The judge in Vermont ruled that the women should "be treated no differently than a husband and wife." He established a visiting schedule and held the biological mother, Lisa Miller, in contempt of court when she failed to comply with it.

The judge in Virginia ruled that Ms. Miller had the sole right to decide who could see the child. He ruled that the former partner, Janet Miller-Jenkins, had no "parentage or visitation rights."

Legal experts say the decisions, which reached State Supreme Court here on Wednesday, are the first to present a direct conflict between two state courts on a substantial legal question arising from a same-sex couple's union. The decisions offer a preview, the experts added, of what are quite likely to be many similar conflicts around the nation.

Ms. Miller moved back to Virginia, where Isabella was born, in September 2003. The couple had visited Vermont briefly for the civil union ceremony in 2000 and lived there for more than a year after Isabella was born in 2002.

"When I left Janet," Ms. Miller said in a telephone interview, "I left the homosexual lifestyle and drew closer to God."

Ms. Miller-Jenkins, who declined to be interviewed, has said the couple planned and cared for Isabella together. She read a statement outside the courthouse after arguments on Wednesday.

"I sincerely believe," she said, "that it is best for my daughter that both of her parents continue to be an active, loving, responsible part of her life."

The justices here were largely skeptical of the arguments offered by a lawyer for Ms. Miller, who, like her former partner, had been known as Ms. Miller-Jenkins. The justices also indicated that they were working in uncharted territory.

"The assisted reproductive technologies are galloping ahead of existing law," Justice Marilyn S. Skoglund said.

A few minutes later, Justice Denise R. Johnson asked about the consequences of inconsistent rulings. A lawyer for Ms. Miller-Jenkins, Jennifer L. Levi, said the question was premature. A Virginia appeals court will hear arguments in that suit next Wednesday.

"I'm just trying to figure out what the effect of our decision is," Justice Johnson said, in a tone suggesting it might have no effect because Isabella and Ms. Miller live in Virginia.

The cases involve the interaction of two sets of laws. At the state level, Vermont and Virginia have laws that say the first court to take jurisdiction of a custody case should make the final determination. That would seem to help Ms. Miller-Jenkins here.

In November 2003, it was Ms. Miller, the Virginian, who filed papers in Vermont to dissolve the union. In them, Ms. Miller acknowledged that Isabella was a child of the union and asked the court to allow her former partner to have contact with the girl. Her lawyers have since taken varying positions. Ms. Miller now says she was confused and did not mean to acknowledge any parental relationship between her former partner and Isabella.

A 2004 Virginia law, the Marriage Affirmation Act, makes same-sex unions from other states "void in all respects in Virginia." Judge John R. Prosser, of Frederick County Circuit Court in Winchester, Va., relied on that law in October in granting sole custody of Isabella to Ms. Miller.

Two potentially conflicting federal laws add to the confusion. The Parental Kidnapping Prevention Act largely tracks the state custody laws and requires other states to defer to the first courts to hear such cases. But the federal Defense of Marriage Act says states need not give effect to same-sex unions.

Joan Hollinger, who teaches adoption law at the University of California, Berkeley, said the Vermont judge had the better legal arguments. But, Ms. Hollinger added, "Vermont courts are in practical terms powerless to enforce their valid orders in Virginia if Virginia courts simply say no."

If the states' highest courts issue conflicting decisions, the case could head for the United States Supreme Court, said Mathew D. Staver, a lawyer for Ms. Miller. Mr. Staver added that similar conflicts could arise from decisions in California, where State Supreme Court ruled last month that both people in a lesbian couple should be considered a child's parents in many circumstances. The Legislature in Sacramento passed a same-sex marriage law on Tuesday.

Ms. Levi disagreed, saying the case was an instance of the ordinary heartbreak after a family breaks up.

"It's an unfortunate reality that children get put in the middle," she said. "Ultimately, what this case is going to decide is whether children born to same-sex couples should be treated the same or differently as other children."

Andrew Koppelman, a law professor at Northwestern, addressed such case in a book on interstate recognition of gay marriages that Yale University Press will publish next year.

"If the Virginia court is correct," Professor Koppelman wrote, "then no parental right arising out of a same-sex marriage is secure anywhere in the United States."

Ms. Miller said Isabella neither knew about the case nor cares about its consequences. "She doesn't even ask about Janet," Ms. Miller said. "I am the only mother."

In Vermont, Judge Cohen held Ms. Miller in contempt in September for not allowing visits to Isabella. He has not imposed sanctions.

"The judicial system as a whole simply cannot allow parties to try to take advantage of legal and cultural differences," he wrote, "which may make one state favor the position of a particular party over another."

Ms. Miller said she found the idea that a court could force her to allow Isabella to visit Ms. Miller-Jenkins particularly hurtful. "It would be like somebody off the streets coming and taking my daughter," she said. "They have no ties to my daughter."