The Supreme Court (search) returns Monday with an ailing leader, pressure to rule quickly on the constitutionality of federal prison sentences and a slew of contentious issues to decide, from medical marijuana to Ten Commandment (search) displays.

The most immediate concern is the health of Chief Justice William H. Rehnquist (search), who was diagnosed with thyroid cancer in October. He has been working part time at the court for more than two weeks but still is too ill to return to the bench.

At 80, Rehnquist already was considered a top retirement prospect on a court that has had no turnover in a decade, a record. But justices try to time their departure's for the court's summer recess, to avoid 4-4 ties in cases.

Rehnquist's absence has yet to produce any tie votes. Even though he missed all the arguments in November and December, he has reviewed the cases and could vote if needed.

"I suspect no matter what his health, he'll do whatever he can to hang in there," said Stephen McAllister, law school dean at the University of Kansas and a former Supreme Court clerk. "There is nothing that frustrates them more than an eight-person court."

Besides Rehnquist, Justices John Paul Stevens, 84, and Sandra Day O'Connor, 74, are considered possibilities to leave this year.

McAllister predicted court vacancies "will be the big story of 2005."

But there will be others.

Justices could rule as early as this week on whether the longtime system for sentencing federal defendants should be thrown out because it lets judges, rather than juries, decide factors that add years to prison time. Many judges have delayed sentencings while awaiting the high court's decision.

Other major cases involve whether states can execute juvenile killers, whether the federal government can prosecute people who use marijuana medicinally, and whether states can bar interstate wine sales over the Internet.

Some other big issues are still to be argued — or are awaiting an announcement on whether the justices will hear them.

Two February cases will be closely watched by local governments and land rights groups. They involve the government's power to take people's land or put limits on its use.

In early March, large crowds are expected when justices take up two cases that question the constitutionality of government displays of the Ten Commandments. The last major religion case was last year's challenge to the words "under God" in the Pledge of Allegiance (search). Justices settled the case without ruling on the merits.

March also brings a case that asks how U.S. authorities should deal with foreign nationals facing charges that could result in execution. In addition, there is an Internet dispute that questions whether file-sharing services may be held responsible when their customers illegally swap songs and movies online.

Justices have a chance to add some controversial issues to their April calendar: Oregon's assisted suicide law, a Florida law that kept a severely brain-damaged woman alive over her husband's objections, a Florida law that bars gays from adopting, and an appeal questioning the Bush administration's strategy to hold military trials for terror suspects in Guantanamo Bay, Cuba.

"I don't think there's going to be any shortage of headlines," said Erwin Chemerinsky, a Duke University law professor. He will argue two cases this spring — on behalf of a man challenging a Ten Commandments display in Texas and a disgruntled former client of defense lawyer Johnnie Cochran.

Also awaited is a White House announcement on a permanent lawyer to represent the administration in cases at the high court. Solicitor General Theodore Olson left last summer. His deputy, Paul Clement, has held the job on an interim basis.