Penobscot County’s chief prosecutor may decide as soon as Friday whether to press charges regarding the appearance of two sheriff’s deputies in a re-election campaign advertisement for Gov. John R. McKernan.

District Attorney R. Christopher Almy said he received a formal complaint Thursday from sheriff’s candidate Timothy Richardson, who brought the commercial to Almy’s attention Tuesday.

Richardson maintains that Sgt. Larry Merrithew and Deputy Joel Peters appear illegally in the spot, in which McKernan claims he has been tougher in the drug war than has his Democratic opponent and predecessor in the office, Rep. Joseph Brennan. Some claim, however, that the legality of law-enforcement officers participating in political campaigns is open to interpretation.

Furthermore, the officers have said they thought they were participating simply in a public-service announcement about drug eradication rather than in a paid political spot.

Sheriff Edward J. Reynolds is accepting responsibility for the misunderstanding, saying that he, too, thought the final product was to be a public-service announcement. The officers’ participation was arranged through him.

“I just naturally assumed that (the initial contact) was from the Blaine House and not the campaign,” Reynolds said Thursday night.

Brennan has called for McKernan to pull the spot, partly because of the officers’ involvement and partly because he claims it misrepresents Brennan’s record on drugs.

Merrithew’s and Peters’ appearance in the ad also could constitute a violation of a county policy. Whether county officials will seek the same recourse remains to be seen.

Almy said Tuesday he would not launch his own investigation, but would pursue it only if his office received a formal request. In Richardson’s letter to him, which bore Wednesday’s date, the former sheriff contended that “Sheriff Edward Reynolds and the two officers are in direct violation” of a state statute governing solicitations by law-enforcement officers.