The American Jewish Committee, an ardent defender of Israel, is known for speaking out against anti-Semitism, but this advocacy group has recently stirred up a bitter and emotional debate with a new target: liberal Jews.

An essay the committee features on its Web site, ajc.org, titled “ ‘Progressive’ Jewish Thought and the New Anti-Semitism,” says a number of Jews, through their speaking and writing, are feeding a rise in virulent anti-Semitism by questioning whether Israel should even exist.

In an introduction to the essay, David A. Harris, the executive director of the committee, writes, “Perhaps the most surprising — and distressing — feature of this new trend is the very public participation of some Jews in the verbal onslaught against Zionism and the Jewish State.” Those who oppose Israel’s basic right to exist, he continues, “whether Jew or gentile, must be confronted.”

The essay comes at a time of high anxiety among many Jews, who are seeing not only a surge in attacks from familiar antagonists, but also gloves-off condemnations of Israel from onetime allies and respected figures, like former President Jimmy Carter, who titled his new book on the Mideast “Palestine Peace Not Apartheid.” By spotlighting the touchy issue of whether Jews are contributing to anti-Semitism, both admirers and detractors of the essay agree that it aggravates an already heated dispute over where legitimate criticism of Israel and its defenders ends and anti-Semitic statements begin.