Frank M. Johnson Jr., 80, a federal judge whose decisions in civil rights and related fields gave substance to the Constitution's promise of equal protection of the law for all citizens and made him one of the most controversial, influential and admired jurists of the age, died of pneumonia July 23 at his home in Montgomery, Ala.

First as a U.S. district judge in Alabama and then as a member of the 11th U.S. Circuit Court of Appeals, Judge Johnson played a leading role in setting the nation's course on civil rights, access to public facilities, voting rights, school desegregation, employment discrimination and affirmative action.

He also made important rulings involving the rights of patients in state mental hospitals and the treatment of inmates in state prisons. By imposing federal mandates on such activities, previously regarded as being the exclusive responsibility of state governments, he helped redefine the relationship between the federal government and the states, a still-developing area of the law.

Although he was a man of the law rather than a reformer or a politician, many of his decisions had social and political consequences that have become touchstones of American life as the 20th century draws toward its close.

Among Judge Johnson's best-known cases was one in which Rosa Parks refused to give up her seat on a Montgomery, Ala., bus as required by local law, the act which started the modern civil rights movement. Judge Johnson ruled that the regulation in question violated the "due process and equal protection clauses" of the 14th Amendment to the Constitution. In doing so, he became the first judge to apply the principles laid down by the U.S. Supreme Court in Brown v. Board of Education, which outlawed segregated public education, to non-school issues.

In 1965, he issued an order that allowed the famous voting-rights march from Selma, Ala., to Montgomery to proceed. When civil rights demonstrators tried to cross the Edmund Pettus Bridge in Selma to begin their march, they were beaten by Alabama state troopers in an incident that became known as Bloody Sunday. Among the victims was John Lewis, now a Democratic congressman from Georgia. Unforgettable images of Lewis and others being clubbed to the ground were carried by newspapers and television stations across the world. The effect was to galvanize support for civil rights.

State officials, led by Gov. George C. Wallace, a strong segregationist, sought a court order prohibiting plans to continue the march to Montgomery, claiming it would lead to more violence. After a four-day hearing, Judge Johnson cleared the way for the marchers.

In his opinion, he said the events at the Pettus Bridge "involved nothing more than a peaceful effort on the part of Negro citizens to exercise a classic constitutional right: that is, the right to assemble peaceably and to petition one's government for the redress of grievances . . .

"It seems basic to our constitutional principles that the extent of the right to assemble, demonstrate and march peaceably along the highways and streets in an orderly manner should be commensurate with the enormity of the wrongs that are being protested and petitioned against. In this case, the wrongs are enormous. The extent of the right to demonstrate against these wrongs should be determined accordingly."

One result of the incident was that President Lyndon B. Johnson addressed the nation and announced his intention to introduce what became the Voting Rights Act of 1965.

In other cases, Judge Johnson struck down an Alabama law that barred blacks and women from serving on juries; signed an order integrating the University of Alabama; took part in the case that led eventually to the Supreme Court's "one man, one vote" rule; ruled that court-appointed defense attorneys must be paid from public funds; desegregated the Alabama state police; and took part, either as an individual judge or as a member of a panel, in decisions that desegregated parks, restaurants, transportation facilities and schools.

In 1978, he ruled that Alabama State University had discriminated against whites in its hiring practices. It was the first time such a ruling had been handed down against a black institution.

Judge Johnson had notable clashes with Wallace, who was a classmate of his at the University of Alabama. In a 1959 voting rights case, he ordered Wallace, then a state judge, to turn over voting registration records to the U.S. Civil Rights Commission. Wallace complied by giving the records to a local grand jury, which forwarded them to the federal agency. When Johnson said Wallace had cooperated with a federal court order, Wallace said that the judge was an "integrating, carpetbagging, scalawagging, bald-faced liar."

When Judge Johnson ruled that state prisoners were entitled to adequate food and medical treatment, Wallace, then governor, accused him of trying to turn state prisons into hotels. Johnson replied, "The elimination of conditions that will permit maggots in a patient's wounds for over a month before his death does not constitute the creation of a hotel atmosphere."

