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April 22 (Reuters) - Tesla TSLA.O CEO Elon Musk said on Tuesday he will cut back his work for President Donald Trump to a day or two per week starting sometime next month, after the billionaire's aggressive cost-cutting tactics sparked public backlash and investor concern.

Musk's 130-day mandate as a special government employee in the Trump administration is set to expire around late May.

"I think starting probably next month, in May, my time allocation to DOGE will drop significantly," Musk told investors on a conference call after the electric car marker reported results that topped Wall Street's rock-bottom expectations.

Tesla has faced a troubling few months as deliveries of its aging lineup of electric vehicles have nosedived, Musk's political activities have drawn protests, and its stock has nearly halved from its December peak. Many investors had been calling for Musk to leave his work as Trump's adviser and manage Tesla more closely.

Musk said the major work setting up his cost-cutting Department of Government Efficiency initiative was done.

Under Musk's leadership and with the stated aim of increasing efficiency, DOGE staff upended agencies in a sweeping restructuring that has challenged congressional authority and faced a series of lawsuits.

Musk, the world's richest person, has defended his role as an unelected official who was granted unprecedented authority by Trump to dismantle parts of the U.S. government.

As of Tuesday, DOGE estimated on its website that it has saved U.S. taxpayers some $160 billion. However, the group's calculations have been rife with errors, corrections and incomplete explanations.

(Reporting by Alexandra Ulmer in San Francisco, additional reporting by Akash Sriram; Editing by Scott Malone and Lisa Shumaker)

((peter.henderson@thomsonreuters.com; +1 323 251 4827))