Federal personnel director Donald Devine yesterday said that natural attrition--voluntary resignations and retirements--will enable the administration to knock out most of the 75,000 government job slots President Reagan wants to eliminate, so that very few people will be fired.

The problem is "highly manageable," Devine said at an informal news conference at the Office of Personnel Management. "We expect this to affect very few people very adversely."

Those unfortunate few most likely will include upper-level professionals with highly specialized skills that are no longer in demand, Devine said. On the other hand, he added, those with easily transferable skills will have no difficulty. "We can hire all the secretaries we can get hold of."

The president has exempted several agencies from major reductions in force (RIFs). These include the Defense Department, whose personnel levels have been increased, some units of the Veterans' Administration, the FBI, Immigration and Naturalization Service, State Department, Internal Revenue Service, Customs Bureau and Secret Service.

The problem will come when the attrition does not take place in the occupations or agencies where it is wanted. In such cases, the government's placement program will try to transfer people cut from one agency to other federal jobs, Devine said. These people will be given priority over new outside job applicants.

The 75,000 figure, to be reached as an average during 1984, includes those who will lose their jobs at agencies slated for termination, such as the departments of Energy and Education and the Community Services Administration.

After Defense and other exempted agencies are subtracted from the total federal work force, this leaves a pool of 620,000 workers from which the 75,000 must be cut, a reduction of about 12 percent. Spread over 2 1/2 years or so, that could easily be taken care of if the current rate of attrition, about 9 percent annually, is maintained, Devine said.

Devine also acknowledged that the attrition rate depends to a large extent on the state of the economy. People will not leave a federal job voluntarily if they can't get one in the private sector. The Reagan program, he said, "is designed to increase jobs in the private sector."