A February 2000 District Court ruling that sex is determined at birth and can never be changed was overturned in May, as an appellate panel outlined a formula for determining sex based on a mix of psychological and physiological factors. Since marriage is seen as a fundamental right, several legal experts said that if transsexuals like Mrs. Gardiner were barred from marrying men, they would probably be allowed to marry women. Indeed, after a Texas court invalidated a similar marriage in 1999, at least two male-to-female transsexuals have married women in that state.

''We're talking 'Brave New World' here,'' said Edward White, associate counsel of the Thomas More Center for Law and Justice, a public interest law firm that focuses on traditional values and is one of several national groups that have filed briefs on behalf of either side in the case. ''If a determination is made that a transsexual can marry, the next step would be homosexual marriage and lesbian marriage.''

But Jennifer Middleton of the Lambda Legal Defense and Education Fund, a gay rights group, says courts and legislatures lag behind science and society in seeing a blur between male and female. ''How much of what we think of as appropriate for a woman or a man is biologically determined versus socially constructed?'' she said. 'It's very difficult when the law tries to draw clear-cut lines saying that it's O.K. for a woman to do something but not a man, or vice versa.''

Mrs. Gardiner was born Jay Noel Ball with what she calls a birth defect -- a penis and testicles. As Jay Ball, she was married to a woman for five years, but at age 34 embarked on a transformation that included hormone therapy, a vocal-chord shave and cheek implants. After operations to create a vagina, Mr. Ball in 1994 changed his Wisconsin birth certificate to reflect a new name, J'Noel Ball, and sex, female.

In 1997, Ms. Ball, who has a Ph.D. in business from the University of Georgia, took a job at a college outside Kansas City, Mo., now called Park University. The following May, she met Marshall G. Gardiner, a former state legislator and chairman of the Kansas Democratic Party. They married four months later.