William Hubbs Rehnquist, the 16th chief justice of the United States, died last night at his home in Arlington. He was 80.

Rehnquist, who had been suffering from thyroid cancer since last October, had managed to lead the Supreme Court through its last term, which ended in June. But he went through "a precipitous decline in his health in the last couple of days," court spokeswoman Kathy Arberg said.

Rehnquist's death comes as the Senate is preparing for hearings on President Bush's nomination of John G. Roberts Jr. to replace Sandra Day O'Connor as an associate justice. Those hearings are set to begin on Tuesday. O'Connor, 75, announced her retirement on July 1, effective upon the confirmation of a successor.

Bush must now name a replacement for Rehnquist, and the process of selecting and confirming a new justice will probably last past the first day of the court's new term, Oct. 3. That means that even if Roberts is swiftly confirmed, the Supreme Court will be operating with only eight members for an indefinite period.

Tie votes on the high court result in the automatic affirmance of a lower court's ruling, but they do not establish a legal precedent.

A conservative stalwart appointed as associate justice by President Richard M. Nixon in 1972, Rehnquist was elevated to chief justice in 1986 by President Ronald Reagan. His 33-year tenure on the court was one of the longest and most influential in the institution's history, as he spearheaded a rightward move at the court -- first as a lone dissenter, then later as the leader of a five-justice conservative majority.

Already preoccupied with the recovery effort after Hurricane Katrina and the Roberts nomination battle, Bush must now focus on a successor for Rehnquist. But Rehnquist's illness has prepared the White House for the possibility that he would be leaving the court, so the element of surprise should be less than it was in the case of O'Connor's retirement.

Among those who have been mentioned as possible choices are Alberto R. Gonzales, the attorney general, and federal appeals court judges J. Michael Luttig and J. Harvie Wilkinson, both of the U.S. Court of Appeals for the 4th Circuit, based in Richmond.

"The president and Mrs. Bush are deeply saddened at the passing of Chief Justice Rehnquist," the White House said in a statement. "His family is in their thoughts and prayers." An aide said Bush was informed of Rehnquist's death shortly before 11 p.m. and added that the president will make a statement to reporters about the chief justice this morning after attending church services.

Rehnquist leaves a towering legacy. As a young lawyer in Phoenix in 1957, he declared a personal war of sorts against the Supreme Court, then headed by Chief Justice Earl Warren. Rehnquist gave a speech criticizing Warren and Justice Hugo Black as "left-wing philosophers." He published a magazine article blaming the Warren court's liberal drift on the "political cast" of the justices' law clerks.

Rehnquist's effort to roll back the modern liberal tide would take him to Arizona Republican Sen. Barry Goldwater's ill-fated 1964 presidential campaign, to the Nixon administration's Justice Department and eventually, in 1972, to the court itself.

Now, after 33 years there -- the last 18-plus of them as chief justice -- Rehnquist could claim to have fought Warren to a draw.

Key Warren Court rulings -- among them the ban on school prayer and the Miranda case guaranteeing a suspect's "right to remain silent" -- have survived. And the post-Warren Roe v. Wade decision, the abortion rights ruling that Rehnquist tried to overturn, also seems entrenched, for now.

Yet the Rehnquist Court has strengthened the legal position of the police, paved the way for swifter executions, defined constitutional limits on federal power and permitted indirect government funding of religious schools.

Though Rehnquist and his fellow conservative justices often acted in the name of judicial restraint, it is perhaps more accurate to say that they showed an active court could serve conservative policy ends as well as liberal ones.

During Rehnquist's tenure, the Supreme Court has arguably expanded its role in American life, frequently striking down laws passed by Congress, subjecting the president to independent-counsel investigations and private lawsuits and, in 2000, settling a presidential election.

Though the full scope of the Rehnquist counterrevolution is still much debated, legal scholars already rank him among the court's great chief justices.

"When the history of the Supreme Court in the 20th century is written, there will be two great chief justices: Earl Warren and William Rehnquist," said Mark Tushnet, a professor at the Georgetown University Law Center. "Both presided over courts that changed the law in a very dramatic way."

Still, as his tenure concluded, there was a sense at the court that Rehnquist's most influential days were already behind him. In recent terms, he suffered defeats on issues he cares deeply about, such as affirmative action in university admissions, which the court sustained, and state sovereignty and individual property rights, which it curbed. He cast a vote but expressed no written opinion in the court's historic decision last year granting federal court access to prisoners at Guantanamo Bay, Cuba.

His impact has been blunted by his inability to win over the court's vital center, as represented by fellow Republican appointees Sandra Day O'Connor and Anthony M. Kennedy.

Yet, as Tushnet noted, the remarkable fact is that Rehnquist even came close.

"When he started, the law was tilted in a liberal direction," Tushnet added. "Now it's not really tilted in a conservative direction, but it's more of a level playing field."

Rehnquist was born on Oct. 1, 1924, in Milwaukee and grew up in the suburb of Shorewood, Wis., where he attended the local public schools. When a grade-school teacher asked him what he was going to do when he grew up, the loyal son of anti-New Deal parents did not hesitate: "I'm going to change the government," he said.

