Obama would restrict NASA's budget to last year's levels, USD18.7 billion annually through fiscal 2016. The figure represents a 1.6-per cent decrease from the spending total the agency had sought for fiscal 2011, which ends in September.
"This budget requires us to live within our means so we can invest in our future," NASA Administrator Charles Bolden told a news conference.
Bolden sought to put a brave face on the budget limitations, saying the administration's proposal "maintains our commitment to human spaceflight" and research.
Experts said it reflected Washington's new fiscal reality, framed by voter frustration with excessive government spending.
"There is not a lot of money available," said John Logsdon, a former director of the Space Policy Institute in Washington.
"It should not compromise what NASA wants to do but it certainly would slow it down," said Logsdon, an independent consultant to the Obama administration.
The belt-tightening comes just as the United States winds down its space shuttle program, and struggles to move forward on a replacement for the vaunted vessels that have carried hundreds of astronauts into space.
Nearly half of Obama's proposed 2012 NASA budget -- and for the next five years -- is dedicated to space operations and exploration systems, including USD2.9 billion for the development of a heavy launcher and a space capsule intended for missions beyond low Earth orbit.
Seven billion dollars have been earmarked for work aimed at making the new heavy launcher operational by 2016. It will be crucial for sending astronauts beyond low Earth orbit to an asteroid and to Mars.
NASA has not yet determined the architecture of the system nor when it will be operational.
Obama's budget would continue to push for commercial partnerships to develop reliable access to the space station and lessen the reliance on Russia, whose Soyuz spacecraft will be carrying US astronauts to the ISS until a shuttle successor is developed.
The draft budget proposes 850 million dollars in 2012 as seed money to help companies like SpaceX -- which has already successfully launched a prototype space capsule into orbit.