Detroit Mayor Kwame Kilpatrick and his former chief of staff, Christine Beatty, pleaded not guilty today to charges of lying under oath about an affair and using taxpayer money in an attempt to cover it up.

The pair face charges of perjury, conspiracy, obstruction of justice and misconduct in office. They were released on $75,000 bail each, and preliminary examination has been set for June 9.

If convicted of all charges, Kilpatrick could face up to 90 years in jail.

The mayor has vowed to fight the civil felony charges, which grew out of an $8.4-million settlement of a lawsuit against him by police officials and the leaking of steamy romantic text messages he exchanged with Beatty.

In a brief news conference Monday, Kilpatrick had dismissed the case against him as "a very flawed process from the beginning." But the seriousness of the charges is daunting.

The indictment is the latest development threatening to derail Kilpatrick's meteoric rise. The youthful political figure gained fame as "the hip-hop mayor," both for his election at age 31 in 2001 and his penchant for the high life. Kilpatrick, who is married and has three children, has been dogged by allegations of a party at the mayor's mansion that featured appearances by strippers and recent revelations about his affair with Beatty.

Wayne County prosecutor Kym Worthy accused the mayor of lying under oath during a "public whistle-blower" trial last fall and trying to obstruct justice by attempting to hide his extramarital relationship with Beatty, who was charged with seven felony counts.

"Even children understand that lying is wrong," Worthy said Monday, adding that "lying cannot be tolerated even if a judge and jury sees through it."

Worthy's filing had been expected for weeks. And as her investigators wrapped up their work last week, the Detroit City Council voted 7 to 1 to demand Kilpatrick's resignation, heightening the animosity between Detroit's political community and Kilpatrick's embattled inner circle.

One council veteran worried aloud Monday that the city's business could be hampered by the prospect of a long trial.

"We have a constitutional crisis in this city," said City Councilwoman Sheila Cockrel, who questioned the mayor's insistence that he would move ahead with plans for a $300-million economic stimulus package. "There are basic items of city governance that need clear mayoral focus. I don't see how he can do that."

Kilpatrick's lawyer, defense attorney and former federal prosecutor Daniel Webb, criticized the charges as "a weak prosecution case" and said he had advised his client not to resign.

"I don't think he's going to be distracted," Webb said in a telephone interview. "He can govern the city of Detroit. For him to cave in and resign would be to let politics trump his right to a jury trial."

Kilpatrick also tried to defuse public concerns about his legal defense and political effectiveness by turning to a Washington-based public relations group that set up interviews with Webb.

Revelations of the sexually explicit cellphone text messages between Kilpatrick and Beatty exposed their relationship, made the 37-year-old mayor the target of public ridicule and indicated that he may have intimidated police officials in order to contain the damage from his affair.

Kilpatrick's troubles stem from lawsuits filed against the city by several members of his police security detail, who complained they were punished for investigating allegations of misconduct by the mayor and his bodyguards.

Both the mayor and Beatty testified during legal proceedings last fall that they did not have a relationship, but after the city approved an $8.4-million settlement with the police officials, the Detroit Free Press in January released racy snippets from more than 14,000 text messages sent to and from Beatty's city-provided pager in 2002 and 2003.

Despite insisting during the trial in August that he did not have an affair with Beatty, Kilpatrick had told her in a 2002 text message, "I'm madly in love with you."

Worthy was quick to insist Monday that her case was not "focused on lying about sex." The investigation had expanded, she said, to grapple with the firing of one Detroit police officer and allegations of pressure against several others.

"Public dollars were used, people's lives were ruined, the justice system was severely mocked and the public trust trampled on," she said.

Worthy also angrily accused city officials of "machinations" that slowed her investigation "at every bend and turn."

She did not detail the hurdles that her investigators faced, but Sheila Cockrel and her stepson, City Council President Kenneth Cockrel Jr., have questioned the actions of city lawyers and officials who failed to cooperate with investigators. The council is taking steps to order city officials to cooperate with its investigation.

Sheila Cockrel said that the council president was "signing subpoenas for documents and records that go to the very heart of the role the city law department and other city personnel have played in keeping this confidential [settlement] agreement away from council members."

stephen.braun@latimes.com

Times staff writer Sarah D. Wire contributed to this report.