What you notice, approaching Fourth Presbyterian Church in Bethesda on a Sunday morning, are the cars. They stretch along River Road -- the wide, tree-lined boulevard in front of the imposing brick church -- as far as the eye can see. They fill the 300-space parking lot. They are double-parked in the lot of Kenwood Country Club across the street.

Their passengers have come from all over the Washington suburbs to worship in one of the area's fastest-growing evangelical churches, passing mainline Protestant and Roman Catholic churches whose parking lots are half full. It is a dramatic change from three years ago, when Fourth Church and its dwindling membership were nearing the end of their association with the mainline Presbyterian Church.

A total of 2,000 people now attend Fourth Church's three Sunday services. These parishioners, new and old, young professionals and influential Washington policymakers, are part of a demographic sea change in American churches that has little to do with the rise and fall of television evangelism.

In the last two decades, many middle-class Americans have left mainline churches, with their emphasis on social programs, and joined the evangelical movement, attracted by a more inward-looking faith and clearer, stricter instruction in moral values. As many as one-third of Americans call themselves evangelical, according to pollster George Gallup Jr., himself an evangelical.

A handful of mainstream Protestant leaders first recognized this trend about 10 years ago. They included Dean M. Kelley, staff member of the mainline National Council of Churches, who wrote a book in 1977 entitled "Why Conservative Churches Are Growing." But, according to Kelley and others, it is only within the last year that the mainline churches have started considering evangelicals a serious threat.

Not all evangelicals have left the mainstream; if broadly defined as "born-again" Christians who take their religion seriously, they can be found in almost all Protestant denominations and some Catholic churches.

But most are found in congregations like Fourth's, which left the mainline Presbyterian Church-USA in late 1986 after years of growing dissatisfaction with its politics, both secular and denominational.

Most of Fourth's members came to feel that the mainline organization had departed from a cherished evangelical position: the Bible as the infallible word of God and thus the ultimate authority for life and for entry into heaven.

Increasingly, they voiced their displeasure, displaying the fervor of those who believe they have been "born again" through a renewed commitment to Jesus Christ and who want to share their faith as evangels, or messengers of good news. This fervor, Kelley said in his book, stems from "an assurance, a conviction of rightness, of being on the side of God, that most people in most human endeavors cannot match."

Such confidence also was behind Fourth's growth. Today, it offers as many as 21 Sunday School classes at two of its three Sunday worship services; from two to 10 programs each week night; a Teen Breakfast Club that draws a couple of hundred teen-agers every Thursday at 6:30 a.m.; a single adult's club of almost 500, and an extensive counseling program using paid and volunteer staff. This summer, it is running Backyard Bible School classes for children in as many as 30 neighborhoods around the Beltway.

Fourth's evolution into a mainstream Washington institution, and then into an evangelical force, began in 1958 when it moved from 13th and Fairmount streets in Northwest to River Road in Montgomery County. Its membership had dwindled to about 600, and the Rev. Richard Halverson drew on burgeoning suburban growth to recruit new parishioners from various Christian denominations.

As a preacher, the genial, broad-faced Halverson played to his congregation as he had played to his audience when he was a teen-aged vaudeville singer and a young Hollywood actor. He spoke, parishioner Paul Arveson says, "as if he were in dialogue with you. He knew how you could interpret what he was saying, and he would anticipate your questions."

Former parishioner Al Hedrich recalls Halverson's tenure, which ended seven years ago, as "a golden period" in which membership tripled. Like their evangelical counterparts in burgeoning suburbs across America, Halverson's parishioners recruited members at work and in neighborhood homes. They spoke a simple message focused on the Bible rather than on a particular religious tradition, and it struck a chord with new suburban families searching for stability and assurance.

As Fourth's congregation grew, it diversified. Its increasingly fractious moderate and conservative factions were held together by Halverson's inclination to negotiate rather than confront.

Hedrich, a telecommunications engineer who joined Fourth in the early 1960s, recalls that as a church officer about 10 years ago, he was criticized by some parishioners for distributing more readable "Living Bibles" to church school students instead of the King James version. But Halverson supported him. When Hedrich's daughter became interested in becoming a minister, Halverson supported that too, though many in his congregation objected to women as pastors.

When Halverson resigned in 1980 to become chaplain of the U.S. Senate, the 24 laymen who comprised Fourth's board of elders ran the church for the next three years, seeking the right replacement for him and struggling with the church's widening rift with the Presbyterian Church-USA.

