A former Christian Science practitioner and a congregation here are challenging policies of the Board of Directors of the Mother Church in Boston.

Steven Evans said that if the board refuse to change conformity from the tinues to demand conformity from the First Church of Christ, Scientist, here, the dissenters would form a new Christian Science body.

The dispute is based on a letter circulated to local Christian Science leaders and practitioners in late 1975 by Reginald Kerry, who had been a Christian Scientist for 40 years. In the letter, Kerry charged "gross mismanagement, inexperience and lack of Christian ethics" at Mother Church headquarters.

Officials at the Boston headquarters said that Kerry's charges were unfounded and cited information in a rebuttal of the accusations. But they refused to divulge membership figures.

Last fall, Evans and other Christian Scientists organized a group called United Christian Scientists to press for more information from the board of directors. They asked, among other things, why the construction costs of the new Church Center in Boston had risen from an original estimate of $8 million to a final total of $92 million, and why members of the board were paid "upwards of $60,000."

Although officials of the Mother Church released some information, Evans and the other dissidents were not satisfied. They pressed for further details, and Evans was dropped from membership. The board of directors then warned the congregation in Plainfield that it could also be expelled if it continued to support Evans and the United Christian Scientists.

At a recent meeting of 68 of the 120 members of the Plainfield congregation, those present voted unanimously to send a letter to the board of directors, expressing their continued dissatisfaction.

An official at headquarters of the Mother Church said the cost overrun was due largely to strikes, materials delays and inflation. He said the $8 million figure related to "early speculations," and that the contractor's cost figure given to the Church in 1967 was actually $35 million. According to the official, the final cost was $82 million, not $92 million.

According to the same spokesman, the figure of upwards of $60,000 a year for directors' salaries "includes a court-regulated fee for service as trustees under the will of Mary Baker Eddy."

He pointed out that "the scope of the assignment for today's board is far greater than it was for their predecessors in the earlier days of a church that was founded by Mrs. Eddy and only 26 followers."

Evans indicated that he was not satisfied with these explanations and that he and the other dissidents want to examine the books of the Mother Church.