NEW YORK -- Members of the Republican Party's platform committee yesterday strengthened the party's official opposition to same-sex marriages, a day after Vice President Dick Cheney broke with the Bush administration by saying the matter of gay marriage should be left to the states to decide.
The draft platform already included a call for a constitutional amendment to ban gay marriage nationwide, an element that was not in previous party platforms. And the section on social issues was amended yesterday to go further, with language added stating that the benefits of marriage ''should be preserved for that unique and special union of one man and one woman," a statement that appears to reject Vermont-style civil unions in addition to gay marriage.
''We believe and the social science confirms that the well-being of children is best accomplished in the environment of the home, nurtured by their mother and father, anchored by the bonds of marriage," the draft platform reads.
The plank was approved last night without discussion or deliberation by the 110-member platform committee, which was meeting at the Jacob K. Javits Convention Center in New York. The committee also approved language that affirms the GOP's support for a constitutional amendment to ban abortion.
Earlier in the day, the additional language on marriage and abortion was endorsed by a panel of delegates who were charged with crafting the platform's statements on family issues. The panel's 16 members had previously rejected efforts by gay-rights and abortion-rights groups to temper the language with more neutral statements.
The entire platform is to be voted on by the delegates at next week's Republican National Convention.
The platform's positions on gay marriage and abortion rights reflect the Bush administration's close association with the positions of the party's conservative wing, and appear to run counter to the party's efforts to convey a more centrist image, especially during next week's convention.
Gay-rights groups denounced the platform as discriminatory, and seized on Cheney's Tuesday comments to make their point.
''There are millions of Republican families who don't want to see their sons and daughters written out of the Constitution," said Cheryl A. Jacques, president of the Human Rights Campaign and a former Democratic state senator from Needham. ''It must be very hard for these families, including the vice president's, to reconcile their own support for inclusion with this divisive platform."
On Tuesday, Cheney made a rare public reference to his daughter's sexual orientation and stated his general support for gay rights. He also strayed from President Bush's stated policy by saying he believes the issue of gay marriage should be handled by individual states, reiterating a statement he made as a candidate for vice president four years ago.
''Lynne and I have a gay daughter, so that's an issue our family is very familiar with," Cheney said Tuesday in Davenport, Iowa, in response to a question from an audience member. ''Historically, that's been a relationship that has been handled by the states. The states have made that basic fundamental decision in terms of defining what constitutes a marriage."
Cheney went on to say that the ''president makes policy for the administration," and that the official Bush administration policy remains support for a constitutional amendment that would define marriage as between one man and one woman. Such an amendment would strip states of the right to grant marriage benefits to same-sex couples.
Yesterday, Cheney made a daylong campaign bus tour through eastern Pennsylvania, stopping at two rallies and a town hall meeting. Mary Cheney, the Cheneys' gay daughter, traveled with her father but remained offstage.
The vice president was instead introduced by his wife, Lynne Cheney, and his other daughter, Liz Cheney Perry, who was accompanied by her three daughters.
''My other daughter, Mary, is somewhere around here," Lynne Cheney told a cheering crowd of about 2,200 gathered at a high school gym in Pottsville, Pa. ''I believe she's working."
The Cheneys made no reference to the gay marriage issue during yesterday's campaign stops. The vice president revved up the crowd in Pottsville with his argument that in the war on terror ''a good defense is not enough, so we've gone on the offense."
Cheney's Tuesday comments continued to provide fodder for speculation and debate among Republicans on both sides of the gay marriage issue. Moderate voices within the party were hoping the comments would help them change the platform's language on the issues of gay marriage and abortion rights in particular.
Patrick C. Guerriero, executive director of the Log Cabin Republicans, the largest group of gay Republicans, said the party's platform is ''insulting" to swing voters and Republicans who support gay rights. Guerriero, formerly mayor of Melrose and briefly a candidate for lieutenant governor, added that it is also politically unwise to alienate the moderate voters whom the party needs to attract.
''If the Republican Party focuses on divisive cultural war issues, it divides our party, it divides the country, and even divides the White House," Guerriero said yesterday on CNN's ''Inside Politics." ''That's bad for George Bush, and that's bad for the future of the Republican Party."
But Gary Bauer, who ran for the GOP presidential nomination in 2000 and now heads a conservative think tank, said Cheney's comments could weaken the administration's support from social conservatives. He said yesterday's vote on the platform reaffirms Republicans' strong sentiments in favor of preserving the traditional definition of marriage.
''From a policy standpoint, [Cheney's] comments are irrelevant," Bauer said. ''From a political standpoint, it's harder to figure out the impact. But at the very least, it runs the risk of demoralizing voters that the president needs very much if he's going to have another four years."
In May, Massachusetts became the first state in the nation to allow gay couples to marry. The Legislature has voted to ban gay marriage and establish civil unions instead, but that measure cannot become law until voters approve it, and they will not have that chance until at least 2006.
Bush's Democratic opponent, Senator John F. Kerry of Massachusetts, opposes gay marriage but believes the matter should be considered by the states. A GOP-led effort to pass a federal constitutional amendment to ban gay marriage failed in the Senate last month.
Nina J. Easton of the Globe staff contributed to this report from Pottsville, Pa. Klein reported from Washington, Mooney from New York.