Rosa Parks, a black seamstress whose refusal to relinquish her seat to a white man on a city bus in Montgomery, Ala., almost 50 years ago grew into a mythic event that helped touch off the civil rights movement of the 1950's and 1960's, died yesterday in Detroit. She was 92 years old.

Her death was confirmed by Dennis W. Archer, the former mayor of Detroit.

For her act of defiance, Mrs. Parks was arrested, convicted of violating the segregation laws and fined $10. In response, blacks in Montgomery boycotted the buses for nearly 13 months while mounting a successful Supreme Court challenge to the Jim Crow law that enforced their second-class status on the public bus system.

The events that began on that bus in the winter of 1955 captivated the nation and transformed a 26-year-old preacher named Martin Luther King Jr. into a major civil rights leader. It was Dr. King, the new pastor of the Dexter Avenue Baptist Church in Montgomery, who was drafted to head the Montgomery Improvement Association, the organization formed to direct the nascent civil rights struggle.

"Mrs. Parks's arrest was the precipitating factor rather than the cause of the protest," Dr. King wrote in his 1958 book, "Stride Toward Freedom. "The cause lay deep in the record of similar injustices."

Her act of civil disobedience, what seems a simple gesture of defiance so many years later, was in fact a dangerous, even reckless move in 1950's Alabama. In refusing to move, she risked legal sanction and perhaps even physical harm, but she also set into motion something far beyond the control of the city authorities. Mrs. Parks clarified for public consumption far beyond Montgomery the cruelty and humiliation inherent in the laws and customs of segregation.