FORT WORTH  Brigitte Gabriel bounced to the stage at a Tea Party convention last fall. She greeted the crowd with a loud Texas “Yee-HAW,” then launched into the same gripping personal story she has told in hundreds of churches, synagogues and conference rooms across the United States:

As a child growing up a Maronite Christian in war-torn southern Lebanon in the 1970s, Ms. Gabriel said, she had been left lying injured in rubble after Muslims mercilessly bombed her village. She found refuge in Israel and then moved to the United States, only to find that the Islamic radicals who had terrorized her in Lebanon, she said, were now bent on taking over America.

“America has been infiltrated on all levels by radicals who wish to harm America,” she said. “They have infiltrated us at the C.I.A., at the F.B.I., at the Pentagon, at the State Department. They are being radicalized in radical mosques in our cities and communities within the United States.”

Through her books, media appearances and speeches, and her organization, ACT! for America, Ms. Gabriel has become one of the most visible personalities on a circuit of self-appointed terrorism detectors who warn that Muslims pose an enormous danger within United States borders.

Representative Peter T. King, Republican of Long Island, will conduct hearings Thursday in Washington on a similar theme: that the United States is infiltrated by Muslim radicals. Mr. King was the first guest last month on a new cable television show that Ms. Gabriel co-hosts with Guy Rodgers, the executive director of ACT! and a Republican consultant who helped build the Christian Coalition, once the most potent political organization on the Christian right.