WASHINGTON — U.S. President Barack Obama’s $18.7 billion budget blueprint for NASA in 2012 was sharply questioned by a top appropriator in the U.S. House of Representatives who said it neglects to robustly fund development of new space exploration hardware mandated in two congressional acts.

During a May 3 hearing of the House Appropriations commerce, justice, science subcommittee, Rep. Frank Wolf (R-Va.), who chairs the panel, said Obama’s attempt to scrap NASA’s Moon-bound Constellation program in favor of investing in privately developed space taxis and cutting-edge technology was “soundly repudiated by Congress,” which has since adopted legislation directing the agency to salvage much of the scuttled program to develop a heavy-lift Space Launch System and Multi-Purpose Crew Vehicle.

“It seemed like the administration didn’t learn its lesson, though, because this year’s NASA budget is also unacceptable,” Wolf told White House science adviser John Holdren, who defended the budget request for NASA and other civil research and development agencies at the hearing. Wolf accused the White House of short-changing the heavy-lift rocket and crew capsule in its 2012 budget blueprint to cover increases in Earth science, space technology and commercial spaceflight.

“Why does the administration insist on using the exploration program as a bank to pay for the other priorities?” Wolf asked.

Holdren disagreed with Wolf’s characterization. “I wouldn’t phrase it quite that way,” he said.

Holdren stressed that the president’s budget still funds key ingredients of the space exploration hardware mandated in the 2010 NASA Authorization Act. The law directs NASA to spend $4 billion next year — $1.2 billion less than the president requested — on the crew capsule and heavy lifter ultimately capable of delivering 130 tons to low Earth orbit.

However, “if we want to maintain access for U.S. astronauts to the $100 billion international space station on U.S. rockets, if we want to minimize the gap during which we would be dependent entirely on the Russian Soyuz, we absolutely have to make investments in commercial crew development,” he said. With the space shuttle slated to retire this year, NASA plans to rely on Russia to deliver crews to the orbiting outpost until privately developed rockets and spacecraft come on line later this decade.

“At the same time we need to invest in those technologies, the heavy lift and the crew capsule, to be ready for the next step, and there’s a balancing act involved in doing that under a budget cap that is lower than what one would want to pursue all those goals,” he said.

Holdren attributed NASA’s slow start on the Space Launch System to a prohibition on canceling Constellation and initiating new programs that was contained in last year’s appropriation. That prohibition was lifted in April.

“By the time we were relieved of that constraint, you weren’t in the same position that you would have been in if throughout fiscal year 2011 you had more flexibility,” Holdren said.

Wolf cited new language in a continuing resolution enacted in April — which funds the federal government for the remainder of 2011 — that directs immediate development of the 130-ton heavy-lift rocket and space capsule. The measure included $3 billion for both the rocket and crew capsule.

“Do you view the lift capability requirement as legally binding?” Wolf asked.

Holdren said the Obama administration is legally obliged to pursue the requirement, though whether or not NASA has a realistic shot at attaining the goal by the 2016 date directed in the authorization act remains to be seen.

“I don’t think we can necessarily legislate success,” he said. “Ultimately we will get 130 metric tons, whether we will get it by the date in the legislation, that’s something we are obliged to do and we will try to do it. Sometimes what the Congress wants, however admirable, is not necessarily achievable under the available budgets, and in the time available. So we’re going to try … but it’s going to be a challenge.”

Asserting that the administration would prefer to build a less-capable rocket, Wolf asked what kind of deep space exploration payload could be launched on a vehicle capable of placing 70 to 100 metric tons into orbit.

Holdren said the question was beyond his level of expertise. But he speculated that such an intermediate step would prepare the way for the larger lift capability and said a capable deep space exploration vehicle could be launched in sections on the multiple smaller rockets and assembled on orbit.

Wolf also questioned why the administration is not requesting a budget increase for NASA. “How does a flat NASA budget reflect an administration’s emphasis on scientific investment?” he said.

Holdren said he would have preferred to see a bigger budget for NASA.“Unfortunately at this particular juncture there’s not enough money and some difficult choices have been made,” he said.

Unmoved, Wolf said other federal research and development agencies saw increases while NASA’s budget was flat-lined, “and that just doesn’t make any sense.”