Claire Humphrey sounds like a typical suburban mom when she talks glowingly about her 7-month-old daughter, Lucy.

Then Humphrey, who is gay, starts outlining the challenges she and her partner, Vickie Henry, face caring for Lucy.

Those challenges, Humphrey said, would multiply if lawmakers and voters approve a change to the state Constitution defining marriage in Massachusetts as a union between one man and one woman. Massachusetts does not recognize gay marriage.

"I wouldn't be able to sign a permission slip for a school field trip let alone make medical decisions," Humphrey said.

Humphrey was among dozens of opponents of the ballot initiative who crowded a Statehouse hearing Wednesday.

Supporters of the question say they aren't targeting homosexuals, but just want to protect traditional marriage, which they say is under attack from gay activists and popular culture.

"There's nothing wrong with loving each other. There's something terribly wrong with destroying 4,000 years of a traditional relationship," said Chester Darling, a lawyer for Massachusetts Citizens for Marriage, the group pushing the initiative. "(Marriage) shouldn't be marginalized or trivialized by a bunch of people who hate it."

The initiative would also deny marriage benefits to other kinds of relationships, although supporters were unable to say what kind of benefits the question would ban.

"It may be a broad impact, but we don't know the specifics," said James Lafferty.

Opponents fear the question would block expanded legal rights to same-sex relationships and roll back benefits some gay couples and unmarried heterosexual couples now enjoy, including the right to adopt children, the chance to receive health benefits under their partner's insurance, and the ability to receive their partner's pension benefits after death.

Those details are important, said Humphrey, 43, who quit her job to care for Lucy. Humphrey receives health benefits through Vickie, 35, who works at a Boston law office. After Henry gave birth, Humphrey adopted Lucy to guarantee her rights as a parent.

Ballot question supporters' "concerns tend to be very general and very philosophic, while the concerns of the people who oppose the amendment are often extremely specific," she said.

"Two weeks ago when Vickie was 3,000 miles away and Lucy had a 103 fever, I had to be recognized as her mother," she said.

The question faces a long road to the ballot. Because it seeks to change the constitution, the question must win the backing of 25 percent of two back-to-back sessions of the Legislature. The earliest it could get on the ballot is 2004.

Most of those who attended the hearing opposed the measure, including state Sen. Cheryl Jacques, D-Needham, who is gay.

On Friday, Jacques' partner, Jennifer Chrisler, gave birth to twin boys. Jacques plans to adopt the children so she and Chrisler can act as parents.

"None of the marriages of the couples who live on the same block as Jennifer and I are threatened by our partnership," Jacques said. "Their marriages are not weaker because we too have chosen to build a life together."

The question is also under fire from backers of another initiative designed to block the sale of horses for human consumption.

Backers of that question have sued alleging workers for a signature-gathering company hired separately by supporters of both questions tricked voters into signing the marriage question by telling them they were signing the horse question.