Under the rules rejected by U.S. District Judge Paul A. Crotty, companies that own fuel-saving cabs would have been allowed to charge drivers slightly higher rental rates; companies with gas-hungry vehicles would see their rates decrease over a two-year period.

In October, Crotty rejected for the same reason other rules the city had devised to try to force the fleet of yellow cabs to go green by 2012. Those rules would have required new cabs to be fuel efficient.

The judge praised the city's intent but said efforts to encourage the purchase of hybrid vehicles must be careful not to interfere with Congress' exclusive jurisdiction over laws related to mileage or emission standards.

"The court's purpose is not to interfere with government officials taking actions in the public interest," he wrote. "Increasing the number of hybrid taxicabs is an appropriate and important governmental priority."

The judge noted there were no legal challenges to decisions by the city to issue new taxi medallions only to hybrid vehicles or to allow hybrid cabs to stay in service longer.

Michael A. Cardozo, head of the city's law department, said the city was disappointed.

"We do not believe that Congress intended to prohibit local governments from implementing incentive programs ... that encourage the purchase of environmentally friendly taxis. We are exploring our legal options," he said in a statement.

The court, with only one justice in dissent, avoided the major constitutional questions raised in the case over the federal government's most powerful tool to prevent discriminatory voting changes since the mid-1960s.

The law requires all or parts of 16 states, mainly in the South, with a history of discrimination in voting to get approval in advance of making changes in the way elections are conducted.

The court said that the Northwest Austin Municipal Utility District No. 1 in Austin, Texas, can opt out of the advance approval requirement, reversing a lower federal court that found it could not.

Chief Justice John Roberts, writing for the court, said the larger issue of whether dramatic civil rights gains means the advance approval requirement is no longer necessary "is a difficult constitutional question we do not answer today."

The court's avoidance of the larger issue explains the consensus among justices in the case rendered Monday, where they otherwise likely would have split along conservative-liberal lines.

Justice Clarence Thomas, alone among this colleagues, said he would have resolved the case and held that the provision, known as Section 5, is unconstitutional.

"The violence, intimidation and subterfuge that led Congress to pass Section 5 and this court to uphold it no longer remains," Thomas said.

The court ruled 6-3 Monday in favor of a teenage boy from Oregon whose parents sought to force their local public school district to pay the $5,200 a month it cost to send their son to a private school.

Federal law calls for school districts to reimburse students or their families for education costs when public schools do not have services that address or fulfill the students' needs. Under the Individuals with Disabilities Education Act, the nation's special education students are entitled to a "free and appropriate public education."

Schools have argued that parents of special education students should have given public special education programs a chance before seeking reimbursement for private school tuition. But advocacy groups and parents of some special education students contend that forcing them to try public schools first could force children, especially poor ones, to spend time in an undesirable situation before getting the help they need.

In the case before the Supreme Court, the family of a teenage Oregon boy diagnosed with attention deficit hyperactivity disorder sued the school district, saying the school did not properly address the student's learning problems. The family is seeking reimbursement for the student's tuition, which cost $5,200-a-month. The family paid a total of $65,000 in private tuition.

In its appeal, the Forest Grove School District said students should be forced to at least give public special education programs a try before seeking reimbursement for private tuition.

Justice John Paul Stevens said in his majority opinion that the federal Individuals with Disabilities Education Act requires a school district to pay for private special ed services if the public school doesn't have appropriate services.

"We conclude that IDEA authorizes reimbursement for the cost of special education services when a school district fails to provide a FAPE and the private-school placement is appropriate, regardless of whether the child previously received special education or related services through the public school," Stevens said.

The justices, acting Monday, say they will consider the Obama administration's appeal of a lower court ruling that invalidated the law.

The 4th U.S. Circuit Court of Appeals in Richmond, Va., ruled in January that Congress overstepped its authority when it enacted a law allowing for indefinite commitment of people who are considered "sexually dangerous."

In April, Chief Justice John Roberts granted an administration request to block the release of up to 77 inmates at a federal prison in North Carolina. These were people whose prison terms for sex offenses were ending. The justice's order was designed to allow time for the high court to consider the administration's appeal.

The challenge to the law was brought by four men who served prison terms ranging from three to eight years for possession of child pornography or sexual abuse of a minor. Their confinement was supposed to end more than two years ago, but the government determined that there would be a risk of sexually violent conduct or child molestation if they were released.

A fifth man who also was part of the legal challenge was charged with child sex abuse, but declared incompetent to stand trial.

Philip Markoff, the former medical student accused of killing a 25-year-old masseuse he met through Craigslist is being arraigned in Boston today for first-degree murder and other charges.

Philip Markoff is expected to be in Suffolk Superior Court on Monday morning. He was indicted by a grand jury Thursday after a two-month investigation.

Suffolk County District Attorney Daniel Conley told CBS' The Early Show Monday that his office continues to receive new information on the case, though he admitted most of it has been unhelpful.

Despite that, Conley said, "We believe that we've built a very strong case against this defendant."

He added that Markoff's fiancée, Megan McCallister, has been cooperative, but declined to say whether she would be a witness for the prosecution.

Conley said the case probably won't reach trial for at least a year.