Members of Congress say they've urged NASA to spare planetary science funding and resist pressures to make disproportionate cuts to the science budget.

In a letter to NASA Administrator Charles Bolden, U.S. Rep. Adam Schiff, D-Calif., and Sen. Dianne Feinstein, D-Calif., urged the space agency to protect the funding for missions to Mars and the outer planets allocated by Congress this spring.

"While we fully understand that the funding levels ... are subject to change to reflect across-the-board and sequester cuts, we expect that the balance among programs will remain consistent with the structure directed by Congress," they wrote.

NASA will have to move some money around to make up for shortfalls related to the automatic federal budget cuts that went into effect earlier this year.

Schiff, whose district includes NASA's Jet Propulsion Laboratory in Pasadena, said the science funding could possibly see reductions in the space agency's new operating plan.

"We're hearing disturbing sounds that they're going to raid planetary science, and seriously degrade Mars missions -- even though sample return is the highest priority" of the official plan for scientists in the field, he told the Los Angeles Times.

Schiff expressed concern taking money away from ongoing, high-priority science projects could hamper institutions such as JPL in their efforts to hold on to experienced staff for future missions.

"We lose the people who have the ability to land on the martian surface," he said. "It's a unique skill set. We're the only people who can do this. We don't want to be led on by NASA setting up the mission and then setting it up to fail."