A Democratic presidential candidate, John Edwards, turned up the heat on Senator Clinton and his other potential 2008 challengers yesterday, saying that it is “no longer okay to study your options” when it comes to the Iraq war.

Speaking at Manhattan’s Riverside Church, Mr. Edwards evoked Rev. Martin Luther King Jr.’s denunciation of the Vietnam War, which was delivered at the same church, behind the same pulpit. King’s son Martin Luther King III sat in the audience on the eve of the national holiday that honors his father. Mr. King introduced Mr. Edwards and praised his commitment to fighting poverty.

“If you’re in Congress and you know this war is going in the wrong direction and you know that we should not escalate this war in Iraq, it is no longer okay to study your options and keep your own private counsel,” said Mr. Edwards, who advocates withdrawing 40,000 to 50,000 American troops from Iraq. “Silence is betrayal,” the former senator from North Carolina said, echoing King’s words in his “Beyond Vietnam” speech. “Speak out and stop this escalation now. You have the power, members of Congress, to prohibit this president from spending any money to escalate this war — use that power.”

Mr. Edwards — whose call to block Mr. Bush’s proposed escalation was greeted with a standing ovation from the more than 1,000 people packed into the sanctuary at the church — said he was wrong for his 2002 vote to authorize the war.

The Democratic Party’s 2004 vice presidential nominee said there will “never be a military victory in Iraq” and that it was time for America to restore its “moral leadership in the world.”

His speech, delivered in Mrs. Clinton’s political backyard, seemed designed to both send a message to sitting members of Congress and to set up a clear contrast between his candidacy and the Democrats and Republicans preparing to enter the 2008 race. It came on a weekend when debate about the president’s new strategy for Iraq occupied much of the airwaves and newsprint.

It also came as Mrs. Clinton and other members of the Armed Service Committees in Congress took part in the final leg of a trip to Iraq, Afghanistan, and Pakistan, where they met with military leaders, American troops, and Middle East leaders.

In a television interview over the weekend, Mrs. Clinton expressed doubts about the war, suggesting that she may strengthen her opposition when she returns to Washington tomorrow. According to public reports, she told ABC News, that the violence in Iraq was “heartbreaking” and that “I don’t know that the American people or the Congress at this point believe the mission can work.”

Yesterday she met with President Karzai and President Musharraf.

Mr. Edwards has the luxury of speaking his mind without having to cast a vote, while those Democrats still in office have a more delicate task.

Senator Obama, who has been critical of the war, had not yet been elected to the Senate in 2002 when Congress voted on authorizing the war. Senators Biden of Delaware and Dodd of Connecticut, both Democratic candidates for president, voted in favor of authorization, but have since come out against the war.

“We need to look at what options we have available to constrain the president,” Mr. Obama said yesterday, according to the Associated Press.

Meanwhile, Mr. Bush and Vice President Cheney vowed yesterday to forge ahead with their plans to send 21,500 more American troops. The issue is expected to come to a head this week when the two chambers of Congress vote on non-binding resolutions on the war. More than anything those resolutions will force a number of the potential 2008 Democratic presidential candidates to clearly stake out their positions on how to proceed in Iraq.

Mr. Edwards was introduced yesterday by King’s son, Martin Luther King III. Mr. Edwards sat in the second pew with his wife, Elizabeth, directly in front of Senator Schumer. Mr. Schumer has already said he would endorse Mrs. Clinton if she runs.

In addition to his comments on the war, Mr. Edwards also condemned the income gap between the rich and poor in America and said the nation must become less dependent on fossil fuels.

Last night’s event at Riverside Church kicked off a series of events honoring King throughout the city today. Mayor Bloomberg is speaking at a number of events, including the annual forum at Rev. Al Sharpton’s National Action Network in Harlem.