The Republican lawmaker who convened a much-anticipated hearing on the problem of radicalization among American Muslims - lambasted by critics as a revival of McCarthyism - opened the session on Thursday by vowing to continue with his inquiry, saying that "to back down would be a craven surrender to political correctness."

The lawmaker, Representative Peter T. King, who is chairman of the House Homeland Security Committee and represents parts of Long Island, said there was "nothing radical or un-American" in the hearings.

"Indeed, Congressional investigation of Muslim American radicalization is the logical response to the repeated and urgent warnings which the Obama administration has been making in recent months," he said in his opening statement.

Mr. King quoted top Obama administration officials as attesting to the threat of homegrown terrorism, listing a half-dozen American citizens and residents accused of plotting or carrying out violence in the name of Islam since 2009.

But the committee's top Democrat, Representative Bennie Thompson of Mississippi, said Muslims as a community should not be accused of radicalism or violence. He suggested that such accusations could play into the hands of Al Qaeda by supporting its claim that the United States is hostile to Islam.