WASHINGTON — In his first seven months on the job, NASA Administrator Michael Griffin has announced the replacement of eight of the agency's 14 top career civil servants, a mass beheading seldom seen in a city where the political folks are the ones who routinely get the ax.

Griffin is getting away with it because, unlike most new agency chiefs, he is not a stranger who arrived in town with a couple of trustworthy sidekicks, a head full of big ideas and no idea how to implement them.

The ideas are big enough: Griffin seeks nothing less than the transformation of NASA from an agency focused for 25 years on the space shuttle and the international space station to an enterprise rebuilt to implement President Bush's call to return humans to the moon by 2020 and eventually send them to Mars.

But Griffin, 56, brings more to the job than vision. A blunt scientist-engineer with 35 years in the aerospace business, he also has worked at NASA, the Defense Department and as a consultant and expert frequently summoned by Congress to testify on the shortcomings of the agency he now leads.

"I say this with all humility," Griffin said. "I don't believe there is someone else who knows the broad span of NASA better than I. ... When I was offered the job, I showed up at the front door knowing what needed to be done. I did not want to waste any time, nor did I feel I needed to."

And he didn't. Two months after his April 13 confirmation, all four of NASA's mission directors, in charge of human space travel, science, aeronautics and exploration, announced their departures. Also leaving are four of 10 directors of the agency's major installations, among them Houston's Johnson Space Center.

"It's a rare moment when you get a housecleaning like this," said New York University's Paul Light, an expert on the federal bureaucracy. "It could presage a strong turnaround for an agency that's been adrift for years if not decades."

Griffin hopes so: "I don't share the view that a good manager is a good manager is a good manager," he said. Instead, he wants an old-style NASA leadership steeped in technical and scientific know-how.

"To do this, you do need to be a rocket scientist," Griffin said. "The managers we had in place were not in my judgment what we needed for the change of direction we wanted to take."

Besides bringing technical expertise, Griffin has revamped the National Aeronautics and Space Administration's chain of command by swapping out his deputy administrator and chief of staff — both political positions — and putting a civil servant into the new job of associate administrator, who oversees NASA's day-to-day operations.

His model, he said, is the triumvirate that ruled NASA during the run-up of the Apollo program in the early 1960s. "It was the best NASA ever," Griffin said.