More than two dozen Muslim American clerics and community leaders condemned Islamic terrorism at a crowded news conference in the District on Wednesday, denouncing the atrocities committed by the Islamic State in Iraq and Syria and calling on young Muslim Americans to resist the appeal of jihadist ideology.

The leaders, who were joined by several officials from the Department of Homeland Security, stressed that the great majority of Muslim Americans are loyal and peaceful citizens. They vowed to cooperate with law enforcement officials and to work to dissuade Muslim youths from following violent jihadi paths.

“Young people, please do not listen to this ideology,” said Mohammed Magid Dar, director of the All Dulles American Muslim Society in Sterling, Va., the largest mosque in the Washington region. “If someone asks you to join this cult or this group, resist the slogans that promise justice but carry out injustice.”

David Gersten, coordinator for countering terrorist extremism at the Department of Homeland Security, said Muslim American communities need to be the “front lines” against the blandishments of Islamist fighters trying to recruit youths to Islamic State’s cause, especially via social media.

It was the first time a U.S. official had appeared publicly with Muslim American leaders here. Officials of the Muslim Public Affairs Council, a national nonprofit advocacy group, organized the news conference and asked Homeland Security officials to attend.

The group’s declarations came hours before President Obama was scheduled to address the nation and lay out his strategy for combating the Islamic State. One speaker asked that the group be referred to as the “Anti-Islamic State” and noted that most of its victims are Muslims.

Others expressed condolences for the victims of the terror attacks of Sep. 11, 2011.

The news conference included a broad array of speakers, highlighting the growing concern among Muslim Americans that their communities will be tarred with the extremist brush amid reports of Western Muslims being recruited to fight with the Islamic State.

Using the acronym for a former name of the Islamic State, Faizal Khan, imam of the Islamic Society of America mosque in Silver Spring, said, “ISIS and al Qaeda represent a warped religious ideology. Either we reject this violence in the clearest possible terms, or we allow them to become the face of Islam and the world’s perception of us for years to come.”

Participants included Muslim immigrant leaders from Indonesia, Pakistan, Ethiopia, Sudan and Trinidad, as well as American converts. There are an estimated half-million Muslims of foreign origin living in the United States.

“We reassure our fellow Americans that we are an integral part of the American fabric,” said Mohsin Ali Khan, a Pakistani American and a leader of a mosque in McLean. “You can count on our cooperation and support” in combating Islamic terrorism, he said.

Speakers stressed that, in addition to cooperating with police and other officials, they were working with young people in their communities to make sure they do not fall prey to the lure of radical Islamic ideology. One cleric said it was crucial to identify potential young jihadists and convince them to abandon a “twisted” version of Islam.

The news conference was preceded by a recitation of the Pledge of Allegiance by three young Muslim American Boy and Girl Scouts. Organizers said many Muslim communities are organizing groups and meetings to talk with young people about the positive message of Islam and the danger of jihadist thought.

One speaker was Cardinal ­Theodore McCarrick, a former Roman Catholic archbishop of Washington. He called on members of all religions to “stand together against the evil” and destructive violence of such groups as the Islamic State.