WASHINGTON — House appropriators kicked off budget hearing season on Feb. 29 by grilling U.S. President Barack Obama’s science adviser about proposed cuts to NASA’s Mars exploration program.

Some members of the House Appropriations commerce, justice, science subcommittee indicated they would seek to restore Mars funding when the panel begins drafting NASA spending legislation.

Chief among these was the subcommittee’s ranking Democrat, Rep. Chaka Fattah of Pennsylvania. Fattah said he had “concerns about what we’re going to do relative to planetary science and Mars.

“I understand the budget constraints, but I think this is something the committee will continue to explore with you about what can be done,” Fattah told John Holdren, director of the White House Office of Science and Technology Policy and sole witness at the hearing.

The subcommittee’s chairman, Rep. Frank Wolf (R-Va.), questioned Holdren at length about whether the cuts to the Mars program would erode NASA’s ability to conduct robotic landings throughout the solar system. However, Wolf took no position on restoring the funds the White House seeks to delete from the Mars program.

Holdren said he regretted the cuts, but the Mars program NASA had been planning was incompatible with the current constrained budget environment and the compromise reached last year between Congress and the administration on NASA’s top priorities: the heavy-lift Space Launch System and its companion crew capsule; the James Webb Space Telescope; and the Commercial Crew Program, which seeks to develop privately owned astronaut taxi systems to restore independent U.S. access to the international space station by 2017.

“Finding the money to advance those programs within an obviously limited total did require cutting back on some things that, in better times, we would like to continue to do,” Holdren said. “I wish it were otherwise.”

Under Obama’s 2013 spending proposal, NASA’s budget would drop to $17.71 billion in October, a 0.3 percent cut compared with the current fiscal year.

Spending on Mars exploration, however, would drop 40 percent compared with 2012, leaving NASA’s Planetary Science Division with $360 million on its portfolio of robotic Mars missions.

When the budget proposal was released in mid-February, NASA officially called off its participation in an international Mars sample-return project and announced it would start planning a more modest stand-in mission that would launch in 2018 or 2020.

The Obama administration’s plan to shrink the Mars program drew the immediate ire of a  House appropriator whose California congressional district includes the Jet Propulsion Laboratory — NASA’s lead center for robotic Mars missions.

“I am determined to fight this tooth and nail,” Rep. Adam Schiff (D-Calif.) said. “Cannibalizing the Mars program … is a huge step backwards for NASA.”

Much of the money diverted from the Mars program in the White House’s 2013 NASA budget would be  used to cover a 21 percent increase for the $8.8 billion James Webb Space Telescope (JWST). The U.S. Government Accountability Office, in a report released March 1, blamed JWST’s cost growth for forcing NASA’s withdrawal from Europe’s 2016 and 2018 ExoMars missions. The report noted that JWST’s $3.6 billion in cost growth since 2009 exceeds the combined life-cycle costs of the seven smallest projects included in the Government Accountability Office’s annual review of NASA missions costing at least $250 million.

Schiff, who has served on the House Appropriations Committee since 2007, defended JWST as recently as last fall, when he opposed Wolf’s proposal to cancel the project.

But with the Mars program and other Jet Propulsion Laboratory-led initiatives facing major cuts Schiff has changed his tune.

“Mr. Chairman, I have to tell you, you were absolutely right last year when you expressed concern that James Webb would, among other things, cannibalize everything else,” Schiff said at the hearing. “You were absolutely, absolutely right.”

Holdren reminded the subcommittee that JWST, like the Mars program, “is ranked very highly by a large part of the science community.”

Moreover, Holdren said, budget pressures are unlikely to relent, and funding for NASA is bound to remain tight for years.

In that environment, he said, “if you want to fix planetary science, you have to figure out where it’s going to come from, and somebody’s ox is going to get gored.”

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.