The Justice Department acknowledged yesterday it has begun a preliminary inquiry into minority employment practices in the Fairfax County government, but took pains to distinguish the probe from an "investigation."

"We received information about the Fairfax government we felt should be checked out," said John V. Wilson, assistant director of public information in the Justice Department.

Wilson said the inquiry "is just not what we consider an investigation." That would come, he said, if the inquiry indicates the possibility of violations - "and at this point we're not even thinking about possible violations."

Fairfax officials, led by County Executive Leonard Wharton, met with Justice Department attorneys yesterday. County officials gave the attorneys a copy of Fairfax's new affirmative action goals.

The program. adopted after a heated debate that split the nine-member Board of Supervisors, calls for hiring members of racial minorities for 40 per cent of the 325 county government jobs expected to be filled in 1978. Four supervisors who opposed specific goals abstained from the final vote on the plan, which passed 5 to 0.

While many blacks and other members of minority groups are employed by the county government, most occupy the lowest positions, such as in maintenance. Whites fill all but two of the 71 positions in the top ranks of officials and administrators.