Chief Deputy School Supt. Charles Mitchell Jr. resigned today, after admitting that he invented the story that electronic bugs were found in the office and auto of School Supt. Ruth B. Love.

At a crowded news conference, Love apologized to Mayor Jane Byrne and the school board "for bringing this embarrassment to the city and to the Chicago schools."

Mitchell, who had held the position as Love's chief aide for a month after coming here, did not attend the news conference.

In a statement released by an aide, Mitchell said he "decided to state that wiretaps were found in order that this information would serve as a precautionary measure to discourage the possibility of future wiretaps."

Mitchell added that the superintendent did not know that the wiretap story was a hoax. Love said at the news conference that this was the case, but that she accepted responsibility for the situation.

In his statement, Mitchell wrote: "Hindsight tells me I was wrong and in my zeal to protect the superintendent and the confidentiality of her office, I should have used better judgment. I also realize that I put myself in an untenable position and therefore offer my resignation, effective immediately."

Mitchell said he was particularly sensitive to security considerations because he came to Chicago with Love from Oakland, Calif., where Love's predecessor was assassinated by members of the radical Symbionese Liberation Army.

"This incident serves to demonstrate the importance of candor and the need to resolve problems expeditiously and openly," Love said.

Mitchell's resignation came as FBI agents sought unsucessfully to locate the 43-year-old educator to obtain evidence that the alleged bugging had taken place. Mitchell, who was a school administrator in the Detroit area before working with Love in Oakland, had claimed that a private investigator from Detroit had discovered electronic eavesdropping devices in Love's car and office early in April, after being hired by Mitchell to make inspections. But law enforcement officers following up Mitchell's story could not locate any such investigator.

The first public disclosure of the claim of the findings of the bugs had been was made Saturday.

On Monday, Love told the board privately that wires from eavesdropping devices led from her office to City Hall, according to several board members and her director of communications, Doris A. Payne. However, after conferring Tuesday with Payne and Mitchell, Love said she didn't know where the wires led. Before dropping from sight, Mitchell said he didn't know where the bugs led and denied that he had told Love of a link to City Hall.