A Supreme Court term that is starting with a lack of headline-grabbing cases may end with a blockbuster that helps define the legacy of the court under Chief Justice John Roberts.

While same-sex marriage is not yet on their agenda, the justices appear likely to take on the issue and decide once and for all whether gay and lesbian couples have a constitutional right to marry.

When the justices formally open their new term Monday, Roberts will be beginning his 10th year at the head of the court, and the fifth with the same lineup of justices. He has been part of a five-justice conservative majority that has rolled back campaign finance limits, upheld abortion restrictions and generally been skeptical of the consideration of race in public life.

But his court has taken a different path in cases involving gay and lesbian Americans, despite his opposition most of the time.

The court's record on gay rights is comparable to its embrace of civil rights for African-Americans in the 1950s and 1960s under Chief Justice Earl Warren, said University of Chicago law professor David Strauss. "The court will go down in history as one that was on the frontiers of establishing rights for gays and lesbians," Strauss said.

The justices passed up their first opportunity last week to add gay marriage cases to their calendar. But they will have several more chances in the coming weeks to accept appeals from officials in Indiana, Oklahoma, Utah, Virginia and Wisconsin who are trying to preserve their state bans on same-sex marriage.

Those prohibitions fell one after the other following the high court's June 2013 decision that struck down part of a federal law that defined marriage as between a man and a woman.

On the court's plate in the new term are cases involving:

--religious, employment and housing discrimination.

--the drawing of political districts in Alabama and Arizona.

--a dispute between Congress and the president over passports that is heavy with Middle East politics.

--a faulty traffic stop over a car's broken brake light in North Carolina.

--the use of a law to prevent document shredding against a fisherman accused of throwing undersized red grouper overboard.

--the prosecution of a self-styled rapper whose Facebook postings threatened his estranged wife, an FBI agent and area schools.

Monday's argument involves the North Carolina traffic stop that led to the discovery of cocaine in Nicholas Heien's Ford Escort. A police officer pulled over the car when he saw the right brake light wasn't working, although the left one was. Typically, evidence found in a car pulled over for a valid reason can be used against a defendant. But North Carolina's quirky traffic laws mandate that only one brake light on a car be working.

The case tests whether the officer's mistaken understanding of the law makes the traffic stop unreasonable and the ensuing search a violation of Heien's constitutional rights. Among Heien's arguments is that citizens can't plead ignorance of the law when they are charged with a crime, so there shouldn't be a double standard for the police. A divided state Supreme Court said the mistake was reasonable enough to justify the routine traffic stop.

On Tuesday, the justices will take up the case of Arkansas prison inmate Gregory Holt, who says his Muslim beliefs require him to grow a half-inch beard. Arkansas prison officials permit no beards, with the exception of inmates with certain skin conditions, who can have beards a quarter-inch long.

Prison officials say their rule is a matter of security because beards can be used to hide prohibited items, and 18 states are backing the state's argument. But groups across the political spectrum and the Obama administration say Holt has a right to grow a beard under a federal law aimed at protecting prisoners' religious rights. More than 40 states already allow beards, with little evidence that inmates have tried to hide prohibited items in them.

Last term, the court bitterly divided over the religious rights of family-owned corporations that objected to paying for women's contraceptives under President Barack Obama's health care law. This case appears likely to unite the court, said University of Notre Dame law professor Richard Garnett. "I think there's every reason to expect agreement among the justices that Arkansas hasn't even come close to satisfying the burden," Garnett said.

The court's calendar this fall also includes a foray into the online world. Anthony Elonis of Bethlehem, Pennsylvania, is challenging his conviction for using Facebook to post threats of violence. The issue in Elonis' case is whether he had to intend to make the threats. The government argues that the proper measure is whether a reasonable person would feel threatened.

Elonis said his online postings should be considered speech that is protected by the First Amendment, and that he used the forum to vent his frustration over a series of events that included the loss of his job and the breakup of his marriage.

Beyond individual cases on the docket, court observers across the political spectrum are using the milestone 10th year to offer assessments of Roberts and the court he leads.

The liberal Constitutional Accountability Center has embarked on a yearlong study of the chief justice, noting that he said at his confirmation hearings he would pursue restraint and unanimity on the bench.

Some conservatives are dismayed by what they see as Roberts' unwillingness to take big steps on key issues, and they have yet to forgive his vote to uphold Obama's health care law in 2012.

With the court closely divided on key issues, a change on the bench can mean the difference between victory and defeat. That was indeed the case with the replacement of Justice Sandra Day O'Connor with Justice Samuel Alito, affecting outcomes in cases on abortion, race and campaign finance.