WASHINGTON  As foreign investors once again try to buy American industrial assets, the Obama administration is grappling with how to protect national security while promoting economic recovery.

In recent days, the administration has threatened to block the proposed takeover by the Chinese government of a tiny Nevada gold mining company, according to executives for the company, Firstgold.

Administration officials have also raised questions about a bid by a United Arab Emirates-controlled company to buy a large stake of Virgin Galactic, which is trying to build the world’s first commercial carrier to take tourists into space.

The issues involved are serious enough that the companies involved in the Virgin Galactic deal have agreed to withdraw the application to provide more time for them to be addressed.