Membership loss and aging congregations are among causes of skyrocketing health care costs that have created major financial problems for the United Methodist Church and have led at least one regional conference finance chairman to predict that the problem could eventually "wipe out" the 9 million-member denomination.

The problem also has had a serious effect on the 14.9 million-member Southern Baptist Convention, the nation's largest Protestant denomination. And in one form or another, it has hit virtually all the major church bodies in the United States, reflecting the national crisis in health care costs.

The 72 annual conferences in the United Methodist Church have a variety of health plans, ranging from fully self-insured to wholly other-insured and a spectrum of coverage from minimal to comprehensive, according to Robert W. Stevens, treasurer of the Pacific Northwest Annual Conference.

Stevens also heads a 22-member committee created by the church's General Board of Pensions last September to study the possibility of a denomination-wide health care program.

According to the United Methodist Reporter, the problem in the denomination is caused by a combination of factors, including a steady membership loss, many congregations with fewer than 100 members, a "graying" membership that is mostly over 55 and an average conference income increase of no more than 5 percent each year.

The North Central New York Conference is a microcosm of the situation throughout the United Methodist Church.

When it was created through a merger in 1987, the conference had a 70 percent health care cost increase, amounting to $700,000. It covered part of the total by using $400,000 from a reserve fund set aside for ministerial pensions.

The Rev. William H. Stubbs, the conference's pension chairman, said the problem was compounded in 1988 when five medical claims exceeded $100,000 each, leading to a 30 percent cost increase in 1989. For 1991, the conference predicts another 30 percent rise.

The Rev. Harold W. Garman, conference finance chairman, said the regional body projects that the average local church share of health insurance will be $10,000 annually if costs continue to rise at the current rate.

"If this continues across the denomination at a similar rate, it will wipe out the United Methodist Church," Garman said.

To deal with the problem, the Central New York Conference's task force on medical insurance is proposing a plan under which cost payments will shift from the conference to local congregations.

Several months ago, the denomination's Southern New England Conference adopted a plan under which each local charge (one or more churches served by the same pastor) will be billed the same amount for health insurance -- $4,235 per pastor.

According to Stevens, who heads the national task force dealing with the health care cost problem, "Nobody's figured out a way to solve it -- not GM, not IBM, not the church. It's not a phenomenon of just the church; it's all across our society."

The Southern Baptist Annuity Board is switching insurance carriers to distribute more fairly the cost of providing health coverage.

In the last 3 1/2 years, the denomination's Church Medical Plan has suffered a drain on reserves as claims consistently exceeded premium dollars available.

The Southern Baptist plan, which has more than 23,000 participants, showed a $2 million loss in the first three months of 1990 despite an aggregate premium increase of 20 percent on Jan. 1, according to Harold D. Richardson, treasurer of the Annuity Board.

Individual rates went up from 5 percent to more than 40 percent, he said.

Last year, church and seminarian participants filed 256,552 claims totaling $64.2 million.

In characterizing the problem, John L. Dudley, director of the board's insurance services division, said that in 1989, the denomination paid almost $6 million in medical benefits for 32 people alone.

To help overcome such problems, the denomination is shifting insurance coverage from Aetna to Prudential as of July 1.

Although the change will mean an increase in premiums from 5 percent to 50 percent, the system will eventually become one based on a geographic rating "that assures lower rates where costs are lower and higher rates where costs are higher," Dudley said.