In the eyes of Fourth's leaders, the denomination had become too worldly, adding eight creeds of belief to the Westminster Confession, which professed biblical infallibility. Also, it had taken a pro-choice position on abortion and supported giving sanctuary to illegal aliens.

Moreover, it required member churches to consider female applicants when selecting pastors and assistant pastors. Fourth Church declined, its elders citing passages from the New Testament they said dictated male leadership only. The Rev. Ed White, chief executive of the 115 mainline Presbyterian churches in the Washington area, remembers that Fourth representatives back then rarely attended the governing body's meetings.

"It was no longer a family debate," Fourth elder John Birnbaum explained. "We were two separate families." This troubled period was reflected in Fourth's Sunday attendance, which dropped by almost half.

In 1984, after a long and difficult search for Halverson's successor, the elders chose the Rev. Robert Norris, a 36-year-old Welshman from the large, prestigious Hollywood Presbyterian Church in California. They were impressed by his two doctoral degrees from St. Andrews University in Scotland, important to Fourth's well-educated congregration, and appreciated his love for preaching, crucial to Fourth's reputation for an energetic pulpit ministry.

Norris shared the elders' belief in a strict interpretation of the scriptures, and he was willing to lead the congregation into a new association with the Evangelical Presbyterian Church. The denomination, which originated in 1981 with 12 churches, has grown to 100 churches, most of which have switched from the mainstream church.

At the group's annual meeting in Atlanta recently, Norris was the keynote speaker, signaling his status as a rising star in the evangelical movement. Under his ministry, which emphasizes, he says, a conservative, personal gospel, Fourth's attendance has swelled again.

Many newcomers are like Lynn Page, 32, and her husband, David, 34, residents of upper Montgomery County who joined Fourth two years ago after searching almost a year for a church. They chose it, they said, because their literal interpretation of the Bible is at the heart of their religious life and because Fourth's extensive education program indicates that it is "serious about its faith."

The Pages believe it is appropriate to try to influence public policy issues that, David Page says, "have a clear black and white in the Bible." In their view, the Bible prohibits abortion, euthanasia and homosexuality. Lynn Page, editor of the newsletter Right to Life Maryland News, is organizing a committee at Fourth to oppose abortion.

The Pages are more conservative than many of Fourth's longtime members, including Arveson, 43, a Navy research physicist in Rockville who was "born again" 24 years ago as a college sophomore and has attended Fourth for 10 years. He and his wife, Kathy, whom he met at a church singles group, have considered other churches, but found other evangelical churches too closed-minded and mainstream churches "too pluralistic . . . anything goes."

After starting an association of professionals, the C.S. Lewis Institute, to help further his intellectual exploration of the Bible, Arveson has come to see scripture as "theological doctrine, not scientific fact," a position that sets him apart from some of his fellow parishioners.

Other liberal parishioners have left over the years, including Al Hedrich.

"I was hurt and surprised when these people took a personal dislike to me because we differed on something," said Hedrich, who, with his wife, Maxine, transferred to the mainline National Presbyterian Church in the District two years ago.

"We saw a drift to the reactionary," Maxine Hedrich said.

Norris acknowledges that he has attracted "a more conservative element" to the church, but says he would like to keep the moderates. His colleagues in other evangelical pulpits are engaged in the same struggle, which they say could determine whether evangelicalism continues to claim a significant number of American Christians.

"You're always balancing what is care and what is capitulation," Norris said.

Education programs -- better known as Sunday School -- form the heart of Norris's ministry. They are highly structured. Adults are expected to do at least a half hour's homework each night during the week, often studying the scriptural view of current secular issues. Children as young as 2 follow lesson plans.

Less attention has been paid to programs for the wider community. Fourth Church spends about 15 percent of its approximate $2 million budget on domestic social projects, according to church officials, a typical proportion for some suburban churches but far less than a number of urban evangelical churches spend.

Norris is aware that his strict-constructionist interpretation of the Bible, as it relates to church policy, does not have universal support. He said he has been called "a living dinosaur" because he believes that church leaders should not be divorced, a view that led him to dismiss a popular choir director who was seeking a divorce.

Some parishioners also have been disturbed by his statements that women should not be on the church's board of elders. They fear that his position -- though it contradicts church policy -- may persuade the congregation to elect only men to the board, which now has two women.

They will soon see whether there is any basis for those fears. More than half of the elders are up for election by the congregation within the next 18 months, elder Birnbaum said, and "the direction of the church is in the balance."