WASHINGTON — Supreme Court Justice William J. Brennan resigned Friday after a 33-year career as a leading voice of liberalism on the nation’s highest court.

Brennan, 84, said his “advancing age and medical condition” led to his decision to step down.

His departure gives President Bush his first chance to name a justice to the court, which has been deeply divided in recent years on such issues as a woman’s right to an abortion, affirmative action and separation of church and state. Brennan has been a firm advocate of all three.

Bush, a strong opponent of abortion, was traveling in Wyoming when Brennan’s decision was made public.

Brennan’s brethren praised his service.

Justice Thurgood Marshall said Brennan has been a “voice of caution and compassion in urging that this court not retreat from its constitutional mission to protect individuals’ rights of freedom and expression, guarantee that minorities be free from discrimination and to assure the rights of those accused of crimes.”

Sen. Edward M. Kennedy hailed Brennan — appointed by President Eisenhower in 1956 — as one of “the greatest justices the country has ever had.”

Last April, just days before his 84th birthday, Brennan said he had no intention of retiring unless his health required it.

In his letter to Bush, Brennan said: “strenuous demands of court work and its related duties required or expected of a justice appear at this time to be incompatible with my advancing age and medical condition.”

“I, therefore, retire effectively immediately as an associate justice of the Supreme Court of the United States.”

National Public Radio reported that Brennan suffered a fall and a small stroke recently and talked over his health with his wife before deciding to leave the court.

Brennan also suffered a small stroke in 1979 that left his right arm and hand partially paralyzed, and in 1978 underwent radiation treatments for a cancerous tumor in his throat.

“This was a very difficult decision after almost 34 years of service on the court,” Brennan said in a statement.

“It is my hope that the court during my years of service has built a legacy of interpretation of the Constitution and federal laws to make them responsive to the needs of the people whom they were intended to benefit and protect. This legacy can and will withstand the test of time.”

Brennan served under eight presidents. His departure is bound to cause a dramatic change in the liberal-conservative balance at the court.

For more than three decades, Brennan has been a leading exponent of liberalism and, by most accounts, a leading behind-the-scenes strategist in helping mold liberal rulings and in later years in preserving them on an increasingly conservative court.

Appointed to the court by President Dwight D. Eisenhower, he quickly found a home among the liberal majority led by Chief Justice Earl Warren.

Along with fellow liberal Justice Marshall, Brennan has maintained that the Constitution forbids the death penalty as cruel and unusual punishment.

He remains among four justices on the court who wholeheartedly support the court’s 1973 ruling that legalized abortion nationwide.

He also was the author of a landmark ruling that gave the news media broad protection against libel suits by public figures.