NASA's decision to postpone pressurizing the fuel tanks aboard the Mars Observer may have led to a fuel line break that doomed the $500 million space mission, The Washington Post reported Monday.

Instead of pressurizing the propellent tanks five days after launch as originally planned, managers decided to wait 11 months until the observer reached Mars, the Post said.The decision was made seven months before the September 1992 launch, it said.

The decision to postpone pressurization was an effort to prevent potentially serious leaks in the tanks, the newspaper said, but valves were not replaced to reflect the changed conditions, and the probable result was a catastrophic rupture in a fuel line that spun the spacecraft out of control.

No one at the National Aeronautics and Space Administration's Joint Propulsion Laboratory in Pasadena, Calif., or elsewhere questioned the decision, the Post said.

It quoted Glenn E. Cunningham, the Mars Observer project manager at the lab, as saying: "With benefit of 20-20 hindsight, it appears that probably all of us did not do as much analysis on this new condition as probably should have been done."

The investigative panel said the most likely cause of the spacecraft's disappearance last Aug. 21 was a "massive failure" in the pressurization component of the propulsion system.