DETROIT — Mayor Kwame Kilpatrick was charged with perjury and other offenses yesterday — and got a stern lecture about the importance of telling the truth — after a trove of raunchy text messages contradicted his sworn denials of an affair with his chief aide.

The 37-year-old “Hip-Hop Mayor” who brought youth and vitality to the job in this struggling city of 900,000 could get up to 15 years in prison for perjury alone and would be automatically expelled from office if convicted.

Ignoring mounting demands that he step down, Mr. Kilpatrick said: “I look forward to complete exoneration once all the facts have been brought forth. I will remain focused on moving this city forward.” The Wayne County Prosecutor, Kym Worthy, brought charges of perjury, conspiracy, obstruction of justice, and misconduct against the popular but polarizing mayor.

In announcing the charges, she delivered something of a civics lesson on the importance of telling the truth under oath.

“Some have suggested that the issues in this case are personal or private,” Ms. Worthy, who along with the mayor is a Democrat, said. “Our investigation has clearly shown that public dollars were used, people’s lives were ruined, the justice system severely mocked, and the public trust trampled on.”

She added: “This case is about as far from being a private matter as one can get.”

Mr. Kilpatrick’s former chief of staff, Christine Beatty, 37, who also denied under oath that she and Mr. Kilpatrick had an intimate relationship in 2002 and 2003, was charged with many of the same offenses. A call to her lawyer was not immediately returned.