One morning last week Mildred Clark walked into a public school classroom, plucked a well-thumbed King James Bible from her plastic shopping bag and taught Scripture to a roomful of fidgety fifth graders, just as she has since 1948. She opened by reading a poem she wrote entitled "Baby Moses," followed with a quiz on Biblical figures, and closed with the New Testament story of a miraculous healing performed by an apostle of Christ.

"I teach the Bible just the way it is," says Clark, "and the miracle just the way it says."

And that, say Bristol City Councilman Sam Crockett and his wife Sally, is why they have joined the Virginia chapter of the American Civil Liberties Union in asking a federal judge to halt the Bible classes.

Holding Bible classes on school property during school hours, the Crocketts maintain, violates the Constitution and 40 years of Supreme Court rulings by teaching one brand of religion--in this case fundamentalism--to a captive audience of impressionable children.

The lawsuit has provoked an unaccustomed furor in this predominantly Baptist city of 19,000 on the Tennessee border, splitting church congregations, pitting neighbors against each other and subjecting the Crocketts--pillars of the local establishment--to midnight phone calls and hate mail.

The Crocketts' lawsuit also has thrust this insular Appalachian city 400 miles southwest of Washington into the national spotlight. Officials of the Justice and Education departments say they are closely watching the Bristol case, which they regard as an important battle in the crusade, led by President Reagan, to resurrect religion in the nation's public schools.

Lawyers for the school board, however, say they are not teaching a particular religion but the Bible as a literary and historical classic, a practice the courts permit. They say they are offering fourth and fifth graders the chance for a "complete education" by sponsoring voluntary, non-denominational Bible classes paid for by a private church-funded group.

"The Bible is a very complex document if you're dealing with it on a theological level, but not as a storybook," said school board attorney G. Walter Bressler. "Our teachers make a careful effort not to draw moral, ethical and religious conclusions."

Others see a different meaning in the dispute over the classes, which have been part of the official school curriculum for the past 42 years.

"I think Bristol shows the very concerted effort, spearheaded by the ACLU, to completely secularize the schools," said Gary L. Bauer, a deputy undersecretary of Education who made a similar point in a recent letter to the newspaper here. "I think the president believes that's a very negative development that the founding fathers of this country never intended."

Bristol Sheriff Marshall Honaker, chief fundraiser for the Bible Defense Fund, which has raised $40,000 to defend the school board suit, agrees. "We just believe the Supreme Court was wrong in 1963 when it outlawed school prayer," said Honaker, a neighbor and Methodist Sunday school classmate of the Crocketts. "This is our way to get the decision changed."

The sheriff's views are echoed by others in this Bible Belt city where religious fervor and suspicion of outsiders run deep. Many of the more than 100 churches here and just across the Tennessee border display large signs asking, "Did You Think to Pray?" or reminding "You Have an Appointment with God." And many here are aghast at the Crocketts' alliance with the ACLU, which is about as popular here as the Politburo.

"Sam and Sally Crockett are puppets for the ACLU and going against the Bible is going to harm them for the rest of their lives," said Gene Kistner, a 32-year-old appliance dealer who presides over the private, church-supported group called Bible Teaching in the Public Schools, which sponsors the classes.

"I must believe they are clearly serving Satan and I pray for them," said Kistner. "In learning the Bible you're either for God or against God, and when the Bible says, 'Noah built an ark,' we believe Noah built an ark. Obviously they don't and have had incorrect Bible teaching."

Kistner and Honaker claim the overwhelming majority of residents here support the program, citing as evidence the fact that only a dozen of the 481 eligible students, among them 11-year-old Kathleen Crockett, don't take weekly Bible classes.

"In 42 years there have been almost no complaints," said elementary school principal Don Mumpower, 39, who took Bible classes when he was a boy. The classes are offered in the fourth and fifth grades, Mumpower said, "to implant the value of the Bible in children in their formative years . . . We've had some Jews, Catholics and kids without religion who don't question the content."

Some religious leaders say that while they oppose the classes as unconstitutional, it's often easier to let children attend.

"Of course we oppose it but there are so few of us here," said Leo Shankman, head of the 65-member B'nai Shalom Congregation. "We have very few Jewish children in the schools, and we haven't taken a public stand. I think the best thing is just to stay out of this."

The area's only Catholic priest also said he thinks the classes are unconstitutional.

"There is a lot of silent support for Sam and Sally but it's so dangerous to verbalize," said one Baptist minister who privately applauds the Crocketts' stand. "You have to realize Bristol is a small, ingrown community, and taking a public stand means you risk economic reprisals and total ostracism. It's sort of like being for integration in Mississippi in the 1960s."

Three years ago this area was the focus of a national controversy when a Baptist minister in adjacent Washington County tried to remove "Goodbye Columbus" and other books he branded "hardcore porn" from the public library.

The Bible suit has evoked similarly strong feelings. Billboards, some paid for by a local business, have sprung up here and on the Tennessee side proclaiming: "The Holy Bible: It Should Not Be Expelled!" Monthly fundraising rallies at area churches have attracted more than 700 people.

