ST. LOUIS — With their leaders saying that they stand at a historic crossroads, more than 900 Roman Catholic nuns have gathered here for a four-day meeting to decide how to respond to a biting Vatican assessment that cast them as disobedient dissenters and ordered three American bishops to overhaul the nuns’ organization, the Leadership Conference of Women Religious.


The nuns’ meeting on Wednesday in a vast hotel ballroom here exemplified the melding of traditional Catholicism and modern innovations that has so perturbed the Vatican. They sat in silence for a long stretch, sang songs about truth and mystery accompanied by a guitar and a choir, and heard a keynote address by a futurist who was escorted to the podium by seven liturgical dancers waving diaphanous scarves of pink and tangerine.


“Crisis precedes transformation,” the futurist, Barbara Marx Hubbard, told the nuns. “You are the best seedbed that I know for evolving the church and the world in the 21st century. Now, that may be a surprise to the world. But, you see, new things always happen from unexpected places.”


The nuns, most dressed informally in pants or skirts, gave a standing ovation to Ms. Hubbard, a beatific presence with a mantle of white hair who quoted Jesus, Buckminster Fuller, the Jesuit philosopher Pierre Teilhard de Chardin and the current pope, Benedict XVI.


But if the nuns submit to the Vatican’s plan to overhaul their organization, it is doubtful that their meetings will feature a keynote speaker like Ms. Hubbard, who grew up a nonreligious Jew in a Scarsdale, N.Y., mansion (her father founded the Marx toy company) and is now acclaimed by New Age luminaries like Deepak Chopra for helping to lead what she calls the “conscious evolution” movement.


The Vatican’s “doctrinal assessment,” issued in April, accused the nuns of a host of transgressions, including featuring speakers at conferences who did not adhere sufficiently to Catholic beliefs, advancing “radical feminist themes,” permitting “corporate dissent” on church teachings against birth control and homosexuality, and being silent in the church’s fight against abortion and same-sex marriage while pouring energy into working for the poor and disenfranchised.


The Leadership Conference, which represents about 80 percent of the 57,000 nuns in the United States, was formed in 1956 with the Vatican’s approval. (Other nuns belong to a more doctrinally conservative group, the Council of Major Superiors of Women Religious.)


The showdown between the Vatican and the nuns has provoked confusion and dismay among many American Catholics, who know nuns as teachers, nurses, social workers and parish administrators who have made sacrifices to serve the church.


When the nuns arrived for the conference on Tuesday night, their tables were strewed with letters addressed to the nuns from Catholics across the country. “Stand strong, speak your conscience,” said one from Madeline in California.


Another, from Christy, a middle school teacher in St. Louis, said: “You are the best that the Catholic Church has to offer. I pray you ignore any voices that speak otherwise.”


Sister Angela Milioto said that reading the letters made the nuns cry. She is a member of the Religious of the Sacred Heart of Mary, and she said of the nuns she was representing back home in Montebello, Calif., “They’ve spent their lives for the church, and they’re hurt.”


The conflict has also highlighted the rift between the church’s liberal and conservative wings, with some conservatives applauding the Vatican’s move to rein in the nuns. When Archbishop Robert J. Carlson of St. Louis announced that he would address the nuns here, his news release explained that he had played no role in planning the meeting or choosing its speakers.


In a brief but warm welcome on Tuesday night, he said he prayed that the “dialogue” between the Vatican and the nuns “is not politicized” but instead “worked out within the community of faith.”


The Vatican appointed Archbishop J. Peter Sartain of Seattle to oversee a rewriting of the group’s charter and teaching materials, to approve all speakers and conference programs, and to make sure that the nuns have the eucharist and proper liturgies at their conferences. A spokesman for Archbishop Sartain said he would not make a statement until he heard the outcome of the meeting, which is expected on Friday.


Many nuns said they were aware that the whole church was watching. Sister Pat Farrell, the conference’s president, told them, “This is an assembly like no other assembly we’ve ever had.”


But Sister Farrell hinted that the nuns might not be able to come to a clear conclusion. “The goal is not to come away from this assembly with a well-developed plan,” she said. “Our only hope is that as we touch into the collective wisdom that’s here that we can at least discern what is the next best step.”