WASHINGTON - The White House on Sunday praised American Muslims for helping fight violent extremism, but a House leader on terrorism issues said they aren't co-operating enough with law enforcement to counter the radicalization of young followers by al-Qaida-linked groups.

Deputy National Security Adviser Denis McDonough, speaking at an interfaith forum at a Northern Virginia mosque, commended its members for taking "an unequivocal stand against terrorism."

"You've sent a message that those who perpetrate such horrific attacks do not represent you or your faith, and that they will not succeed in pitting believers of different faiths against one another," McDonough said.

But Rep. Peter King, chairman of the House Homeland Security Committee, re-asserted warnings about al-Qaida terrorists targeting Muslim youth in this country.

"The overwhelming majority of Muslims are outstanding Americans, but at this stage in our history there's an effort ... to radicalize elements within the Muslim community," he said in a preview of his hearing Thursday on the extent of the problem and the Muslim community's response.

"It's there and that's where the threat is coming from at this time," King said in an interview broadcast Sunday.

"I don't believe there is sufficient co-operation" by American Muslims with law enforcement, King said. "Certainly my dealings with the police in New York and FBI and others say they do not believe they get the same -- they do not give the level of co-operation that they need."

In New York City, a coalition of over 100 interfaith, non-profit and governmental organizations planned a rally Sunday against King's hearing, saying it will send the wrong message to U.S. Muslims by "demonizing" them. The committee hasn't released a witness list yet for the hearing.

The administration has tried to strike a balance on the thorny issue, working to go after homegrown Islamic extremists without appearing to be at war with the Muslim world. There has been an effort to build stronger relationships with Muslims -- internationally and with Islamic leaders in the United States.

At the same time, however, militant Islamic propaganda has factored into recent terrorist attacks and foiled attempts in this country.

Maj. Nidal Hasan, the suspect in 2009 shootings at Fort Hood, Texas, is believed to have been inspired by the Internet postings of violent Islamic extremists, as was Faisal Shahzad, who pleaded guilty to terrorism and weapons charges in the attempted car bombing in New York's Times Square.

The first Muslim elected to the House, Rep. Keith Ellison, said that while it's proper to investigate radicalization, he thinks it is wrong to single out one religion.

"To say we're going to investigate a religious minority, and a particular one, I think is the wrong course of action to take," said Ellison, a Minnesota Democrat. "I don't want them to be able to stand up and claim, you know, see, we told you, America is at war with Islam. That's one of their main recruiting arguments."

Ellison said Congress needs to be careful about how it addresses the issue in investigative hearings. Appearing with King on CNN's "State of the Union," he said it makes sense to speak with people in the Muslim community about efforts by extremists such as radical cleric Anwar al-Awlaki to encourage Muslims to wage attacks against the U.S.

But Ellison argued that Muslim-Americans have worked with authorities to report suspected terrorists within their community. It's important, he said, to engage Muslims, not frighten them.

Shortly after he took office, Obama pledged a new beginning in the U.S. relationship with the Muslim world. His national security strategy dropped rhetorical references to Islamic radicalism as Obama argued that words matter and such inflammatory language linking Islam to the terrorist threat feeds al-Qaida propaganda and could alienate moderate Muslims.

Others, however, say the administration is failing to clearly articulate the threat, and should more directly identify Islamic extremism as a root cause of terrorism.

"It's an international movement with elements here in the United States, and to me, that's a real distinction," King said. "There's always going to be isolated incidents, isolated fanatics, isolated terrorists even. But an organized terrorist effort, to me, is different, which requires an investigation unto itself."

The site for McDonough's speech was the All Dulles Area Muslim Society, one of the largest Muslim communities-mosque in the U.S., with seven branches serving more than 5,000 families, according to its website.

It is an outreach partner of the FBI and its executive director is a member of the Homeland Security Advisory Council's Countering Violent Extremism Working Group.