BOSTON — IN a New England Episcopal church, where a Thanksgiving cornucopia of pumpkins, squash, Indian corn, and apples bedeck an altar, the pastor opens the Sunday service with a sermon on overcoming self-destructive thinking. It lasts 14 minutes.
At a crowded Methodist church down the street, the sermon comes at the end of the hour: a commentary on maintaining gratitude in a materialistic culture. It spans 16 minutes.
Both services illustrate a trend that has quietly crept into American church life over the past 20 years: the shorter sermon.
Once the central message of scriptural teaching and spiritual authority in American mainline churches, the sermon is shrinking as churches adjust to new audiences. Twenty years ago, say scholars, the average sermon was 22 to 30 minutes. Today it runs 12 to 18 minutes.
The trend worries pastors and theologians who say the shorter sermon dilutes the worship of God and ''dumbs-down'' the spiritual education found in Scriptures - and is a sell-out to those using marketing techniques to make religion appealing to the masses.
On the other side are ministers and teachers who argue that the unchurched masses have moved increasingly from print to video culture and need to be approached differently. Long sermons will not save souls in a secular culture, they say.
''Sermons are getting shorter and shorter,'' says Gabriel Fackre of the Andover Newton Theological Academy in Newton, Mass. ''What kind of study and skills do you need to prepare a 12-minute sermon? It is disturbing to me as a teacher of theology.''
''It is my task to help our graduates communicate to the society as it is,'' counters Haydn Robinson of the Gordon Conwell seminary in Hamilton, Mass. ''I may wish for the old days. But that isn't the hand we've been dealt.''
New church-service techniques are proliferating. In the Willow Creek Church outside Chicago - one of the emerging trans-denominational ''megachurches'' that target baby boomers - the Sunday sermon has been replaced entirely. Instead, the service, sometimes 90 minutes long, holds a dramatic reenactment of an ethical parable - not necessarily from the Bible.
At the other end of the innovational chart is the ''express service'' for the busy believer - a sermon, music, hymns, liturgy, and fellowship, all in 30 minutes.
Sermon length varies widely. Southern churches tend toward longer sermons. Liberal and mainline churches have briefer messages than conservative and evangelical churches. Individual pastors may change from Sunday to Sunday: At Foundry United Methodist in Washington, where the Clintons attend, a recent sermon by the Rev. Philip Wogaman lasted 18 minutes. The sermon the following week was 10 minutes - with the extra time given to a musical tribute to Bach.
''The mainline churches are dropping in time more dramatically,'' says Michael Duduit, editor of Preaching magazine in Louisville, Ky., who feels that Episcopals and United Church of Christ are the briefest.
The cause for shorter sermons is often attributed to contemporary culture. Congregations press ministers for shorter, more entertaining services. Members and potential converts lack familiarity with Biblical ideas. The result is sermons that are not only shorter, but often lack theological content.
''The fact is, people are Biblically illiterate today,'' says theologian Marva Dawn, author of ''Reaching Out Without Dumbing Down.'' ''But instead of teaching, pastors offer therapeutic sermons that become so accessible that they don't have much content.''
Theologian David Wells, author of ''No Place for Truth,'' argues the essence of Christianity is being drained from many sermons. Older issues of meaning, salvation, the works of Christ Jesus, have given way to sermons about ''stress management.'' He says Americans today who ''live in such a less predictable and secure situation'' now prefer a sermon that is ''calming, rather than an exposition on ideas about truth.''
A 1989 university study of model Christian sermons showed that many do not refer to or use Biblical themes at all.
The deeper cause of the short sermon, scholars say, is the playing out of a crisis of spiritual authority that dates back at least to the turn of the century. The crisis became an open one during the upheavals of the 1960s. Congregations criticized the often bland and conformist style of the 1950s - and rejected the minister as an authority figure. The minister, as a result, shifted into a role as friend and counselor. Many seminaries even did away with teaching the art of preaching.
Today, most of these schools again teach preaching. But the content of traditional sermons has not truly recovered, say theologians. So much ground has been ceded to the forces of popularization that the distinctness of Christian thinking is in jeopardy, they say. Churches are happy to emphasize ''grace.'' But they ignore works. Dr. Fackre says the ''feel good'' approach has ''taken the struggle out of theology.''
Such struggle, he says, is what gave Christian theology its particular redemptive ''bite.''
''The content has become sub-Christian,'' says Dr. Dawn. ''Pastors today put together anecdotes and little stories. There's often no sense offered that this congregation is part of a universal idea, no sense of a great heritage, no sense that being a Christian really matters very much.''
Church historian Martin Marty says the more market-oriented alternative church will continue so long as the ''undumbed down but often not uplifting church community'' is not renewed.