For more than six months, President Biden and his aides have been wrestling with one of the most vexing questions in the war in Ukraine: whether to risk letting Ukrainian forces run out of the artillery rounds they desperately need to fight Russia, or agree to ship them cluster munitions — widely banned weapons known to cause grievous injury to civilians, especially children.
On Thursday, Mr. Biden appeared on the verge of providing the cluster munitions to Ukraine, a step that would sharply separate him from many of his closest allies, who have signed an international treaty banning the use, stockpiling or transfer of such weapons.
Several of Mr. Biden’s top aides, including Secretary of State Antony J. Blinken, recommended he make the move at a meeting of top national security officials last week, despite what they have described as their own deep reservations, people familiar with the discussions said. They requested anonymity to discuss sensitive deliberations.
The State Department had been the last holdout, both because of humanitarian concerns and worries that the United States would be drastically out of step with its allies.
Now, Mr. Biden’s aides think they have little choice.
Mr. Biden has come under steady pressure from President Volodymyr Zelensky of Ukraine, who argues that the munitions — which disperse tiny, deadly bomblets — are the best way to kill Russians who are dug into trenches and blocking Ukraine’s counteroffensive to retake territory. One American official said Thursday that it was now clear that the weapons are “100 percent necessary” to meet the current battlefield needs.
Yet for months, Mr. Biden and his aides have tried to put off the decision, hoping that the tide of the war would turn in Ukraine’s favor. Part of the concern has been that the United States would appear to lose the moral high ground, using a weapon that much of the world has condemned, and that Russia has used with abandon.
The administration has also been aware that sending the weapons to Ukraine would be enormously unpopular among allies and members of Mr. Biden’s own party; over the years, many Democrats have led the charge to bar the use of the weapons by American troops. When, five days into the war, Jen Psaki, then the White House press secretary, was asked about the Russian use of unconventional weapons, including cluster munitions, she said: “We have seen the reports. If that were true, it would potentially be a war crime.”
More than 100 nations have signed a 15-year-old treaty banning the use of cluster munitions, which rain down smaller bombs that scatter across the landscape. The weapons, which are meant to explode when they hit the ground, have caused thousands of deaths and injuries, often among children who have picked up duds that failed to go off in the initial attacks, only to explode long after a conflict is over.
Although White House officials said Thursday that Mr. Biden had not made a final decision, several officials said they expected he would give his final approval imminently. The timing is awkward for Mr. Biden, who heads to Europe for a NATO meeting in Vilnius, Lithuania, next week. It also comes as the United States moves to destroy other hazardous weapons — the last of its once-vast chemical weapons arsenal.
Most of Washington’s closest allies, including Britain, Germany and France, signed on to the United Nations Convention on Cluster Munitions in 2008. The United States, Russia and Ukraine have never signed the treaty, arguing that there are circumstances in which the weapons must be used, despite the potential for severe civilian casualties.
Mr. Biden was persuaded, officials said, after the Pentagon argued that they would provide Ukraine with an “improved” version of the weapon that has a “dud rate” of roughly 2 percent of all rounds fired.
Russia, officials noted, has been using its cluster munitions in Ukraine for much of the war, with a dud rate of 40 percent or more, creating a far larger hazard. The Ukrainians have also used cluster munitions, though their stockpile is a fraction of Washington’s.
Many bomb experts say the dud rates of American cluster munitions are likely far higher than Pentagon estimates.
“If they land in water, soft ground like plowed fields and muddy areas, that can certainly impact the reliability, causing higher dud rates,” said Al Vosburgh, a retired Army colonel trained in bomb disposal who runs a humanitarian mine action nonprofit organization.
On Thursday morning, Human Rights Watch issued a lengthy report on the use of cluster munitions in Ukraine. “Cluster munitions used by Russia and Ukraine are killing civilians now and will continue to do so for many years,” Mary Wareham, the organization’s acting arms director, wrote. “Both sides should immediately stop using them and not try to get more of these indiscriminate weapons.” In fact, the Ukrainians have been using the weapons since early in the war, often on their own territory.
American officials said that the fact that the Ukrainians decided that they preferred to use the weapons — whatever the costs — rather than live under Russian rule has become a critical factor in Mr. Biden’s thinking.
American officials also say they will work with Ukraine to track where the weapons are being used to aid in the cleanup of unexploded munitions.
Biden administration officials tried for months to scrounge up enough conventional artillery rounds to keep firing at Russian positions. But after convincing South Korea to chip in hundreds of thousands of rounds, and tapping American stockpiles of artillery shells stored in Israel, the Pentagon is projecting that Ukraine will run short.
American officials believe Mr. Putin is betting that his forces could seize that moment to prevail.
In interviews, American officials said they expected the shipment of the cluster munitions to be a temporary move, until production of conventional artillery shells can be ramped up, probably by the spring of next year.
The war in Ukraine has been at its core a battle of artillery, with both sides hurling huge numbers of shells at entrenched lines of soldiers in the country’s east and south. Early on in the war, Ukraine ran low on Soviet-era shells and since then has largely shifted to firing artillery guns and rounds donated by the United States and its allies.
Throughout this global scramble to keep Ukraine flush with ammunition, the Pentagon repeatedly reminded the White House that the United States was sitting on a mountain of untapped munitions that could ease the strain on the artillery shortages: cluster munitions.
And for months, Pentagon officials said on Thursday, the White House demurred, citing concerns about the weapons’ use and saying they were not necessary.
But as Ukraine’s counteroffensive has been met with stiffer-than-expected Russian defenses, U.S. officials recently signaled a shift.
Laura Cooper, the deputy assistant secretary of defense for Russia, Ukraine and Eurasia, told U.S. lawmakers late last month that the Pentagon had determined that cluster munitions would be useful for Ukraine, “especially against dug-in Russian positions on the battlefield.”
Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, last Friday confirmed published reports that the Biden administration was considering sending to Ukraine cluster munitions and a powerful weapon called the Army Tactical Missile System, or ATACMS. Mr. Biden has refused to send the missile system until now, partly because the weapon could reach deep into Russia.
In a series of recent interviews, Mr. Zelensky has repeated his plea for more arms, even as the United States has committed more than $40 billion in arms, ammunition and equipment since the war started.
“The first issue is, of course, ammunition,” Mr. Zelensky told The Washington Post in May.
Mr. Zelensky told CNN in a broadcast on Wednesday that Ukraine’s counteroffensive has been “slowed down” by entrenched Russian defenses and that it would have started “much earlier” had Western weapons arrived faster.
John Ismay contributed reporting.