WASHINGTON – President Obama’s top national security advisers within days will present him with an agonizing choice on how to guide U.S. nuclear weapons policy for the rest of his presidency.

Does he substantially advance his bold pledge to seek a world free of nuclear weapons by declaring that the “sole purpose” of the U.S. arsenal is to deter other nations from using them? Or does he embrace a more modest option, supported by some senior military officials, that deterrence is the “primary purpose”?

The difference may seem semantic, but such words, which will be contained in a document known as the Nuclear Posture Review, have deep meanings and could dramatically shift nuclear policy in the United States and around the world.

The first option would scale back the arsenal’s war-fighting role, potentially leading to a smaller U.S. stockpile and taking weapons off alert. The second option would be less of a change, holding out the nuclear threat but still permitting a reduction in weapons. The president was briefed on the document this week and requested additional intermediate options, officials say.

Senior administration officials have already indicated the review is likely to roll back some Bush policies, such as threatening the use of nuclear weapons to preempt or respond to chemical or biological attacks. The review will also point to new ways to cut the Pentagon’s stockpile of roughly 5,000 active nuclear warheads, they say.

But, officials say, after lengthy debate, Obama’s aides have rejected some of the boldest ideas on the table, such as forswearing the option to use nuclear arms first in a conflict, or dropping one leg of the “triad” of bombers, submarines and land-based missiles that carry the deadly weapons.

Obama’s decision on the sensitive issue of U.S. “declaratory policy,” U.S. officials and outside experts say, will help determine whether the document is regarded as a far-reaching shift from the Bush administration’s version released in 2001. Lower-level officials trying to craft the language engaged in fierce discussions about how far and fast the administration could alter course without alarming allies.

The Nuclear Posture Review is done at the start of each administration, and influences budgets, treaties and weapons deployments and retirements for five to 10 years. Expectations for this one have been raised because of Obama’s pledge last year to “put an end to Cold War thinking” and move toward global disarmament — a vision that helped win him a Nobel Peace Prize.

The review, more than a month overdue, reflects the tension in seeking to advance the president’s sweeping agenda without unnerving allies who depend on the U.S. nuclear “umbrella.” The Pentagon is also wary of losing options in a world with emerging nuclear threats from North Korea and Iran, officials say.

Until recently, Obama generally has not intervened in the Pentagon-led process, which also involves officials from the State Department, the Energy Department and other agencies. That has raised concerns among arms-control advocates that the final product will be a cautious bureaucratic compromise.

U.S. diplomats hope the final document will establish the Obama administration’s credibility before a nuclear security summit in April and a crucial meeting in May on the fraying global nuclear Non-Proliferation Treaty. That treaty is at the heart of Obama’s strategy to combat the most urgent threat today: the spread of nuclear weapons to unstable states and to terrorists.

The last such session in 2005 ended in failure, with many countries accusing the Bush administration of trying to scotch their nuclear programs while maintaining one of the world’s most massive stockpiles.

“The United States can’t go around and ask others to give up their nuclear weapons while we maintain a list of official purposes for our nuclear weapons” that necessitates a large arsenal, said Jan Lodal, a senior Defense Department official in the Clinton administration.

Pentagon officials worry that allies like Japan or Turkey could decide to develop their own nuclear weapons if they believed U.S. protection wasn’t assured. Skeptics — both Democrats and Republicans — also question whether pledges to limit the U.S. nuclear role would have the impact claimed by proponents, since foes probably wouldn’t believe such assertions.

“We’re better off when we communicate that all options are on the table,” said Thomas Mahnken, a senior Defense Department official in the Bush administration. “As a practical matter, they are.”

More than two dozen Democrats, led by Sen. Dianne Feinstein, Calif., chairwoman of the Intelligence Committee, have pressed Obama to adopt language saying the “only” purpose of U.S. nuclear weapons is deterrence. It would not prevent the U.S. government from using a weapon first but would de-emphasize that option in planning.