If there are no last-minute legal hitches and Massachusetts on Monday becomes the first state to allow same-sex marriages, Lois Tetreault and Lois Johnson would like the pastor of the church they have attended for more than a decade to perform their wedding later this year.

But they have not asked the Rev. Cathy George of St. Anne's in-the-Fields here to officiate because they think she would have a hard time saying no. If she said yes, she could be hauled before an ecclesiastical court and lose her ordination as an Episcopal priest.

"Frankly, I find Cathy's ministry so important that I would not want to jeopardize it," Tetreault said.

Six months after its Supreme Judicial Court ruled that the state constitution guarantees the right to marry the partner of one's choice, Massachusetts is poised to put that historic decision into action by granting civil marriage licenses to gay couples. Legally, the ruling does not bind religious institutions in any way. Churches, synagogues, mosques and meetinghouses are free to hold gay weddings -- or not, as they see fit.

Yet the spillover across the church-state divide is huge. Many clergy and congregations are torn over what to do. Spurred by the state's action, some Massachusetts clergy of at least four major denominations -- Episcopalian, Methodist, Presbyterian and Conservative Judaism -- are openly weighing whether to disobey their denominational rules and risk disciplinary action by presiding over same-sex marriage ceremonies.

Just as the political shock waves of the Massachusetts court decision reverberated across the nation, many religious leaders think the theological ripples will spread outward.

At one end of the religious spectrum, the Unitarian Universalist Association, which espouses a set of ethical and spiritual principles but does not insist on belief in God, is staking its national reputation and future growth on wholeheartedly welcoming gay couples in Massachusetts.

Its president, the Rev. William G. Sinkford, plans to officiate on Monday at the wedding of Hillary and Julie Goodridge, the lead plaintiffs in the lawsuit that led to the court's decision. On Thursday, the Unitarian minister of Boston's 145-year-old Arlington Street Church will marry her lesbian partner, then perform marriage and civil license-signing ceremonies for other same-sex couples in 20-minute intervals all day long.

Not to be outdone, the United Church of Christ, which includes more than 400 Congregational churches in Massachusetts, will have volunteers dispensing cookies, coffee and congratulations when gay couples arrive at municipal offices to apply for marriage licenses.

"Our message is, 'You're welcome to get married in our church; we'd love to have you marry in our church,' " said the Rev. Fran Bogle, who is helping to coordinate the effort. "People are doing it as a really spontaneous outpouring of celebration, but I hope it will have the effect of gaining parishioners, too."

At the other extreme, the state's four Roman Catholic bishops have become more deeply engaged in opposing gay marriage than in any other recent political issue. In January, they sent mailings to a million Massachusetts households and made their first joint appearance in five years to lobby for a state constitutional amendment to override the court ruling. They were joined in that effort by evangelical Protestant activists from across the country who see Massachusetts as the front line in a culture war.

The theological ferment is mainly in the religious middle ground. Most of the clergy trying to draw fine lines and congregants struggling to decide where they stand are mainline Protestants and observant but not Orthodox Jews -- including some gay churchgoers themselves.

For Tetreault, 50, and Johnson, 57, the decision to obtain a civil marriage license was, in their words, "a no-brainer." Far more complex was the question of a church wedding.

Tetreault, especially, is an active worshipper at St. Anne's parish in Lincoln, a leafy, wealthy town 15 miles northwest of Boston. She could have her relationship blessed in a ceremony there, but it would not be the same liturgy as an Episcopal marriage service.

Or, Tetreault said, "I could easily find a renegade Episcopal priest to marry us" at another church. But she is not sure she wants that, either.

Raised Catholic, Tetreault said it took her a long time to find a religious community in which she felt truly at home. Now that she has it, she said, what she would like is a simple but soulful wedding in her own church.

But that's not possible.

"The fact is, we can't get married in the Episcopal Church. That might not always be true. But for now it is. So I have to decide where I fit in the whole realm of 'separate but equal,' " she said. "It could well be that as far as any kind of church ceremony goes, we might take a wait-and-see on that."

Parishioner James Ritchie, 65, said, "I'm all in favor of Lois having a wedding in the church. But I also understand there are people here who won't like it -- initially. In five years, it will be accepted."

