the four great arches that support the vaulted ceiling of the English language.

To tinker with what G. K. Chesterton called "the masterpiece of Protestantism" was a deed of monumental ecclesiastical folly and barefaced literary impertinence. Predictably, those who had the temerity to do so have come up, after six revisions, with a substitute that is twice as long and half as satisfying.

The revisionists have succeeded in making the beautiful banal, in substituting a 1,001-page mundane mishmash for that which was majestic and monumental. In place of the stately 16th century cadences of Archbishop Thomas Cranmer, we are offered parsonprattle and committeespeak.

The Episcopal Church already has begun to pay the price for this act of clerical vandalism. Church membership has declined from a 1967 high of 3.4 million to 2.9 million in 1975, with, the final loss to the church likely to be on the order of a third of its communicants. With the printing costs of the new verson and its five predecessors likely to exceed $36 million, there has been a significant decline in annual giving.

The irony is that there never was and is not now among the "all sorts and conditions of men" who constitute the laity a groundswell for revision. Last month, a Gallup poll of Episcopalians showed nearly three out of four lay members preferring the 1928 book, while 80 percent of the clergy (who number only 8,200) went on record as favoring the tin-eared newer version.

In fairness to the Standing Liturgical Committee, not all the decline in membership or the fall in revenue can be blamed on it. Paying off the Black Panthers, ordaining women and edging toward the ordination of homosexuals had not exactly endeared the church's leadership to its members. To many, the management of the Episcopal Church seemed to owe as much to Chrysler as to Christ.

But these dispensations, important as some of them were theologically (the ordination of women damaged ecumenical relations with the Eastern Orthodox and Roman Catholic churches), were peripheral to the life and worship of the man in the pew. Taking a semantic butcher knife to the Book of Common Prayer was not.

What happened was that, in their effort to be trendier than thou, the revisionists sought to make the prayer book appealing to the lowest common denominator rather than leaving its language to move men toward God.

"Thees" and "thous," for instance, are consigned to the outer darkness, charged with interposing a distance between man and his God. But surely there is, must be, such a distance: While one may acknowledge the Lord as one's shepherd, it is presumptuous to claim Him as, in CB jargon, one's good buddy.

Clearly the Standing Liturgical Committee contains more priests than poets: The revisions in many instances have destroyed the meter of some of the world's loftiest language, substituting for it that which is tasteless, bland and condescending. It is as if someone were trying to play a Bach cantata on the harmonica.

C. S. Lewis once described the 1928 Book of Common Prayer as shining "with a white light hardly surpassed." Those Episcopalians determined that this light shall not be forever extinguished at Denver this month plan to press for a dispensation retaining the old liturgy as an alternative authorized version available for use by parishes that so desire it.

Their chances, however, do not appear good. The revisionists maintain that to do so would be to perpetuate unhappiness, confusion and polarization, conveniently forgetting that it is their work that has created this unhappiness, confusion and polarization.

The revisionists have the votes -- only 371 of the 742 members of the House of Deputies are lay members -- and, as they have shown since they took over the General Convention in Minneapolis in 1976, they are quite prepared to use this power to impose upon their protesting brothers in Christ a liturgy that literary critic Cleanth Brooks has described as "pedestrian, second-rate, banal."

That is why it will take a miracle in Denver to preserve for generations yet unborn one of the loveliest jewels in the crown of Anglicanism, an outward and visible sign of an inward and spirtual grace. But miracles do happen.

Venite, Spiritus Sanctus .