President Biden, stepping back from a campaign vow, has embraced a longstanding U.S. approach of using the threat of a potential nuclear response to deter conventional and other nonnuclear dangers in addition to nuclear ones, U.S. officials said Thursday.

During the 2020 campaign Mr. Biden promised to work toward a policy in which the sole purpose of the U.S. nuclear arsenal would be to deter or respond to an enemy nuclear attack.

Mr. Biden’s new decision, made earlier this week under pressure from allies, holds that the “fundamental role” of the U.S. nuclear arsenal will be to deter nuclear attacks. That carefully worded formulation, however, leaves open the possibility that nuclear weapons could also be used in “extreme circumstances” to deter enemy conventional, biological, chemical and possibly cyberattacks, said the officials.

The decision comes as Mr. Biden is meeting with allies in Europe in an effort to maintain a unified Western stance against Russian President Vladimir Putin’s invasion of Ukraine and allied concerns that the Kremlin might resort to nuclear or chemical weapons.

A spokeswoman for the president’s National Security Council declined to comment.

Mr. Biden’s nuclear policy follows an extensive Nuclear Posture Review, in which administration officials examined U.S. nuclear strategy and programs.

U.S. officials said the administration’s review is also expected to lead to cuts in two nuclear systems that were embraced by the Trump administration. If Congress agrees, this would mean canceling the program to develop a nuclear sea-launched cruise missile and retiring the B83 thermonuclear bomb.

The review, however, supports the extensive modernization of the U.S. nuclear triad of land-based missiles, submarine-based missiles and bombers, which is projected to cost over $1 trillion.

During the Cold War, the U.S. reserved the right to use nuclear weapons in response to a conventional attack to offset the Soviet bloc’s numerical advantage in conventional forces. After giving up its chemical and biological weapons in accordance with arms-control treaties, the U.S. later said it was reserving the right to use nuclear weapons to deter attacks with poison gas and germ weapons in some circumstances.

North Atlantic Treaty Organization allies have been particularly nervous about shifting to a “sole purpose” doctrine, fearing it could weaken deterrence against a conventional Russian attack on the alliance.

Congressional Republicans had criticized Mr. Biden for considering a “sole purpose” doctrine.

In January, Sen. James Inhofe of Oklahoma and Rep. Mike Rogers

of Alabama, the ranking Republican members on the Senate and House Armed Services Committees, urged Mr. Biden to stay with the U.S. nuclear doctrine that they said had deterred major wars and the use of nuclear weapons for more than 70 years.

In contrast, a number of Democratic arms-control supporters had urged Mr. Biden to minimize the role of nuclear weapons in the Pentagon’s strategy and stipulate that the U.S. would never make the first use of nuclear weapons in a conflict.

“Allies were concerned that moving too far away from current posture would leave them vulnerable—in theory or in practice—to Russian threats,” said Jon Wolfsthal, who served as the senior arms control and nonproliferation official on President Obama’s National Security Council.

Mr. Wolfsthal, who served as an adviser to Mr. Biden when he was vice president, said it would be disappointing but not surprising if the president shelved his “sole purpose” initiative.

Some Biden administration officials say, however, that his decision doesn’t diminish his long-term goal to reduce the U.S. dependence on nuclear weapons and reflects the need to consolidate allied support in the face of Russian threats and a rising China.

Mr. Biden, these officials also note, has supported other arms-control moves, including prolonging the New START treaty limiting U.S. and Russian long-range arms, which he extended for five years.

During the 2020 campaign, Mr. Biden wrote in Foreign Affairs magazine that he believed “the sole purpose of the U.S. nuclear arsenal should be deterring—and, if necessary, retaliating against—a nuclear attack.”

Mr. Biden added that as president he would move “to put that belief into practice, in consultation with the U.S. military and U.S. allies.’’ Mr. Biden had also staked out a similar position before leaving his post of vice president in 2017.

“Given our nonnuclear capabilities and the nature of today’s threats, it’s hard to envision a plausible scenario in which the first use of nuclear weapons by the United States would be necessary,” Mr. Biden said at the time.

The reason for his “sole purpose” proposal was to narrow the circumstances in which the U.S. would consider using nuclear weapons by excluding the possibility that they could be employed in response to a conventional attack or other nonnuclear threats.

Mr. Biden’s plan to overhaul U.S. doctrine and strategy, however, ran into firm opposition from allied nations, who were concerned that it might weaken the U.S. and allies’ ability to deter a conventional Russian or Chinese military offensive, according to foreign diplomats and U.S. officials.

The Biden administration “fundamental role” phrase harks back to the Nuclear Posture Review conducted in 2010 during the Obama administration.

But it differs somewhat from the more specific language in the Trump administration’s Nuclear Posture Review, which underscored the role of nuclear weapons to “hedge against an uncertain future.”

That review spelled out that the threat of nuclear weapons could be used to deter what the Trump administration called “nonnuclear strategic attacks” against U.S. or allied populations or infrastructure. That suggested that a major cyberattack, germ weapon or chemical attack that killed thousands of people could trigger a nuclear response.

Write to Michael R. Gordon at michael.gordon@wsj.com

Corrections & Amplifications
Jon Wolfsthal served on President Barack Obama’s National Security Council. An earlier version of this article incorrectly gave his name as Jon Wolfstahl. (Corrected on March 25)