WASHINGTON - Experts and lawmakers differed sharply in testimony yesterday before the Senate Judiciary Committee over whether the institution of marriage is under judicial assault and can be preserved only through a constitutional amendment banning gay marriage.

In an opening statement, Sen. John Cornyn, a Texas Republican who is chairman of the subcommittee on constitutional law, decried what he said was a "judicial onslaught" against traditional marriage.

But Rep. Barney Frank, a Massachusetts Democrat who is openly gay, made the issue personal in emotional, unscripted testimony: "I have to ask, senators, who are we hurting? How is the fact that I or someone else wants to express love to another human being ... how does that hurt you? Why is this considered an infringement?"

Although congressional approval of a constitutional ban on gay marriage is considered unlikely this year, the hearings marked a new round in the intensifying struggle over the issue as the 2004 election campaign intensifies.

Cornyn dismissed as "myth" the notion that "my marriage doesn't affect your marriage" - a formulation he attributed to proponents of gay marriage to justify their position.

That, Cornyn said, "does not reflect reality. Redefining marriage in a way that reduces it to a financial and legal relationship will only accelerate the deterioration of family life."

The sponsors of the proposed amendment, Colorado Republican Sens. Wayne Allard and Rep. Marilyn Musgrave, testified that it was needed to prevent gay activists and judges from overturning state and federal laws defining marriage as a union between a man and a woman.

The charge that incorporating a ban on gay marriage into the constitution would enshrine discrimination in the fundamental document of American democracy "cheapens" the debate, Musgrave said.

Committee Democrats and some legal experts, however, argued that regulation of marriage is best left to the states.

"The issue of marriage," said Democratic Sen. Dianne Feinstein of California, "is the purview of the states, not of the federal government." Throughout U.S. history, she said, "the states have proved entirely capable of dealing with this issue."

University of Chicago law Professor Cass R. Sunstein testiiedd, "Those who endorse the amendment fear that if one state recognizes same-sex marriages, others will be compelled to do so as well." That fear, he said, "is unrealistic; the federal system permits states to refuse to recognize marriages that violate their own policies."

Democrats also took issue with Allard and Musgrave for rewording the proposed amendment on the eve of yesterday's hearing. The authors defended their changes as technical.

The new text reads: "Marriage in the United States shall consist only of the union of a man and a woman. Neither this Constitution, nor the constitution of any state, shall be construed to require that marriage or the legal incidents thereof be conferred upon any union other than the union of a man and a woman."

The sponsors deleted language that would have required that the amendment be ratified by three-quarters of the states within seven years. In the second sentence, they also deleted "nor state or federal law," which had followed the words, "Neither this Constitution, nor the constitution of any state."

The sponsors said the changes were meant to ensure that state legislatures could enact civil-union laws and grant benefits to domestic partners if they chose to do so.

Although Allard insisted that the amendment, as worded, would not "impact adversely any state's effort to deal with the issue of civil unions," he indicated he was open to further changes.

Whatever text is ultimately adopted by the committee, both Republicans and Democrats say the chances of Congress passing any marriage amendment in this election year are slim.

President Bush has publicly endorsed a constitutional amendment, although he has not specifically endorsed the Musgrave-Allard wording.

Times staff writer Richard Simon contributed to this article. The Los Angeles Times is a Tribune Publishing newspaper.