The budget proposed Monday by US President Barack Obama for fiscal year 2013 would slash $226 million from the US space agency's Mars exploration program, likely axing a planned partnership with Europe.

While the overall proposal is to give NASA $17.7 billion, a decrease of 0.3 percent or $59 million less than 2012, the steepest cuts -- a near 39 percent decline -- hit plans for robotic exploration of Mars.

The budget did not specifically mention the ExoMars collaboration with the European Space Agency, which was to send an orbiter to the red planet in 2016 followed by a pair of rovers in 2018 ahead of plan to return samples to Earth in the 2020s.

However, scientists familiar with the proposal have said the level of financial cuts would likely spell the end of the NASA-ESA deal.

The president's budget said that "support for robotic exploration of Mars is reduced following the launch in 2012 of the multi-billion dollars Mars Science Laboratory," a sophisticated rover nicknamed Curiosity that should land on the red planet in August.

"NASA remains interested in working with international partners to identify opportunities to cooperate in Mars exploration consistent with the budgets available to the agencies," it said.

"Some important, but currently unaffordable mission are deferred, such as large scale missions to study the expansion of the universe and to return samples from Mars."

According to the deal NASA and ESA made in 2009, NASA would have contributed $1.4 billion to the project and ESA would have chipped in $1.2 billion.

Other main features of the president's proposal for the US space agency include funding for the elaborate James Webb Space Telescope, which appeared in peril last year, while urging the project be capped at eight billion dollars.

The project to build the world's most powerful telescope, 100 times more sensitive than its predecessor the Hubble space telescope, was on track to launch in 2018 at a total project cost of $8.8 billion, NASA said in December after a series of delays and cost overruns.

NASA would also get three billion dollars for developing new spacecraft and rockets to take the next generation of astronauts to space, after the space shuttle program ended last year leaving Russia as the sole taxi to the International Space Station.

Big projects include $1.86 billion for the continued development of a Space Launch System (SLS) heavy lift rocket and $1.2 billion for the Multi-Purpose Crew Vehicle to "with a key initial goal of visiting an asteroid next decade," it said.

Other efforts to streamline operations at the space agency would bring $200 million in savings.

The budget comes as Obama is seeking re-election and it is widely regarded in Washington as a partisan document that has little chance of being voted into law.

Democrats in the Senate say that they will not bring it up for a vote because the government is already financed through the next year on the basis of a spending agreement reached with Republicans in September.