An artist's impression of the asteroid Apophis.
NASA wants to grab a small asteroid and tow it into orbit around the moon, as part of a long-range plan to establish permanent manned outposts in space, a US senator said.
Senator Bill Nelson said that to get the project off the ground President Barack Obama will propose funding for the US space agency of about $US100 million ($96 million) in his 2014 budget, which he submits to Congress on Wednesday.
''This is part of what will be a much broader program,'' the Florida Democrat said.
''It combines the science of mining an asteroid, along with developing ways to deflect one, along with providing a place to develop ways we can go to Mars.''
The plan calls for a robotic spacecraft to capture the asteroid and tow it back towards Earth, ultimately leaving it in a stable orbit around the moon, close enough that, within eight years, astronauts could go there.
A similar plan was initially proposed last year by experts at the California Institute of Technology, and the group, with other researchers in the field, have prepared a detailed study into the project's feasibility.
''It would be mankind's first attempt at modifying the heavens to enable the permanent settlement of humans in space,'' the scientists said.
Mr Obama's goal of sending a manned mission to a near-Earth asteroid by 2025 is impossible given NASA's present and projected funding levels, expert analysis has suggested.
But using an unmanned vehicle to bring a 500-tonne asteroid close to Earth could get humans to an asteroid as early as 2021, four years before the deadline.
Once in place, ''there could be mining activities, research into ways of deflecting an asteroid from striking Earth, and testing to develop technology for a trip to deep space and Mars'', Senator Nelson said.