WASHINGTON — U.S. President Barack Obama’s $18.7 billion budget request for NASA in 2012 sets the stage for a showdown with U.S. lawmakers, who last fall approved a hotly debated but ultimately bipartisan authorization bill that recommends $19.5 billion for NASA next year including $4 billion for a new heavy-lift launch vehicle and crew capsule Congress says the agency must build by 2016.

Obama administration officials said the 2012 spending plan delivered to Capitol Hill Feb. 14 makes tough choices, supporting elements of the three-year NASA Authorization Act of 2010 while conforming to a top-line spending freeze that is roughly $750 million less than the law recommends next year. While the president’s plan provides less funding for the new rocket and spacecraft than called for in the law, spending on commercial space, technology research and climate initiatives central to Obama’s vision for the agency would still see a boost in his 2012 budget.

NASA Administrator Charles Bolden acknowledged that some members of Congress will not like the plan but said during a Feb. 14 news conference that it “keeps our faith” with the NASA authorization bill Obama signed into law last October.

“Most members of Congress, while not happy, understand that the budgets for everything had to come down, and NASA is no different,” Bolden said during the news conference, referring to increasing pressure on the White House to reduce the nation’s budget deficit by lowering federal discretionary spending.

Bolden said Obama’s decision last year to continue U.S. participation in the international space station through at least 2020 means the agency must invest heavily in private space companies to ensure U.S. access to the orbiting outpost following retirement of NASA’s space shuttle fleet later this year.

“If I want to sustain [the space station], have it safe for crews, I need to have a way to get cargo and crew there as quickly as we can,” Bolden said, adding that once the shuttle retires, NASA will rely on Russian rockets and spacecraft for crew access to the space station before a commercial domestic capability becomes available around mid-decade. “With that goal in mind, we changed the balance of funding to commercial crew and the vehicles themselves,” he said.

As such, commercial spaceflight is a clear winner in Obama’s 2012 NASA budget blueprint, which calls for spending $350 million more than the $500 million Congress authorized for such initiatives next year.

Helping to fund that increase is some $2.4 billion in anticipated savings from the retirement of the space shuttle, a program that consumed more than $3 billion of the $18.72 billion Congress appropriated for NASA in 2010.

Savings from the shuttle fleet’s retirement also are offset in next year’s spending plan by increases to other Obama priorities, including research the president says could seed game-changing technologies in support of exploration missions and climate-monitoring initiatives that support his environmental policy agenda.

To boost funding for the president’s priorities and still stay within a constrained top-line budget, the plan dials back spending on development of hardware needed to conduct human exploration beyond low Earth orbit. Much of the work was started under the Moon-focused Constellation program, which Obama sought to terminate but was partially rebuffed by Congress.

Although the 2010 NASA Authorization Act does not specify the Moon as the ultimate destination for manned space exploration, it directs the agency to leverage Constellation and space shuttle investments in developing the heavy-lift rocket and crew capsule. However, NASA said in a Jan. 10 report to Congress that the cost and schedule laid out in the law for developing the new vehicles were unrealistic.

During a Feb. 16 House Science, Space and Technology Committee hearing, White House science adviser John Holdren defended the president’s NASA proposal, saying the administration is doing its best to comply with goals outlined in the authorization act, according to a Feb. 16 committee news release.

“When pressed on whether the goals in the bill will be achieved, Dr. Holdren conceded, ‘We will try,’” the news release states.

But some lawmakers said the budget plan does not comply with the law.

“In this time of necessary budget cuts, NASA does well compared to most other agencies,” Sen. Bill Nelson (D-Fla.), chairman of the Senate Commerce science and space subcommittee and the primary architect of the authorization act, said in a Feb. 14 statement. “But the president’s budget does not follow the bi-partisan NASA law Congress passed late last year. The Congress will assert its priorities in the next six months.”

Rep. Pete Olson (R-Texas), an outspoken critic of Obama’s vision for NASA, blasted the president’s plan for boosting funds for Earth science and commercial space initiatives.

“This budget ignores the human space flight priorities outlined by Congress last year,” he said in a Feb. 14 statement in which he argued for shifting funds from NASA’s Earth science coffers to pay for manned space exploration. “This plan will ensure that NASA can achieve the goals set by Congress in a fiscally responsible manner.”

NASA officials point out that funding for the heavy-lift rocket and spaceship is on par with the $2.75 billion Congress authorized for the efforts in 2011.

“These are difficult fiscal times and we have long-term challenges that will not be addressed in any single fiscal year,” Bolden said during the press conference, noting that Congress has yet to approve a 2011 spending package for the federal government, leaving NASA and most other agencies operating in the current budget year at 2010 funding ceilings.

As lawmakers continue to debate 2011 appropriations, NASA could be in store for a significant funding cut this year if Congress approves in its current form a continuing resolution drafted by Republican House leaders that would fund the government through the remaining seven months of fiscal 2011. The bill, H.R. 1, proposes lowering NASA funding by about $600 million from the $18.72 billion Congress appropriated for the agency in 2010.

Obama has threatened to veto the measure, which more broadly proposes $100 billion in federal funding cuts through Sept. 30. But in his 2012 spending plan, the president yielded to pressure from Republican lawmakers to curb spending, proposing a five-year funding freeze at 2010 levels for most non-security discretionary agencies, including NASA.

“These are really difficult fiscal times,” Bolden said during the budget rollout. “There is no question that we can do it, we’ve just got to make very difficult decisions, and that’s what you see in this budget.”