He started his college education at Kenyon College in Ohio in 1942 but was drafted in March 1943. He worked as a weather forecaster for the U.S. Army Air Forces at bases in the southwestern United States and North Africa. He would later say that his time in these warm, dry climates persuaded him to settle in Arizona as a young adult.

After the war, he attended Stanford University and Stanford Law School, where he graduated first in his class in 1952. For 18 months after that, he served as a law clerk to Justice Robert H. Jackson on the Supreme Court.

Rehnquist met his future wife, Natalie "Nan" Cornell, at Stanford. They married in 1953; she worked at the CIA while he clerked for Jackson. Her death from ovarian cancer in 1991 was a devastating blow to Rehnquist.

As a young man, Rehnquist seemed to relish waging his own war of ideas against liberalism. Working for Jackson, he fired off tart memos to his boss, including such remarks as, "I take a dim view of this pathological search for discrimination" against blacks. He suggested that "drawing and quartering" would be a more appropriate punishment than the electric chair for Julius and Ethel Rosenberg, convicted of nuclear espionage for the Soviet Union.

As the court weighed Brown v. Board of Education, the landmark case that banned segregation in the public schools, Rehnquist wrote a memo defending Plessy v. Ferguson, the 1896 ruling that had established the now-discredited doctrine of "separate but equal." That decision, Rehnquist wrote, "was right and should be reaffirmed."

When challenged over the memo during his 1971 confirmation hearings, Rehnquist said it was intended to reflect Jackson's views, not his, and that he "unequivocally" supported Brown. Historians have taken a skeptical view of that explanation.

In Arizona, Rehnquist became active in the Republican Party. He served as general counsel of the state Republican committee and wrote speeches for Goldwater in his losing 1964presidential campaign.

Also in 1964, Rehnquist was one of three people to testify against a proposed ordinance to ban discrimination in public accommodations in Phoenix. When it passed, he wrote a letter to the editor of the local paper saying that "it is, I believe, impossible to justify the sacrifice of even a portion of our historic individual liberty for a purpose such as this."

He also repudiated that view during his 1971 confirmation.

By the time Nixon was elected president, in 1968, Rehnquist had made a good impression on a fellow Arizonan, Richard Kleindienst, who was heading east to join the Justice Department. Kleindienst helped Rehnquist land a job as assistant attorney general for legal counsel, a position in which Rehnquist advised the administration on constitutional law. He wrote a memorandum proposing a commission to draft constitutional amendments overturning the Warren Court's rulings on criminal law.

In 1969, as antiwar demonstrations raged in the streets, Rehnquist warned a Kiwanis Club in Newark of "the danger posed by the new barbarians," adding that "if force or the threat of force is required in order to enforce the law, we must not shirk from its employment."

He was serving at the Justice Department in October 1971 when Nixon selected him to fill a vacancy left by the retirement of Justice John Marshall Harlan. Rehnquist, then 47, was reportedly stunned by the choice, which was indeed somewhat serendipitous: Nixon turned to him after his judge-picking team, of which Rehnquist was a member, failed to produce a satisfactory choice.

Nixon was looking for a cerebral conservative, and Rehnquist did not disappoint.

He soon became known as the "Lone Ranger" because he was so often the sole dissenter on the nine-member court.

Rehnquist opposed the court's short-lived 1972 opinion overturning state death penalty laws. He was one of only two justices to vote against Roe v. Wade in 1973. He opposed affirmative action in higher education. Alone among the justices, Rehnquist said in 1983 that Bob Jones University had a legal right to exclude black students from its campus.

Through it all, Rehnquist was motivated by a basic sympathy for law enforcement and the public order it protected, and a certain disdain for the notion that the Supreme Court existed to establish the fairness in society that some might find lacking. That was a job for the legislature, he insisted.

"[F]or the courts to come along and say in addition to that, you know, 'We just don't like what happened here. We think it's, quote, unjust, close quote' is giving them a rather subjective mandate that I think many people . . . if they fully understood it, would find troubling," he told an interviewer on Fox News in 2001.

He also held the view that the Warren Court had gone beyond what the framers of the post-Civil War 14th Amendment had intended in guaranteeing "equal protection of the laws" by state governments. Rehnquist felt that, in fact, the amendment was meant to proscribe a narrow range of discriminatory conduct and that only the Supreme Court, not Congress, had the power to say what that conduct would be.

He was particularly offended by what he saw as the excessive use of petitions for habeas corpus by criminal defendants to challenge their state convictions and sentences in federal court. Those constitutional challenges affronted state sovereignty, Rehnquist believed, and excessively delayed executions.

Inside the court, Rehnquist was generally well-liked, despite his disagreements with colleagues about the law. Gangling and affable, he lacked pomposity and enjoyed practical jokes -- probably the most famous of which occurred on April Fool's Day 1986, during the tenure of Chief Justice Warren E. Burger.

Rehnquist had a life-size photo cutout of Burger made and sent a photographer out to the front of the court with a sign that said: "Have your picture taken with the chief justice. $1." He then arranged to drive by with Burger, enjoying a hearty laugh at Burger's reaction.

