The Rev. Gregory Trueheart was preaching a sermon that morning on the "Lawless Tongue." The minister told the congregation at Mount Horeb Baptist Church in Northeast Washington about a man who came to him, lawless tongue a-waggin', and said he could go down to that District Building and clean up the whole mess, fast.

"Yes sir, uh-huh," the reverend said he told his friend. "You'd get yourself on down in there and you'd make a fool of yourself, yes sir, and you'd make a fool of me. . . . No, no."

"What we need down there," the reverend went on, "is someone who knows how to do the job, yes sir!"

Betty Ann Kane, a guest at the church that day, blushed with pleasure. It was the perfect kind of verbal backdrop for her campaign to be mayor of Washington, a town where upstanding churchgoers are considered an especially potent political force.

Trueheart's words had touched Kane's campaign theme, which is that the city needs a leader who can make what she considers a bungling bureaucracy work, who can make the water bills right, who can make the budget numbers add up and who can get jobs in this city for the unemployed who are driving up the crime rate.

Kane, 40, has been preaching that line in Anacostia and Capitol Hill, in front of truckers and gay rights groups and a host of others almost nightly for the last month in her campaign for mayor, which to scheduled to be officially launched today.

Her candidacy to defeat Mayor Marion Barry and others in the Sept. 14 Democratic primary is an all-or-nothing fight because her current term as an at-large City Council member expires at the same time as Barry's first term as mayor. If Kane does not replace Barry she could be out of District government for the first time in seven years.

To stay alive in District politics Kane is counting on a constituency that has carried her to four victories and no losses in citywide elections, enabling her to win election to the Board of Education and the City Council. She describes her backers as public school parents, left over from her days on the school board when she helped to oust the controversial superintendent Barbara Sizemore, and the homeowners, middle-class taxpayers and small businessmen who have applauded her stands against tax increases and new taxes--particularly last year's increase in estate taxes, which passed the council with only Kane voting in opposition and later was overturned by the council as a wave of public criticism washed over them.

As for why she wants to be the mayor, Kane is clear in telling every group she talks to that she is "sick and tired" of being a council member and "passing laws and budgets that, no matter how good, are ruined because they are stalled or not carried out by the executive."

"Those of us who work there every day see it as a never-never land," Kane told the D.C. Builders Association about life in the District Building. "Some city officials appear to be anxious to solve the world's problems while the city's problems fester and smolder. Others think that emergency legislation--passed without notice and without deliberation--is the key to good government. Your city government takes in and spends so much money and treats it with such a cavalier attitude that I've concluded that our government must think it's not the taxpayer's hard-earned money it's spending, but Parker Brothers play Monopoly money.

"I'm running for mayor because that has to change."

Kane regularly gets applause for lines like that. But so far she has not attracted the money necessary to mount a major campaign.

Despite showings in various polls that a tall, thin, white woman from Tenafly, N.J., is a surprisingly popular politician in a 70 percent black city, when the first campaign finance reports were filed at the end of last month--reports some considered the first indication of candidate potential--Kane finished last among the major contenders. She collected only $24,860 of the unprecedented amount--nearly half a million dollars--contributed thus far.

Kane had been expected to draw considerable financial support from the real estate industry because she has come the closest of any city politician to opposing rent control in any form, and was the council member who opposed the council's repeated use of 90-day emergency legislation to stop condominium conversion.

"Betty Ann's not off to the fastest start," says G.V. (Mike) Brenneman, president of the Washington Board of Realtors, who emphasized that his support of Kane so far is only personal. The board has yet to back any candidate. "I think people aren't really convinced she's really in the race. She's just got to reiterate it and make personal appearances."

Dan O'Leary, president of the Builders Association, said, "I'm not sure people believe she can win. Once they become convinced she has a chance, they'll give her anything."

Ray Howar, a developer who helped to raise money for former City Council chairman Sterling Tucker in the 1978 Democratic primary for mayor but who plans to help Kane raise money this year, said, "It's a little too early to say she is not doing well. I don't think she has really gone after the money yet."

Part of Kane's political dilemma, observers say, is the fact that she is white and running for the top elective office in a mostly black city. Black politicians are very jealous of the prominence they have gained since 1974, when the District first elected its own mayor and City Council. Kane is having to convince campaign donors that while she may rankle some city black politicians, she is not threatening to the city's black voters but rather is popular and can win.

