When the congregation of the Mt. Horeb Baptist Church arrived at their church last Sunday, the air conditioning did not work and there were not enough pews. But what would have been a disaster for most other congregations on a hot mid-summer's day was a joyous occasion for the 500-plus members of the Mt. Horeb congregation.

After years of tolerating cramped conditions at their 108-year-old church at 216 16th St. NE, the congregation was about to participate in the dedication ceremony of their new church on Bladensburg Road NE. And even though the church was not completely finished, the service went on as scheduled.

"That's typical of our pastor though. He's a time-fiend," said one member of the congregation, commenting on the fact that the motorcade which brought members to the new church left precisely at 2:30 p.m. as arranged. "He's just that way. He had promised us that this church would be ready today and once that was set, that was it. He always said, 'I say what I mean and I mean what I say.'"

Words of praise for Mt. Horeb's 59-year-old pastor, the Rev. George Trueheart, were heard everywhere throughout the day.

"We never even gave a thought to moving until we got Rev. Trueheart," said one older woman, a member of the congregation for 35 years. "We just love him."

"It's beautiful. I've longed to see this day," said Sister Arizona Cousins, at 84 one of the oldest members of the congregation. "Rev. Trueheart can't be beat."

Since he became pastor at Mt. Horeb 27 years ago, the Rev. Trueheart, who was born and reared in the backwoods of King William County, Va., led the effort to acquire property adjacent to the old church that is worth $500,000 today, made possible by pledges and tithes. The sale of this property combined with the $400,000 expected from the sale of the old church and annex is being used to finance the construction of the new church. "We haven't taken a collection since 1956 and there hasn't been any fundraising," said Mrs. Trueheart with pride.

"That's what I like about this church," said Julia Smith, a self-described well-wisher and friend of the congregation. "They don't beg money. I always thought such a thing would be impossible without passing the plate."

One member, a Prince George's County school teacher, said, "You must understand that no more than 25 to 30 percent of the congregation, if that much, have any education beyond high school. Most are government workers and housewives. It's been quite a strain on the pastor to show them how they could tithe and still make it. Over 80 percent tithe, I believe, and even the senior citizens on fixed incomes contribute this way."

The new church, a red brick octogonal building that took only six months to build, seats close to 900 as compared with $350 in the old church, a quaint white brick building with blue trim built in 1870.

An architect and builder showed the pastor designs of other modern churches, explained Mrs. Trueheart, and the new church was based on a combination of these ideas. The idea settled upon - a round church - had to be modified somewhat for added room. "It was all mainly Rev. Trueheart's idea, though," she said.

"This is something we have really looked forward to," said the Rev. Julius B. Prince, an associate minister who came to Mt. Horeb six years ago.