Gearing up for a July 12 Senate vote on a proposed constitutional amendment against same-sex marriage, evangelical Christian leaders yesterday urged churches across the country to declare July 11 "Protect Marriage Sunday."

In an e-mail to supporters, the Rev. Jerry Falwell predicted that "thousands" of churches would participate. He called on all pastors to "lift up the God-ordained institution of marriage in their sermons" and to hand out cards listing Senate phone numbers, "making it very easy for people to call their senators the next day."

James Dobson's Focus on the Family, Gary Bauer's Campaign for Working Families and the Rev. Donald E. Wildmon's American Family Association are also promoting the event. In its "Pastor's Weekly Briefing" yesterday, Focus on the Family listed some of the problems "that may arise" if the Constitution is not amended to ban same-sex marriages:

"The words 'husband' and 'wife' will be meaningless. . . . Our kids will be taught how to perform 'safe sodomy' in their sex education classes. . . . Churches will be pressured to either abandon the Scriptures or lose their tax exempt status if they refuse to 'marry' homosexuals," it said.

Gay rights advocates accused evangelical leaders of resorting to scare tactics.

"No religious organization will be forced to marry same-sex couples" if the Constitution remains unchanged, said Cheryl Jacques, president of the Human Rights Campaign. "It's very telling that they have to lie in order to attempt to stir the passion of their followers."

Since Massachusetts became the first state to issue marriage licenses to gay couples on May 17, conservative leaders have been lamenting the passivity of their grass-roots supporters. Falwell's e-mail quoted Paul Weyrich, chairman of the Free Congress Foundation, as saying that "too few calls, too few letters and too few faxes are coming into" Senate offices "in defense of marriage between a man and a woman."

Growing numbers of religious leaders, however, are weighing in on both sides of the issue. Bishop Wilton D. Gregory of Belleville, Ill., president of the U.S. Conference of Catholic Bishops, yesterday endorsed the constitutional amendment and urged all Roman Catholics to lobby for its passage.

Twenty-six religious groups, meanwhile, have sent a letter to Congress opposing the amendment. "It is not the task of our government and elected representatives to enshrine in our laws the religious point of view of any one faith," said the June 2 letter, whose signers included leaders of the Central Conference of American Rabbis, the Episcopal Church USA, the Evangelical Lutheran Church in America, the Presbyterian Church (USA), and the Sikh Council on Religion and Education.