The event's main sponsor is the National Organization for Marriage, which engaged in several successful state campaigns against gay marriage prior to the 2012 votes in Maine, Maryland, Minnesota and Washington state that reversed the tide.
NOM is promoting the march with a website that evokes a "road to victory" and a video featuring dramatic background music.
"A competition is won by those who take the field, not by those who sit on the sidelines," NOM's president, Brian Brown, exhorts his supporters. "Friends, we need to take the field for marriage — and fight to win."
Brown, in a telephone interview, said his best-case scenario hinged on a future ruling by the Supreme Court upholding the right of states to set their own marriage laws, rather than imposing same-sex marriage nationwide. Such a ruling would strengthen the position of the 31 states that currently ban gay marriage and might encourage grass-roots efforts in some of the other states to reimpose bans, Brown said.
"We'd put this back in the hands of the democratic process," Brown said. "We would have the people deciding for themselves."
If the Supreme Court ruled the other way, legalizing gay marriage nationwide, "We won't go away," Brown said.
He envisioned a resistance campaign comparable to that waged by the anti-abortion movement since the Supreme Court's 1973 Roe v. Wade decision established a nationwide right to abortion.
"In the next year or so, we'll either have a massive victory at the Supreme Court, or we'll need to fight for 10, 20 years to undo the damage that the court has done," Brown said.
Among the scheduled speakers at the march is Austin Nimocks, senior counsel with Alliance Defending Freedom, a Christian legal group that has fought in court on behalf of laws banning gay marriage.
Nimocks argues that America would be better off if the Supreme Court allowed the current split among the states to continue, along with the public debate over the repercussions of gay marriage.
"America has not fallen apart because some states have same-sex marriage and others do not," he said. "We've been managing that for 10 years."
While Nimocks and Brown are optimistic that the Supreme Court won't impose same-sex marriage, other veterans of the fight against it think differently.
"Let's face it: Anybody who does not believe that gay marriage is going to be the law of the land just hasn't been observing what's going on," Sen. Orrin Hatch, a seven-term conservative Republican from Utah, told a radio interviewer last month.
Maggie Gallagher, a former president of the National Organization for Marriage, also expects that outcome. In a recent blog post, she said gay-marriage opponents needed to regroup and recognize that they have become "a subculture facing a dominant culture."
"The way you keep a movement going is to define achievable victories," she said in an interview. "The marriage movement is in the process of trying to figure out what that is."