He added: "Increasingly, social conservatives expect real action, not just politically timed attempts to motivate and organize the base."
Other complain that Bush, despite Monday's planned event, has not put the full heft of the presidency behind the bid to ban gay marriage.
"President Bush's position is actually quite good on many ... life and family issues, but he needs to get out front on them," Tony Perkins, president of the Family Research Council, wrote in a message to supporters last week. There is also dismay among some activists over the wording of the amendment.
At least two prominent social conservative groups -- Concerned Women for America and the Traditional Values Coalition -- believe the language contains a loophole that would allow gays to seek civil unions.
The proposed amendment reads: "Marriage in the United States shall consist solely 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."
Andrea Lafferty, executive director of the Traditional Values Coalition, and others say the second sentence leaves open the option that gays and lesbians could enter unions other than marriage; and that's a deal breaker for them.
On its website, the Concerned Women for America says it "does not support the Marriage Protection Amendment as currently worded because the second sentence is open to differing interpretations."
Social conservative groups such as Focus on the Family, headed by James C. Dobson, support the amendment, despite the flaws they see in it.
"We would prefer stronger language, but we're content with this language," said Tom Minnery, Focus on the Family's vice president for public policy. "It leaves the issue of civil unions to the states. We recognize that this is the best we're going to get at the federal level."
White House officials sidestepped questions about the issue for most of this week. On Friday, White House spokesman Tony Snow said Bush had been an active opponent of gay marriage since he announced his support for the constitutional amendment in 2004.
And Snow dismissed criticism that the president had done little in the interim to make it a priority. "I don't know how you define what a priority is," Snow said. "The president has made it clear what he wants. He would like to see the Senate pass" the amendment.
