When Charles Trentham left Knoxville, where he was pastor of one of the largest and most prestigious churches in town, to come to Washington and the First Baptist Church, there were some who thought he was accepting a demotion.

In Knoxville, the church had 3,600 members; he'd preach to 450 at an evening service, which is about as many as he gets on a Sunday morning here at 16th and O streets NW. The budget was twice that of First Baptist's, and he was a recognized leader of the community, a member of boards and commissions.

In his first 10 days here, the church was burgled six times. There has been a long-running dispute with neighborhood preservationists over the church's plans to expand, and services have been interrupted by antinuclear protestors and radical Christians setting off "laughing boxes."

All of this would be of little interest beyond the confines of the First Baptist congregation if not for the prominence of one member and his wife: the president of the United States and Mrs. Carter.

Since the Carters joined in January 1977, Trentham has achieved the "national platform" he sought in moving to Washington. But his sojourn here has also been marked with personal unhappiness after his second wife left him, and because of squabbles within the church that have surfaced publicly due to the visibility created by the president's membership.

Tomorrow the congregation is supposed to vote whether or not to renew Trentham's contract, after a negative recommendation from a majority of the board of deacons based largely on his unhappy marital record. While some sources say the attempt to remove Trentham is led by a small clique who don't like him or his relatively liberal politics, it is not known whether the friendship expressed by some prominent members is shared by a majority of the congregation.

"He is my pastor and my personal friend," said John White, chairman of the Democratic National Committee. "Obviously this is quite serious, but I certainly hope his contract is renewed."

Asked about the internal politics of the church, he laughed. "Baptist churches are always full of politics."

Trentham won't comment on the controversy; clearly if his contract is renewed he must look ahead to reconciling his detractors.

Trentham left Knoxville partly because things were getting too comfortable there -- "I was getting in a rut" -- and because he wanted to get away from the sad reminders of his first divorce.

So he came to the capital city and the national platform, bringing with him a fairly liberal theology and a kind of loping speech pattern he says comes from his mountain roots. He has a small-town touch that helps humanize the vaulted Gothic ceilings of First Baptist, and seems to be well-liked by the members of the congregation. He shares with them an unpretentious enthusiasm about having the president sit in their midst.

Trentham tells a story on himself about getting a call from the White House while he was playing volleyball at a church-sponsored youth camp in West Virginia.

"The kids came running to the court saying the White House was on the phone," he recalled "I turned in a hurry and sprained my ankle. I had to be carried to the telephone. I had an appointment to be at the White House at 6 p.m., but Rosalynn wanted to know if I could come over at 5. There was no time to go home and change after getting my ankle taped up, so I showed up at the White House on crutches and wearing my old trousers. I said to the guard at the gate, 'You're not going to believe this, but I'm Mrs. Carter's minister.' He looked at me and said, 'Oh, you must be from Plains!'"

Trotting over to the White House every now and then is not the only difference between pastoring here and in Knoxville. Here, members of the congregation live in the suburbs and commute downtown for church; the surrounding neighborhood has little relationship to the church. And "it takes three hours to make a hospital call with this traffic," Trentham lamented. With the smaller staff of First Baptist, he finds the demands on his time are such that he has little time to write.

Trentham, 60, was born in Jefferson City, Tenn., the son of a grocery store owner. He grew up in Knoxville, where he was later to preach, and knew he wanted to enter the ministry from the age of 12 after having a spiritual experience while walking home.

He sold his only two valuable possessions -- a watch and a Sam Browne belt from ROTC -- for $2.65 to pay for a train ticket to the church-sponsored junior college in Marshall, N.C., that he attended for two years.

The ticket cost $1.55, a detail he relates with precision.

In Washington, he lives in the posh Westchester Apartments and drives a Mercedes ("it's quite old") with the radio tuned to a classical music station. mHe's invited to official dinners at the White House.

He has a doctorate in theology from Southwestern Baptist Theological Seminary, where he was graduated with honors. He spent a year at the University of Edinburgh earning a degree in moral philosophy, and seven years as a professor in the systematic-theology department at Southwestern. In 1953 he moved back to Knoxville.

There he was popular and, for a Southern Baptist, a liberal. He organized a biracial preaching mission and belonged to a commission appointed by President Kennedy to look into racial troubles in Birmingham. He was identified with the civil rights movement in Knoxville.

During the worst of it, his two sons' lives were threatened, unidentified callers harassed his wife and members of a racist group tried to trap him into buying liquor from a bootlegger (there was prohibition in Knoxville at the time).

He supports the Equal Rights Amendment, has helped organize an antinuclear "Peacemakers" group (which started some of his current problems), was adamantly opposed to the Vietnam war and believes the church should be involved in social issues, a view that has historically divided Southern Baptists.

His sense of politics is not undeveloped. He is frank, for example, about his efforts to get the president and his family to sign on as members of First Baptist, rather than Calvary Baptist, which is the same distance from the White House.

"Well, face it, a man would be abnormal if he didn't want to be pastor to the president of the United States," Trentham said.

Trentham's professional success has not been matched in his personal life, a fact he frankly mourns. His first marriage ended after 31 years, his second after less than two. "I didn't leave these women, they left me," he said. "That says something about me I don't like."

Divorce is painful in any circumstance, but particularly so in the fishbowl world of a Southern Baptist preacher.

"I'm in a precarious position with my domestic tragedies," Trentham said. "There are those who feel I am not a good model for family life. I have no problem with that; there was a time when I felt the minister should be an unflawed model. Now I know that putting the minister on a pedestal is a grave disservice to the congregation. . . .

"I would like to have a home," he said sadly. His eyes glistened; he paused. "Although it's not the worst thing in the world for a minister to have the freedom to respond to calls at any hour of the day or night. I don't have to account for my time when I come home at 10:30 . . . I have two marvelous sons, I do have a family. And the church is so supportive and loving. It's an affection born of service, and I treasure it."