Recently the school board's insurance company announced its refusal to pay the legal costs of the suit, saying it would be a "fruitless act" because the classes "beyond question" violate First Amendment guarantees of separation of church and state. Since then, Bible class supporters have mounted a massive door-to-door fundraising campaign against the ACLU, distributing literature warning that the "very powerful and well-funded" group champions pornography, abortion, gambling and the overthrow of the U.S. government.

For months Bristol's two daily newspapers have carried letters to the editor and stories chronicling the controversy. After an editorial was published suggesting that the city should consider alternatives to the Bible classes, Kistner--who said his appliance business spent $25,000 on newspaper advertising last year--yanked his ads.

When an official at the Virginia Education Association in Richmond discussed the possibility of joining the ACLU suit, Kistner's aunt, Joyce Kistner, who heads the Bristol VEA chapter, threatened a mass withdrawal of her members. The VEA decided not to back the suit.

Sally Crockett, 46, a former local YWCA president who organized religious rallies as a college student, said she never dreamed her complaint to an elementary school principal would escalate into a national civil liberties case. "I was very naive then," she said, cracking a rueful smile. "This has been a real education."

Last year, Sally Crockett recalled, her daughter Kathleen, then a fourth grader, brought home a permission slip which must be signed by the parents of Bible class students. The Crocketts' elder daughter, Suzanne, now an 18-year-old college freshman, had taken Mildred Clark's Bible class and, according to Sally Crockett, was taught a literal interpretation of the Bible, hell and the devil that contradicted what she learned at home and in Sunday school.

"I didn't like the class when Suzanne took it but I felt she was better able to distinguish things for herself," said Sally Crockett. When the Crocketts refused to sign Kathleen's permission slip, which does not indicate the classes are voluntary, the girl was sent to the school library during Bible class. Her mother said she was told to read, be quiet and not look up for 40 minutes.

"Kathleen had thought reading was fun but instead she intepreted it as punishment," Sally Crockett said. When Kathleen returned to class she was approached by Clark, who sent home another permission slip and a note to the Crocketts.

"Kathleen is a very sensitive child who tries so hard to please and she came home crying, she was so upset," Sally Crockett recalled. The Crocketts decided to allow her to take Bible classes last year but told her she would not be permitted to take them in fifth grade.

In the meantime, they complained about the classes to the principal of Kathleen's school, the school board and the county school superintendent without success. They then turned to the ACLU, which failed to persuade school officials to move the classes off school property, as other Virginia jurisdictions have done.

Before filing suit Sam Crockett, 49, a lanky gray-haired man who chooses his words carefully, consulted his boss at Bristol Steel. His employer assured him the lawsuit would not affect his job as personnel director.

Crockett's job may be secure but his political career is not. Mayor Ronald R. Morgan has persuaded the City Council to pass three resolutions in favor of the Bible classes. Each time Crockett, a long-time Democratic party activist elected to the city council last year, cast the lone "no" vote. Morgan also has publicly called for Crockett's resignation and describes him as "politically dead."

"Well, I don't know about that," said Crockett, a former Capitol Hill aide, "but I never really had political ambitions anyway."

There have been other personal consequences: stares in the grocery store, snubs at church, abusive midnight phone calls and hate mail addressed to "You nitwits who should go back to Russia where you came from."

One child was pulled out of Sally Crockett's Girl Scout troop.

Last month Sally Crockett decided to stop substitute teaching after elementary school students left anonymous notes on her desk. One asked if she was "an atheist or something" and another pleaded with her to drop the suit "because my cousins don't go to church and Bible in school is there sic only chance to go to heaven."

"There has been a lot of quiet support, which really helps," said Sally Crockett, who one day returned home from a court hearing and found flowers sent by an anonymous supporter on her doorstep. The couple has been heartened by the public support of their minister, the Rev. Roger Hilton, pastor of State Street United Methodist Church. Last week, the bitterly divided church, which contributes $3,000 toward support of the classes, voted against letting Kistner's group hold a fundraiser before the June 27 trial before U.S. District Judge Glen B. Williams in nearby Abingdon.

The Crocketts say that Kathleen, who now spends Bible class time studying in a science class, has been upset by the experience. It helps, they say, that Hilton's daughter Alison and Kathleen's best friend, Katy Ford, are among the five sixth-graders who don't take the classes.

Last year, said Hilton, his 10-year-old daughter was forced to sit in the hall outside the principal's office during Bible class. "That's where they put children who are being punished. My daughter suffered, no question about it," said Hilton, who added that many members of his congregation wanted to know why a minister's daughter was skipping Bible class.

"They can say all they want that these classes are voluntary," said Gerald L. Gray, the Crockett's attorney, "but the message kids get is that good children take Bible classes and bad children don't. Religion is a very sensitive subject for children."

Sensitive or not, said Mayor Morgan, the Bible classes serve an exalted purpose. "We are the greatest Christian nation in the world and these classes are just supposed to build faith and spirit in children. If you take away a child's faith, or build no faith, you have less to live for," he said. "Hell, all these teachers are doing is trying to prevent these kids from becoming a bunch of raving radicals."