The Reagan administration's top choice for a seat on the Nuclear Regulatory Commission has been found by the Wisconsin State Attorney General to have violated state law, but will not be prosecuted.

Willie J. Nunnery, a member of the Wisconsin Public Service Commission, worked simultaneously last summer as a part-time hearing examiner for the District of Columbia Public Service Commission. Under Wisconsin law, PSC members are forbidden from holding any other paying positions.

The decision was made by Attorney General Bronson La Follette who recommended that Nunnery be prosecuted by the Dane County District Attorney in Madison, the state capital.

However, District Attorney James E. Doyle Jr. determined that although he agreed with the attorney general that Nunnery "violated Wisconsin statutes," his "conduct does not constitute a prosecutable offense." Breaking this law is not a criminal or civil offense, Doyle said.

Nunnery, 33, is a Republican, both a lawyer and an engineer and has served on the Wisconsin PSC since April 1980, for which he is paid $46,700 a year. As a part-time hearing examiner for the District PSC, he received more than $7,000 for work done in 1981.

Nunnery said that because of his engineering education, the D.C. PSC invited him to sit as a hearing examiner on "a particularly technical case" after he met some members of the District panel during a training program at Michigan State University in July 1980. Unlike other state commissions, the D.C. PSC does not employ full-time hearing examiners.

Nunnery's name has been circulated by White House aides on Capitol Hill as a likely nominee to replace Nuclear Regulatory Commission member Peter Bradford, who is scheduled to leave shortly to join the cabinet of the governor of Maine.

"I'm sorry about what happened and I hope it will not be the overriding factor in determinimng whether I will be nominated," Nunnery said.

Wisconsin State Sen. Joseph Strohl, who sought prosecution, said FBI agents have been checking Nunnery's background in preparation for his nomination to the NRC. Strohl, a Democrat, described Nunnery as "pronuclear power, proindustry rather than proconsumer . . . ."

According to Strohl, the controversy over Nunnery, who is black, had become a sensitive issue in the state, evoking allegations from blacks that efforts to prosecute Nunnery were racially motivated.