BERLIN — Defying calls by the opposition for his resignation, the German defense minister, Karl-Theodor zu Guttenberg, said Tuesday that he would hold on to his job despite his admission that he had submitted a faulty dissertation for his doctoral degree.

“I made serious mistakes,” he said Monday night at a campaign event for the Christian Democratic Union in Kelkheim, in the state of Hesse.

“Over the weekend I had another look at my doctorate thesis,” Mr. Guttenberg, 39, told the audience of around 600 conservatives. “I lost sight of the sources in one of two places. I wrote this piece of work myself and I stand by it, but I also stand by the rubbish I wrote.” He said he was giving up the title of doctor, calling the decision to do so “painful.”

Opposition political parties and several academics have accused Mr. Guttenberg of plagiarizing multiple sections of his dissertation for the Ph.D., which was conferred on him by the University of Bayreuth in 2007. Even the conservative newspaper Frankfurter Allgemeine Zeitung was stinging in its criticism of Mr. Guttenberg, accusing him of having “inflated” his résumé.