CHICAGO (AP) _ The newly appointed director of the city's Board of Ethics resigned Thursday after it was disclosed he had been named in a lawsuit for alleged violations of Louisiana campaign financing regulations.

Gary M. O'Neill, who served about a month as executive director of the Chicago Board of Ethics, was accused of violating Louisiana regulations while helping that state's Commissioner of Insurance Doug Green finance his successful 1987 election campaign.

In his resignation letter, O'Neill said he was quitting his job as head of the agency that enforces the city's ethics and financial disclosure laws ''because of my failure to disclose the fact that I was named in a civil complaint filed by the Louisiana Ethics Commission.''

''At no time has there been any finding of civil or criminal wrongdoing,'' his letter said.

O'Neill said he did not want his failure to discuss the matter when he was being interviewed for the job ''to reflect adversely on the Board or the work to be done.''

After submitting his resignation, O'Neill said it is ''unfortunate that people who aspire to public office have things happen in their lives that do come back to be a cloud over their head.''

Johnnie DeWilde, the ethics board's current deputy director, was appointed acting executive director effective immediately, the board announced.

O'Neill resigned one day after The Morning Advocate, a Baton Rouge, La., newspaper revealed that he had been named as a defendant in a lawsuit by the Louisiana Board of Ethics for Elected Officials.

The lawsuit accuses Green of attempting to conceal the true source of $2.2 million in contributions to Green's 1987 campaign.

The lawsuit said the campaign funds went from O'Neill and others to a company controlled by the head of a now-defunct insurance agency. The insurance agency, Champion Insurance Co., was regulated by Green's office.

The state's lawsuit was thrown out of a state district court in Baton Rouge last year when the ethics board's enforcement provisions were declared unconstitutional by a state judge. A rehearing of the issue is pending before the Louisiana Supreme Court.

O'Neill, 38, had a successful law practice and was active in Louisiana politics. He said he has been traveling extensively since he left Baton Rouge on May 1, and did not keep in contact with his law practice or state affairs.

The Morning Advocate said he dropped out of sight last spring shortly before his law firm's chief client, Champion, was placed in court-ordered liquidation.

The disclosure about the lawsuit against O'Neill surprised Chicago officials.

''If we had known about the allegations against Mr. O'Neill, we would not have hired him as executive director,'' Albert Hofeld, the ethics board's chairman, said Thursday.

''It's not that we think he's done anything wrong, but it places a cloud over the ethics board.''

O'Neill said he did not mention the Louisiana ethics case during his interview for the Chicago job because he considered the matter concluded.

''I didn't try to keep any information from them at all,'' he said.