The change would lead to many intriguing questions: For example, would a man who becomes a woman be able to marry another man? (Probably.) Would an adoption agency be able to uncover the original sex of a proposed parent? (Not without a court order.) Would a woman who becomes a man be able to fight in combat, or play in the National Football League? (These areas have yet to be explored.)

The Board of Health, which weighs recommendations drafted by the Department of Health and Mental Hygiene, is scheduled to vote on the proposal in December, and officials say they expect it to be adopted.

At the final public hearing for the birth certificate proposal last week, a string of advocates and transsexuals suggested that common definitions of gender, especially its reliance on medical assessments, should be abandoned. They generally praised the city for revisiting its 25-year-old policy that lets people remove the sex designation from their birth certificate if they have had sexual reassignment surgery. Then they demanded more freedom to choose.

Michael Silverman, executive director of the Transgender Legal Defense and Education Fund, said transgender people should not have to rely on affidavits from a health care system that tends to be biased against them. He said that many transgender people cannot afford sex-change surgery or therapy, and often do not consider it necessary.

Another person who testified, Mariah Lopez, 21, said she wanted a new birth certificate to prevent confusion, and to keep teachers, police officers and other authority figures from embarrassing her in public or accusing her of identity theft.

A few weeks ago, at a welfare office in Queens, Ms. Lopez said she included a note with her application for public assistance asking that she be referred to as Ms. when her turn for an interview came up. It did not work. The woman handling her case repeatedly addressed her as Mister.

“The thing is, I don’t even remember what it’s like to be a boy,” Ms. Lopez said, adding that she received a diagnosis of transgender identity disorder at age 6. She asked to be identified as a woman for this article.