1:50 PM PT -- Harvard University announced that they've appointed Alan Garber as the new interim president.

Claudine Gay is stepping down as Harvard President after waffling on the issues of Jewish genocide and antisemitism, and being dogged by allegations of plagiarism.

Gay plans to resign Tuesday afternoon, according to the Harvard Crimson -- the university's student-run publication -- which cites a "source with knowledge of the decision."

Gay's resignation ends her Harvard presidency after just 6 months and 2 days ... the shortest in the Ivy League school's history.

Remember, Gay was among the university presidents who testified on Capitol Hill last month and refused to answer a yes or no question about whether "calling for the genocide of Jews" violated Harvard's rules.

The ensuing controversy already lead to former University of Pennsylvania president Liz Magill's resignation ... and now Gay is following suit.

In addition to her controversial congressional testimony, Gay also faced several allegations of plagiarism in her work as a scholar.

Gay's resignation comes just 3 weeks after the Harvard Corporation unequivocally said it was backing her. Apparently, Harvard's head honchos had a change of heart.

It's unclear who will replace Gay as Harvard's president.