SAN FRANCISCO, March 26 (Reuters) - Two U.S. senators on Thursday planned to introduce a bill that would ban the government from buying or operating humanoid robots made by Chinese firms.

Tom Cotton of Arkansas, the third most-powerful Republican in the Senate, and Chuck Schumer of New York, the top Democrat in the chamber, plan to put forward the American Security Robotics Act, which would prohibit the federal government from buying or using unmanned ground vehicles made by adversaries such as China and bar the use of federal funds in connection with the robots.

The bill comes as Chinese firms compete with U.S. firms such as Tesla to deliver humanoid robots that can stand in for humans for tasks as varied as dangerous manufacturing work and household chores. At least two Chinese firms - Agibot and Unitree - are preparing to list shares in China this year as their products capture attention there.

In statements on Thursday, the lawmakers argued that such robots present a national security risk because they could be used to gather data to send back to China or could be remotely controlled from China. A group of lawmakers last year urged the Pentagon to add Unitree to a list of firms that work with China's military.

"Robots made by Communist China threaten Arkansans' privacy and our national security," Cotton said.

Schumer said Chinese firms with support from the Chinese Communist Party "are running their standard playbook - this time in robotics - trying to flood the U.S. market with their technology, which presents real security risks and threats to Americans' privacy and American research and industry."

The bill would contain exemptions for the U.S. military and law enforcement agencies to research Chinese robots, as long as the robots cannot transmit data to or receive data from China.

In the U.S. House of Representatives, Representative Elise Stefanik, a New York Republican, on Thursday planned to announce a companion bill to the Senate version.

"We must continue to promote and propel America's robotics superiority while safeguarding our privacy and national security from adversaries," Stefanik said in a statement.