An "America for Jesus" rally slated for Friday aims to attract 40,000 to 50,000 evangelical Christians to fast and pray for 18 hours on the Mall.
Although the rally is 11 days before the presidential election, organizers say the intent is spiritual, not political.
"It is not a political rally; it is a prayer and fasting rally," said Bishop John Gimenez, senior pastor of the 5,000-member Rock Church in Virginia Beach, who is leading the event. "We are going to pray and fast that God will bring healing to our nation.
"We're not going there with a fist raised in protest but with hands raised in worship. We know 'It's not by might nor by power but by the spirit of the Lord.' We feel the church needs to say to the nation, 'Our house is on fire.'"
The rally runs from 6 a.m. to midnight on the Mall at Seventh Street NW.
Bishop Gimenez's church staged similar large rallies on the Mall in 1980, 1988 and 1996 during times, he said, of national ferment.
"It seems that every eight years, God puts it on our heart to come back to Washington to pray," he said.
"We feel as ministers of the Gospel of Jesus Christ in this nation, we have a responsibility and obligation that whenever there's trouble nationally or internally that affects the whole nation, we have to come pray at our capital," Bishop Gimenez said.
The condition of the country is worse than it was in 1980, he added, when the major problems were soaring interest rates and U.S. hostages in Iran.
"A lot of things have happened now that are devastating to our nation," he said. "We feel America has become like the prodigal son. It's left its basic, righteous standing and gotten itself into the pigpen area with pornography and no prayer in schools. The church has the obligation to pray and to fast."
The numerous speakers include singer Pat Boone, Bishop Betty Peebles of the Jericho City of Praise Church in Landover, U.S. Senate candidate Alan Keyes of Illinois, National Association of Evangelicals President Ted Haggard, televangelist Rod Parsley, and Ben Kinchlow, a former co-host for "The 700 Club" on the Christian Broadcasting Network.
Bishop Gimenez said Friday's rally originally was for Hispanics only. When it became clear that Hispanic churches could not afford the $1.2 million cost, the bishop expanded it to other congregations.
"We haven't had too many people respond," he said. "It's been very difficult."
But Anna Gimenez, the pastor's sister who is in charge of organizing black and Hispanic churches for the rally, said "hundreds" of local congregations are taking part.
"I am getting the greatest response from Hispanics we've ever had in the city," Miss Gimenez said. "Usually we get the pastors, but not the people. But this time there's a move amongst them for a vision for America. They are no longer just visiting this country; America is their country, too."