Kane's own polls have indicated, she says, that voters believe the mayor of the city need not be black to be effective. Kane is now pointing out in many of her speeches that her campaign has grass-roots support among "every group in every part of the city."

"I have always been a minority politician in this town," Kane says about the race issue in her campaign. "And I've always dealt with it by simply appealing to the people directly. I've always found race to be a more a question in the minds of the politicians and the press than with voters. They don't want to be judged on the basis of their skin color and I've never seen any evidence that they judge a politician's effectiveness on skin color."

Kane came to Washington in 1967 after getting her master's degree in English from Yale University. She worked as an assistant professor at Catholic University before becoming the development officer of the Museum of African Art and later director of public programs at the Folger Shakespeare Library.

A tall woman with a starchy smile that she flashes constantly in public, Kane is married to a lawyer, Noel, and they live on Capitol Hill in a town house with their two children, both of whom attend District public schools. Her daughter attends the new academic high school.

Kane's political career began when Barry resigned from the school board to move to the City Council. She won an election for the remainder of his term and then won a full term on the board in 1975. In 1978 she ran for her current council seat, beating H.R. Crawford, now the council member from Ward 7, in the Democratic primary for the at-large seat and easily winning the general election. Kane's interest in running for mayor after one term on the council and one term on the school board has prompted criticism of her as being overly ambitious and opportunistic.

"I don't think she's ready for mayor," says R. Robert Linowes, a supporter of Barry's who has already given the incumbent a $1,000 campaign donation. "She does her homework, but what good is it if she can't work with other polticians to get the right thing done? She was a member of the council that approved the estate tax even if she voted against it . . . she doesn't have the power base for the mayor's race either."

"She gives me the impression," Linowes added, "of not being sure if she is liberal or conservative. To vote for her, people want to have an understanding of a candidate's reasons and philosophy. Other than wanting to be mayor, she is hard to read."

Kane objects to being called overly ambitious. "Maybe when women do it, it is ambitious," she laughs. "When men do it they are called hard-working and successful. I made the decision to run for mayor only in the last six months and I did it because I care that the job gets done right."

Kane's campaign organization draws from groups she has dealt with during her political career, particularly from people she met while on the school board: Her campaign cochairpersons include Marilyn Tyler Brown, a supporter of Sterling Tucker in the '78 mayoral race who works for the school system; Bob Boyd, the former director of D.C. Citizens for Better Public Education; John S. Woodson, the husband of former school board president Minnie S. Woodson; and John R. Risher Jr., former corporation counsel in the Walter Washington administration. Kane's campaign manager is Dianna Brochendorff, who worked for Marion Barry in 1978.

On the campaign trail, Kane usually chooses to tout her independence and to rail against what she considers an inefficient and insensitive city bureaucracy. She sometimes runs into skeptics, like one lady at a recent meet-the-candidate gathering at a renovated row house on Swann Street NW.

"Some of us liberals," said the young, blond woman in a down-filled vest, "thought things would get better with Marion. I voted for him. Things got worse. A lot of people like me wonder can anybody do that job or is the whole city government filled with inept bureaucrats. I don't know if the level of competence and enthusiasm can make any difference."

Having already told the half-dozen people in the living room that 60 percent of the people interviewed in her poll said they wanted a new mayor, Kane was quick to reply.

"I don't like to make promises," she said, "but when I'm mayor, I plan to send a message all the way down to the bottom of the bureuracy. The people in the D.C. government can do the job, with a couple of reservations, but they haven't had the leadership. The major failure of Barry is not having reached into that mid-level and bottom level of government to build morale."

At the start of the Sunday afternoon meeting on Swann Street, the hostess, Carol Mindell, told Kane that many of the people she had asked to come told her they liked Kane but wished she was still running for council.

"Tell them," Kane told the group, "that people said the same thing when I was leaving the school board to run for the council. I remember in '78 Marion Barry called me into his office and told me I was a woman, I was white and I couldn't win a seat on the council. I won by a larger percentage against four opponents than Marion Barry did against three opponents."

Barry was unavailable to comment on Kane's recollection of their meeting, which Kane has shared with other groups as well.