Judge Johnson was a Republican when the South was almost entirely Democratic, a World War II veteran who was wounded in action and a former federal prosecutor. When he was named to the bench in 1955, he became, at 37, the youngest federal judge in the country. Until a federal appeals court ordered him to do otherwise, he presided over his court without wearing a robe or using a gavel--these traditional appurtenances of authority, he explained, were unnecessary to maintain order.

Although he had a reputation for judicial innovation, Judge Johnson described himself as a "hillbilly conservative." To the Rev. Dr. Martin Luther King Jr., the martyred civil rights leader, he was the person who gave "true meaning to the word justice." To many conservatives, his decisions were anathema. The Ku Klux Klan called him "the most hated man in Alabama."

Through the years, he received innumerable threats. From 1961 to 1975, he was under round-the-clock guard by federal marshals. On one occasion, a cross was burned on his lawn. On another, the carport of his mother's house was bombed by someone who thought it was his residence. No one was injured.

It was frequently reported that he was socially ostracized. He dismissed this as unimportant, telling an interviewer that it might have "kept me awake three or four minutes" at one time.

With the passage of years, the views fellow Alabamians had of him changed, and in 1992, the federal courthouse in Montgomery was named in his honor.

In his rulings, Judge Johnson established himself as a leading and unapologetic judicial activist. "The doctrine of neutral principles robs the Constitution of its vitality," he once said. "It freezes constitutional thinking in the interest of theoretical purity. The framers were pragmatic men, and the Constitution is a practical blueprint. Its genius lies in its generality. Perfect logical consistency has always given way to practical distinction, as well it should."

In an address at the Boston University law school in 1979, he warned against both inconsistency and "unprincipled distinctions" in interpreting the Constitution.

"Religious differences, race differences, sex differences, age differences and political differences are not the same," he said. "It is no mark of intellectual soundness to treat them as if they were. Moreover, if the life of the law has been experience, then the law should be realistic enough to treat certain issues as special: as racism is special in American history. A judiciary that cannot declare that is on little value."

He was quick to answer criticism that he and other judges were exceeding their authority, usurping the functions of legislatures and imposing their own views on events rather than applying established legal principles.

"It is one thing for a judge to adopt a theory of political morality because it is his own," he said in an interview. "It is another for him to exercise his judgment about what the political morality implied by the Constitution is. If federal judges appear more activist, it is not because they have appointed themselves roving commissioners of good. Rather it is because new procedures have opened the doors of the federal courthouse to new interests."

In a speech to the American Bar Association when he received its Thurgood Marshall Award in 1993, he said, "It is the obligation of every judge to see that justice is done within the framework of the law. I have attempted to fulfill that obligation by applying the rule of law to the facts before me. . . . I am confident that my faithful adherence to the rule of law had yielded true justice."

Frank Minis Johnson Jr. was born in Haleyville, a small town in northwestern Alabama, on Oct. 30, 1918. His father was a farmer, a high school teacher and the local probate judge and postmaster. His mother, Alabama Long Johnson, was a teacher.

Republican sentiment was strong in that part of the state. When the Civil War broke out, Winston County, where Haleyville is located, considered seceding from Alabama, and more men from the county served in the Union Army than in the Confederate Army. The Johnson family had soldiers on both sides. When the future judge was growing up, his father was the only Republican member of the Alabama legislature.

Frank M. Johnson Jr. attended Birmingham-Southern College on a football scholarship. He later transferred to Massey Business College in Birmingham, Ala. As a junior he enrolled in the prelaw program at the University of Alabama. He then graduated from the University of Alabama's law school at the top of his class in 1943.

He enlisted in the Army, but soon became a commissioned officer. He took part in the Normandy invasion on June 6, 1944, and was wounded five days later. When he recovered, he was stationed in England as a lawyer with the Judge Advocate General's Corps. After the war, he practiced law in Jasper, Ala.

In the 1952 presidential campaign, Judge Johnson headed Alabama Veterans for Dwight D. Eisenhower. In 1953, Eisenhower named him U.S. attorney for the northern district of Alabama. He remained in that job until he became a judge.

In 1977, President Jimmy Carter nominated Judge Johnson to be director of the FBI, but the judge withdrew his name for health reasons. In 1979, Carter elevated him to the federal appeals court.

Judge Johnson's survivors include his wife, the former Ruth Jenkins, whom he married in 1938, of Montgomery. A son, James Curtis Johnson, died in 1975.