A congressional committee promised Thursday to scrutinize NASA and its spending as the agency proceeds with a program to take astronauts to the moon and Mars.

The space agency faces hidden costs by starting development of the spacecraft and rockets for the program without knowing the price tag of the new technology, a watchdog official warned Thursday in Washington at a hearing of the House Committee on Science.

“When you don’t abide by those particular principles _ which is not going beyond what your knowledge tells you _ then you do run into trouble,” said Allen Li, director of acquisition and sourcing management for the Government Accountability Office.

The committee held the hearing in response to a report the GAO released last July that raised concerns about the affordability of developing the Orion manned lunar vehicle and the Ares 1 and 5 rockets. The committee took no action but members promised to monitor NASA closely.

The report said that developing Orion, the rockets and robotic missions to the moon would cost $230 billion over two decades, and that those efforts likely would face a budget shortfall of more than $18 billion through 2025.

But Scott Horowitz, a NASA associate administrator, said he was confident the space agency would finish developing the spacecraft and rockets on time and within cost.

The price will be kept down because of the design simplicity of the spacecraft and rockets, which use technology from the Apollo era 40 years ago, Horowitz said.

Orion will cost $200 million a flight, said Horowitz, although Li said the figure wouldn’t be known accurately until 2008.

Horowitz stressed the importance of stable funding in keeping costs down. NASA wants to begin flying Orion with astronauts by 2014 and return to the moon no later than 2020.

“If you short-fund the program in the near term, you can guarantee that you will stretch it out and increase its costs in the long term,” Horowitz said.

NASA this month picked Lockheed Martin Corp. to build the manned lunar spaceship. The contract is worth $8.1 billion through 2019.

In response to the GAO report, NASA made some changes to limit its obligations to the projects if they don’t succeed, but Li said the space agency needs to go further.