The Episcopal bishop of Massachusetts, M. Thomas Shaw, instructed his priests on May 6 that they may conduct "holy union" ceremonies for gay couples but must not call them marriages or sign civil licenses.

The Massachusetts court decision has put Shaw, who is widely regarded as a liberal in the church, in a dicey position. He has publicly endorsed gay civil marriage. But if he does not enforce church laws that define marriage as a union of a man and a woman, other bishops could bring charges against him.

Tetreault's priest, George, said Massachusetts Episcopalians are mindful of the worldwide upheaval over the consecration of a gay bishop in New Hampshire last year. "The diocese of Massachusetts is trying to walk a very fine line between supporting the Supreme Judicial Court ruling and trying not to act in isolation from the larger Anglican Communion by going against the doctrines of the church," she said.

Nevertheless, the Rev. Carter Heyward, a feminist theologian at the Episcopal Divinity School in Cambridge, warned Shaw in a friendly letter last month that she plans to disobey his instructions. No stranger to controversy, Heyward was one of 11 women ordained in violation of church law in 1974, prodding the church into allowing female priests a year later.

"I would rather the charges be brought against me than against him, because I feel like I've been here before," Heyward said in an interview. "I understand why theologically this needs to happen, and I would be very glad to say it in a trial and have a whole community of colleagues and friends saying it, too."

The Rev. Martha Giltinan, associate rector of Christ Church in South Hamilton, said she doubts that Heyward or anybody else can make a convincing theological case for same-sex church weddings. In her view, the Bible and 2,000 years of Christian tradition define marriage as a heterosexual union and the diocese is engaged in "hairsplitting" and "gymnastics" that "belie the average person's understanding of what's going on."

If a gay couple is blessed by a priest in the church sanctuary before their friends and family, then signs a civil marriage license with a justice of the peace in the hallway, "what is that?" Giltinan said. "Of course, the couple and everyone present is going to describe it as a marriage ceremony."

The lines are no brighter in many other denominations.

The Reform and Reconstructionist movements of Judaism permit their rabbis to perform same-sex marriages, but not all will do so. Rabbi Ira L. Korinow, leader of a traditionally oriented Reform congregation in Haverhill, said he is willing to bless a gay couple and to call their union a "marriage" in English, but he would not use the Hebrew term for marriage, kiddushin. "I'm working within a system of Jewish tradition that I feel I have to respect," he said.

The Conservative and Orthodox branches of Judaism, on the other hand, do not permit same-sex blessings. But the senior rabbi of one of the largest Conservative synagogues in Massachusetts, the 1,200-family Temple Emanuel in Newton Centre, said that if a gay Jewish couple approached him, he would help them develop a commitment ceremony.

"I don't think it would be traditional Jewish marriage. Nor do I see this as a second-class citizen not quite as good as marriage," said Rabbi Andrew Warmflash. "I don't think it would be at a lower level of holiness."

According to rabbinical authorities, a reprimand would be the worst punishment a Conservative rabbi could receive for performing a same-sex ceremony. Many Protestant clergy, however, would be risking their pulpits. The question is how willing their peers and superiors are to enforce the rules.

After an openly lesbian pastor was acquitted by 13 ministers in an ecclesiastical trial outside of Seattle in March, the United Methodist Church tightened its policies against gay clergy and same-sex commitment ceremonies at a convention in Pittsburgh this month.

The Methodist bishop of New England, the Rev. Susan W. Hassinger, wore a rainbow-colored clerical stole and knelt in prayer with gay Methodists at the convention to show her opposition to votes condemning homosexuality. But she said last week she is obligated to enforce the rules.

"It's not my personal decision," she said. "It's following the Book of Discipline."

The Rev. William G. Sinkford is president of the Unitarian Universalist Association, which has welcomed gay couples.Julie Goodridge, right, talks with her daughter, Annie Goodridge, 8, as she irons Annie's dresses Saturday in Boston. Julie and partner Hillary Goodridge, center, the lead plaintiffs in the lawsuit that led to the legalization of same-sex marriages in Massachusetts, plan to wed Monday.