When Reagan named him to replace Burger as chief justice, in 1986, Rehnquist brought a new tone to the job.

He was a stickler for decorum and punctuality in the courtroom and occasionally erupted at wayward lawyers. Yet behind the closed doors of the justices' weekly conferences, Rehnquist was appreciated for his evenhandedness and calm -- which justices found a welcome contrast to the imperious Burger.

On Jan. 7, 2002, the 30th anniversary of Rehnquist's swearing-in, Justice John Paul Stevens, who rarely agreed with him on the issues, read a statement from the bench praising the chief justice for "the efficiency, good humor and absolute impartiality that you have consistently displayed when presiding at our Conferences."

Rehnquist believed that the court should reserve its time and effort for cases of national importance that absolutely require its attention; the number of cases decided by the court after briefing and oral argument declined on his watch from 152 in 1986-1987, his first term as chief justice, to 76 in the 2004-2005 term.

With the confirmation of Justice Clarence Thomas in 1991, Rehnquist had the five usually conservative votes he needed to put his views of the law into effect. Habeas corpus was further reined in. Affirmative action was subjected to the same degree of constitutional scrutiny as discrimination against minorities.

The Federalist Five, as Rehnquist, O'Connor, Antonin Scalia, Kennedy and Thomas came to be known, issued a series of rulings that struck down efforts by Congress to subject state governments to laws protecting women against domestic violence, banning guns near school property and prohibiting discrimination against disabled workers.

To critics, this was an effort to roll back the primacy of the national government that had been established by the Union victory in the Civil War. To supporters, the court was restoring an appropriate balance of power. But there was no question who the driving force behind the cases was.

"You can't identify anyone who's had more to do with the revival of federalism than Bill Rehnquist," said John C. Jeffries Jr., dean of the University of Virginia Law School. "That means not only limits on federal legislative power, but also that state legislative power ought to be respected."

The same majority voted in 2002 to permit a school tuition voucher program in Cleveland that funneled taxpayer dollars to parochial schools. That opinion, by Rehnquist, embodied an argument that the chief justice had first expressed in a dissenting opinion in 1973.

Rehnquist's support for state autonomy was so strong that it could trump his distaste for things countercultural. But this year, when he voted to block a federal override of California's law permitting possession of homegrown medical marijuana, he found himself in the minority, abandoned not only by Kennedy but also by Scalia.

With the marijuana case, the federalism drive at the court appears to have stalled out, just as Rehnquist had earlier been thwarted on other key issues when O'Connor, Kennedy or both were not quite prepared to follow his philosophy to its more politically risky conclusions.

The two justices defected to the liberal side in a key 1992 case, with the result that Roe v. Wade was upheld and its status as a constitutional precedent strengthened. In 2003, O'Connor provided the fifth vote to uphold affirmative action in university admissions, with Rehnquist writing a biting dissent.

Generally, though, as chief justice, Rehnquist made less frequent use of the luxury of principled disagreement with his colleagues than he had as an associate. When it was clear that most justices opposed one of his long-held positions, he would sometimes join the majority and assign the opinion-writing to himself -- a prerogative of the chief justice -- in order to limit what he saw as the damage.

Thus, when the court voted 7 to 2 to uphold the Miranda decision in 2000, Rehnquist wrote the opinion, a rather grudging acknowledgment of Miranda's status as unchangeable precedent; Scalia and Thomas dissented.

In 2003, O'Connor declined to invalidate provisions of the Family and Medical Leave Act that subjected the states to private lawsuits for alleged failures to treat their male and female workers equally in granting time off.

Rehnquist assigned the case to himself, supplying a bare-bones opinion that reiterated many of the court's past federalist principles even as it explained why they did not apply in the context of a law against gender discrimination in employment. The alternative was to dissent and leave the majority opinion to the liberal Stevens.

"He became a bit more muted and focused" as chief justice, said Dennis J. Hutchinson, a professor of law and history at the University of Chicago. "He grew into a very savvy operator."

Though still ideologically unreconstructed in almost every respect, as Chief Justice Rehnquist came to acknowledge, and appreciate, the limits that the law itself places on any individual's ability to alter the court's direction.

Asked by Fox News reporter James Rosen in 2001 whether his esteem for Warren had grown, Rehnquist said that it "probably did, partly out of respect for stare decisis. That is the principle that once an issue has been decided, it should stay decided. You can't constantly be relitigating things without doing a lot more damage than just leaving them in place."

Rehnquist is survived by his three children, James Rehnquist of Boston, Nancy Spears of Middleburg, Vt., and Janet Rehnquist of Arlington, who were at his side when he died last night, Arberg said. He had nine grandchildren.

Chief Justice of the United States William H. Rehnquist sits for a formal photo in 2003. In 1971, William H. Rehnquist, President Nixon's choice for the Supreme Court, turns to Sen. Barry Goldwater, R-Ariz., left.In 1986, President Reagan introduces the new chief justice, William H. Rehnquist, center, as retiring Chief Justice Warren Burger smiles.After swearing in President Bush in January 2005, Chief Justice William H. Rehnquist departs, drawing a salute from a four-star Air Force general.