WASHINGTON — In the long legal struggle against the death penalty, the future has in some ways never looked brighter.

In a passionate dissent in June, Justice Stephen G. Breyer invited a major challenge to the constitutionality of capital punishment. This fall, Justice Antonin Scalia all but predicted that the court’s more liberal justices would strike down the death penalty.

But lawyers and activists opposed to the death penalty, acutely conscious of what is at stake, are bitterly divided about how to proceed. Some say it is imperative to bring a major case to the court as soon as practicable. Others worry that haste may result in a losing decision that could entrench capital punishment for years.

If you don’t go now, there’s a real possibility you have blood on your hands,” said Robert J. Smith, a fellow at the Charles Hamilton Houston Institute of Harvard Law School. His scholarship was cited in Justice Breyer’s dissent from a decision upholding the use of an execution drug that three death row inmates argued risked causing excruciating pain.

But others are wary. “There are reasons to be cautious about pushing the court to a decision too early,” said Jordan M. Steiker, a law professor at the University of Texas.

The divide is partly generational. Many veteran litigators have suffered stinging setbacks in the Supreme Court, and they favor an incremental strategy. They would continue to chip away at the death penalty in the courts, seek state-by-state abolition and try to move public opinion.

Some younger lawyers and activists urge a bolder course: to ask theSupreme Court to end capital punishment nationwide right away.

Though Justice Breyer’s dissent was joined only by Justice Ruth Bader Ginsburg, the more aggressive advocates are confident they can persuade five justices to do away with a punishment explicitly contemplated in theFifth and 14th Amendments, which call for grand juries in federal cases involving “a capital or other infamous crime” and say that no person may be deprived “of life, liberty or property, without due process of law.” That means picking up the votes of not only the rest of the court’s liberal wing — Justices Sonia Sotomayor and Elena Kagan — but also, crucially, Justice Anthony M. Kennedy.

Evan J. Mandery, the author of “A Wild Justice,” a history of the last major challenges to the death penalty in the 1970s, said there were good arguments on both sides of whether to mount such an effort.

“It’s a very complicated gamble,” he said. “The fear is that if you push and you lose, you could end up worse off.”

All concerned agree that much has changed since the Supreme Court reinstated the death penalty in 1976, four years after it had effectively struck it down. Last year, only seven states carried out executions. Nineteen states and the District of Columbia have abolished the death penalty entirely, seven of them in the last decade.

Governors and courts have imposed moratoriums in others, and the number of death sentences and executions continues to drop. The Supreme Court itself has barred the execution of juvenile offenders, people with intellectual disabilities and those convicted of crimes against individuals other than murder in the last decade.

The more cautious, step-by-step approach would ask the court to further narrow the availability of the death penalty by, for instance, forbidding the execution of mentally ill people and of accomplices who did not kill anyone. The more assertive one would introduce a broad case aimed at the death penalty itself.

Both sides look to history for instruction, but they draw different lessons.

Justice Breyer has told friends that his dissent was partly inspired by a similar one a half-century before. The earlier dissent, by Justice Arthur J. Goldberg, helped create the modern movement for the abolition of the death penalty and led to a four-year moratorium on executions.

The 1963 dissent, in Rudolph v. Alabama, was drafted by a law clerk, Alan M. Dershowitz, who would go on to become a law professor at Harvard and a prominent litigator. A young Stephen G. Breyer began his own clerkship with Justice Goldberg the year after.

Collecting data on national and international practice, Justice Goldberg’s dissent urged the court to hear a case on whether the death penalty for rape violated the Eighth Amendment’s ban on cruel and unusual punishment.

“The goal was to ask litigators to start raising challenges to the death penalty,” Professor Dershowitz said. “It was an invitation to litigation. It was not a common tactic back then, and we were much criticized for it.”

The dissent spurred the creation of capital litigation projects at the NAACP Legal Defense and Educational Fund and at the American Civil Liberties Union.

Justice Breyer’s dissent was far more elaborate. It was 46 pages long, included charts and maps, and set out in detail the argument that the death penalty violated the Eighth Amendment’s ban on cruel and unusual punishments.

Professor Dershowitz said he was delighted that another former clerk of Justice Goldberg’s was carrying on his old boss’s project.

“The goal in both cases is to encourage the court to play a more active role and to encourage litigants,” he said.

But opinions vary about the correct reading of the aftermath of the Goldberg dissent. Some veteran opponents of the death penalty noted that it took nine years of methodical litigation after the 1963 dissent before the Supreme Court effectively struck down the death penalty in 1972 inFurman v. Georgia. Even then, they said, the effort in the end yielded only a relatively brief moratorium.

Sherrilyn Ifill, the president of the NAACP Legal Defense and Educational Fund, which has long played a central role in the fight against the death penalty, chose her words carefully in response to questions about her group’s current strategy.

Death Penalty Foes Split Over Taking Issue to Supreme Court