In the past 40 years America's mainline Protestant churches have suffered a membership loss of one-third, and shrinkage continues, despite impressive efforts to shore up the churches.

In the same period, Baptists have strengthened in membership, and fundamentalist and Pentecostal churches have surged. Although an estimated one-third of America's Roman Catholics are non-churchgoers, the sheer numbers of Catholics continue to increase.

The problem (if it is a problem) is confined to the Protestant denominations that have been part of American history and culture since colonial times - Episcopalians, Lutherans, Methodists, and Presbyterians notable among them. Social commentators whom I respect suggest that their steady decline in membership signals the demise of denominational Christianity.

I disagree. There are explanations for the shrinkage, as well as an argument to be made that the remaining adherents of these traditions are faithful remnants with the will to prevail.

The sharp growth in churchgoing following World War II may simply have been a blip in religious enthusiasm, with current numbers being more sustainable. After the war, Americans became a nation on the move, less reluctant to switch denominations when a family moved from another town to another.

The mainline denominations' attempts to accommodate the social upheaval of the 1960s undoubtedly cost them some members fond of the "Old Time Religion" of strict interpretation and discipline, who transferred to fundamentalist and nondenominational churches.

Secularism, too, is sometimes suggested as prompting the decline of the mainstream denominations. But the nation's collective belief in God remains as strong as ever, and the growth of huge nondenominational megachurches demonstrates the perennial pull of religion in America.

Nor is the ecumenical movement to blame for the shrinkage. The movement for Christian unity relies on collaboration among existing churches. There is no alternative "ecumenical" church to woo members away from their traditional denominations.

I would argue that Episcopalians need Lutherans, and Presbyterians need Methodists, in the same way that a vital American society needs African-Americans, Hispanic-Americans, Asian-Americans and the other peoples who have enriched us with their cultures and traditions. The old Christian denominations are living repositories of our American civilization. Theirs are among the religious languages all of us speak and understand.

Much as we might find a common religious language convenient, it would perforce be artificial and sterile. I'm reminded of St. Peter's in the Vatican, where one priest hangs a sign on his confessional inviting sinners to confess in Esperanto, an ambitious artificial language devised to serve as a common bond among the world's peoples.

All I could wonder is how Esperanto's creators could have created a vocabulary large enough to convey the array of sins to which humankind is prone.

(David Yount's latest book is "Celebrating the Rest of Your Life: A Baby Boomer's Guide to Spirituality" (Augsburg). He answers readers at P.O. Box 2758, Woodbridge, VA 22195 and dyount(at)erols.com.)

SHNS