THE INDICTMENT of a sitting Cabinet secretary on criminal charges -- in itself unique in this country's history -- raises additional questions when it comes this close to a presidential election. Labor Secretary Raymond Donovan, who now stands charged on 137 counts of grand larceny and fraud in connection with a subway contract involving his construction firm, has in turn charged that the Bronx district attorney, an elected Democrat, was motivated by partisan considerations in timing the indictment.

Much more needs to be known about the charges and the evidence supporting them before anyone can finally judge whether the case was rushed forward by an over-ambitious prosecutor. For the moment, however, you might just as easily conclude that action was not too rushed, but too long delayed. The current charges -- which involve Mr. Donovan only as one among several indicted officers of his firm -- grow out of court-approved FBI surveillance activities back in January 1979. The 857 tapes covered, among much else, dealings between Mr. Donovan's firm, Schiavone Construction Co. and Jopel, a subcontractor run by a convicted racketeer, William Masselli.

The FBI has apparently been very reluctant to share the fruits of its investigations with local prosecutors. Its own investigation of Jopel, announced well before Mr. Donovan took office, has moved at a tortoise-like pace. The Bronx prosecutor's office did not become aware until last year that the FBI tapes contained evidence relevant to an unsolved 1978 murder with which the same grand jury has now charged Mr. Masselli. It then had to spend several months haggling with the FBI to get access to the tapes. Some charges covered in the indictments date back to September 1979. The five-year statute of limitations would apparently have put them beyond the reach of prosecutors if the indictment had been delayed any longer.

Whether or not the timing of the indictments was politically motivated, it is certainly unfortunate from Secretary Donovan's perspective. Having already endured, and survived, prolonged investigation by a special prosecutor, he is determined to hold on to his high office while he establishes his presumed innocence of the current charges. But by insisting that he be allowed to take leave without pay rather than resign, the secretary has clearly not done the president any favor.

Leaving a Cabinet office vacant for a possibly prolonged period should cause both political and administrative difficulties for a president. Perhaps in this administration -- which has never had any interest in the Labor Department or much faith in the things it might do -- the loss, at least in administrative terms, will not be great.