Cape Canaveral, Fla. ? NASA has too many astronauts waiting around for their chance to fly in space and needs to do a better job of matching the size of the corps to the number of missions, the agency’s inspector general said Thursday.

In a report that should have been released in February but was delayed because of the Columbia disaster, the inspector general’s office concluded the space agency was “overly optimistic” in predicting future shuttle flight rates and hired too many astronauts in recent years.

The report said because of an engineer shortage at Johnson Space Center in Houston, high-priced astronauts had been used to fill engineering positions. That practice may have been used, in turn, to justify the large size of the astronaut corps.

“We found that some astronauts worked in technical assignments that did not require astronauts and could have been performed by less expensive engineers,” the report said.

NASA has 144 astronauts on its payroll, about a third of whom have yet to fly into space. With the remaining three shuttles grounded in the wake of the Columbia accident, the rookies will have to wait much, much longer for a rocket ride.

The inspector general’s office did not call for any astronaut layoffs, suggesting only that NASA hire more judiciously.

NASA’s top spaceflight official has already concurred with the recommendations, and the space agency has agreed to better manage the size of its astronaut corps and establish formal criteria for giving technical assignments to astronauts.

The inspector general said Johnson Space Center could not determine the full cost of its astronaut corps.