A little-known bishop in Lincoln, Neb., has sent shock waves through the Roman Catholic Church by threatening to excommunicate Catholics in his diocese by May 15 if they do not resign from a dozen groups he deems "totally incompatible with the Catholic Faith."

The forbidden groups include several challenging church teaching on abortion, birth control or the ban on female priests. But one group -- Call to Action, a Chicago-based group promoting church reform -- counts among its members thousands of priests and nuns and several American bishops.

The decree issued a week ago by Bishop Fabian W. Bruskewitz is extraordinary for a church in which many members routinely question church doctrine yet are counted nonetheless as faithful believers. Catholic scholars cannot recall any other American bishop in recent history issuing a blanket call for automatic excommunication.

"The other bishops are utterly distressed over this," said the Rev. Richard P. McBrien, a theologian at the University of Notre Dame and author of the Encyclopedia of Catholicism. "They're rolling their eyes and shaking their heads. And if they haven't already got to him, they will get to him soon and tell him to back off. He can't enforce this."

Other groups on the bishop's list include: Planned Parenthood and Catholics for a Free Choice, which support abortion rights; the Hemlock Society, a national right-to-die group currently promoting euthanasia legislation in Nebraska; the Freemasons and their affiliates DeMolay, Eastern Star, Job's Daughters and Rainbow Girls, all Masonic organizations long forbidden under church law; and St. Michael the Archangel Chapel, the local affiliate of a breakaway church founded by French bishop Marcel Lefebvre, who was excommunicated in 1988.

The bishop issued his warning a few days after receiving a letter from the co-chairs of the newly formed Nebraska chapter of Call to Action requesting a "dialogue" with him. Call to Action is a Chicago-based group with about 15,000 members that advocates such reforms as ordaining women and married Catholic men. Pope John Paul II has said that the ban on women's ordination stands and will not be reconsidered.

In a brief but acerbic response to the co-chairs of Call to Action Nebraska, Bruskewitz wrote that "the difference between a dissenting Catholic and a Protestant is that the Protestant has integrity. . . . Your organization is intrinsically incoherent and fundamentally divisive. It is inimical to the Catholic Faith, subversive of Church order, destructive of the Catholic Church discipline, contradictory to the teaching of the Second Vatican Council, and an impediment to evangelization."

He signed the letter "Sincerely yours in Christ Jesus."

Bruskewitz's warning about excommunication was printed last week in a small box on page three of the diocesan newspaper under the heading "Extra Synodal Legislation." It applies only to Catholics in his diocese. The bishop felt the move necessary because parishioners had made inquiries to the diocese about these groups, and participation in any of them could "endanger the salvation of one's soul," said Monsignor Timothy Thorburn, chancellor of the Lincoln diocese.

The warning "is medicinal, to call the person back to the faith," Thorburn said. "It's not like the shunning that is done in other religions."

Excommunicated Catholics are not expelled from the church, but are forbidden from receiving the sacraments, such as the Eucharist, being married in the church or being anointed when sick.

"This is the ultimate of the penalties and one which is used nowadays very, very rarely," said Monsignor Frederick R. McManus, professor emeritus of canon law at the Catholic University of America and editor in chief of the Jurist, a journal on church law. "It is exceptional because while the general {church} law allows a bishop to do this, it does express pretty strongly that he shouldn't do it except in serious situations."

Thorburn said that it will be up to each Catholic in the Lincoln diocese to refrain from taking the sacraments if they belong to any of the banned groups. "If a person was recalcitrant and they defied the sanction and received Holy Communion anyway, it would only prove the fact that they had no respect for the authority of the Catholic Church anyway," he said.

Randy Moody, a Catholic who sits on the boards of both Planned Parenthood Lincoln and the national Planned Parenthood Federation of America, said he would simply defy the ban. "I'm not going to quit Planned Parenthood, and I'm not going to excommunicate myself," Moody said. "My conscience tells me that I can belong to both organizations."

Lori Darby, co-chair of Call to Action Nebraska, regularly attends Mass, attended Catholic schools for 12 years and was once a member of a religious order. For her the excommunication order is very painful, she said, "a wrenching away from what you believe was a love relationship, with Jesus Christ, with your faith."

Call to Action is considering appealing Bruskewitz's order. They could appeal to the local archbishop or directly to the Holy See, experts in church law say.

Bob Heineman, a spokesman for Call to Action in Chicago, said, "There is a real sadness that this is the reaction this particular bishop has chosen because the Catholic Church has always included a very broad spectrum of belief."

"If the bishop thinks he's going to keep things quiet, he's wrong," Heineman said. "Our phone has been ringing off the hook with people saying, I want to join.' "

Several bishops who are members of Call to Action or who have spoken at the group's conferences refrained from commenting on Bruskewitz's action out of respect for a fellow bishop's authority over his own diocese.

Bruskewitz, who served in the Vatican's Congregation for Catholic Education for 10 years, was consecrated bishop of Lincoln in 1992. His diocese, one of three in Nebraska, includes 85,000 members. He is one of only two American bishops to forbid girls to serve at the altar. The other is Bishop John R. Keating of Arlington.

As word of the Nebraska controversy spread this week, groups of Catholics at both ends of the spectrum sounded off. The conservative Catholic League for Religious and Civil Rights praised Bruskewitz, saying, "There is a stark difference between those Catholics who privately struggle with certain Church teachings and those who organize to sow the seeds of discontent."

On the other hand, said Denise Shannon of Catholics for a Free Choice, "If you excommunicated all the Catholics who disagreed with non-infallible church teaching you'd have a very small church indeed." CAPTION: Bishop Fabian W. Bruskewitz leaves St. Patrick's Church in Lincoln, Neb., Wednesday. Bruskewitz's decree has evoked sharp reactions throughout the church.