Federal agencies are investigating reports that Rockwell International's Space Systems Group begam in 1977 and hide cost overrun on the National Aeronautics and Space Administration's giant space shuttle project and another contract for the Air Force, it has been learned.

This was done, several present and former Rockwell employes said in interviews, by having some employes charge certain expenses to other projects.

NASA's Inspector General's Office and the Department of Defense have launched an investigation of the reported practices, which, if true, may have contributed to delays in acknowledging cost overrun on the space shuttle. Although NASA officials were told of the situation in 1977, NASA only recently admitted that the space shuttle would be at least $500 million over budget.

Certain jobs on the Navstar satelite project for the Air Force were charged to the space shuttle contract, while development work on the multibillion-dollar space shuttle partly was hidden in later production budgets, according to present and former employes who have provided company documents to back up their contentions.

Rockwell officials have achnowledged that an investigation is going on but have refused to comment.

Among the contentions raised by the workers:

In 1977 and 1978, some employes were instructed to fill out some time cards as if they were working on the shuttle, while they actually were working on the Navstar satellite system: Curent work on the Navstar system also was charged to future operations, a procedure that violates government budget rules.

During the same period, funds from later stages in the space shuttle construction project were used to pay for current development work, leaving the future budgets depleted.

When one shop manager, Ray Sena, refused to participate and complained to higher management and NASA officials, he was formally suspended by Rockwell.