WASHINGTON — Even before the start of the war in Ukraine, an international alliance to rally the world against a Russian invasion came together so quickly that President Biden later marveled at the “purpose and unity found in months that we’d once taken years to accomplish.”

Now, with the conflict in its fourth month, U.S. officials are facing the disappointing reality that the powerful coalition of nations — stretching from North America across Europe and into East Asia — may not be enough to break the looming stalemate in Ukraine.

With growing urgency, the Biden administration is trying to coax or cajole countries that have declared themselves neutral in the conflict — including India, Brazil, Israel and the Gulf Arab states — to join the campaign of economic sanctions, military support and diplomatic pressure to further isolate Russia and bring a decisive end to the war. So far, few if any of them have been willing, despite their partnerships with Washington on other major security matters.

Mr. Biden is making an extraordinary diplomatic and political gamble this summer in planning to visit Saudi Arabia, which he had called a “pariah.” And on Thursday, he met with President Jair Bolsonaro of Brazil on the sidelines of the Summit of the Americas in Los Angeles. Mr. Bolsonaro visited Moscow the week before Russia invaded Ukraine and declared “solidarity” with President Vladimir V. Putin.

In Los Angeles, Mr. Bolsonaro pre-empted any push by Mr. Biden on Russia, saying that while Brazil remained open to helping end the war, “given our reliance on certain foreign players, we have to be cautious.”

“I have a country to manage,” he said.

U.S. officials acknowledge the difficulties in trying to convince countries that they can balance their own interests with the American and European drive to isolate Russia.

“One of the biggest problems that we are facing today is the fence-sitter problem,” Samantha Power, the head of the U.S. Agency for International Development, said on Tuesday after giving a speech about the administration’s efforts to reinforce free speech, fair elections and other democratic systems against authoritarian leaders worldwide.

She said she was hopeful that Russian atrocities committed in Ukraine would persuade neutral states to join the coalition against Moscow, “given our collective interest in rules of the road that all of us would wish to see observed, and none of us would wish to see used against our citizens.”

Russia and its partners, notably China, have denounced the U.S. government’s efforts to expand the coalition, which in addition to European nations also includes Canada, Japan, South Korea, Australia and New Zealand.

“In the modern world, it is impossible to isolate a country, especially such a huge one as Russia,” Mr. Putin’s spokesman, Dmitry Peskov, said on Thursday, according to state media.

In Beijing, Zhao Lijian, a Chinese Foreign Ministry spokesman, said on Monday that the United States “forced countries to take sides in the conflict between Russia and Ukraine and wantonly threatened to impose unilateral sanctions and long-arm jurisdiction.” He added: “Isn’t this coercive diplomacy?”

Russia’s currency, the ruble, cratered shortly after Mr. Putin launched the invasion of Ukraine in February. But it has since bounced back as Russia continues earning hard currency from exporting energy and other goods to many nations, including China, India, Brazil, Venezuela and Thailand.

For some countries, the decision of whether to align with the United States can have life-or-death consequences. Washington has warned drought-stricken African nations not to buy grain that Russia stole from Ukraine at a time when food prices are rising and possibly millions of people are starving.

“Key strategic middle powers such as India, Brazil and South Africa are consequently treading a very sharp line in an attempt to preserve their strategic autonomy and cannot be expected to simply sidle up to the U.S.,” said Michael John Williams, a professor of international relations at Syracuse University and a former adviser to the North Atlantic Treaty Organization.

“Washington believes this war will be won in the West,” Mr. Williams said, “but the Kremlin believes it will be won in the East and the Global South.”

In a vote in March on a United Nations resolution condemning Russia’s aggressions against Ukraine, 35 countries abstained, mostly from the Middle East, Africa and South Asia. That alarmed American officials and their allies, who nonetheless noted that 141 of 193 states censured Russia. Only five states — including Russia — voted against the measure.

Brazil voted to condemn Russia, and Mr. Bolsonaro has pressed for negotiations to end the war. But his country continues to import fertilizer from Russia and Belarus, an ally of Moscow.

India and South Africa both abstained from the U.N. vote. India has a decades-long strategic partnership with Russia and relies on it for oil, fertilizer and military equipment. The Biden administration has had little luck getting India to join its coalition.

Indian officials say their Russian imports are modest. During a visit to Washington in April, India’s foreign minister, Subrahmanyam Jaishankar, dismissed questions on the subject, saying that “probably our total purchases for the month would be less than what Europe does in an afternoon.”

“So you might want to think about that,” he said.

But Europe is now slashing its energy imports, in a partial embargo of Russian oil, while India is reportedly in talks with Moscow to further increase its already growing purchases of crude oil.

South Africa’s ties to Russia go back to the Cold War, when the Soviet Union supported the anti-apartheid movement that transformed the nation’s internal power dynamics.

Trade between the two countries is modest, but South Africa, like many other nations, has long been suspicious of Western colonialism and the United States as an unrivaled superpower. President Cyril Ramaphosa of South Africa has accused NATO of provoking Russia into war and has called for renewed diplomatic talks. In a phone call in April, Mr. Biden urged him to accept “a clear, unified international response to Russian aggression in Ukraine,” according to a White House statement.

A month later, Mr. Ramaphosa lamented the impact that the conflict was having on “bystander” countries that he said “are also going to suffer from the sanctions that have been imposed against Russia.”

Brazil, India and South Africa — along with Russia and China — are members of a group of nations that account for one-third of the global economy. At an online meeting of the group’s foreign ministers last month, Moscow offered to set up oil and gas refineries with its fellow partners. The group also discussed expanding its membership to other countries.

Other nations that abstained from the United Nations vote, including Uganda, Pakistan and Vietnam, have accused the U.S.-led coalition against Russia of shutting down any chance of peace talks with its military support of Ukraine. U.S. and European officials maintain that the weapons and intelligence it has provided serves only to help Ukraine defend itself from Russia’s military.

The growing urgency in the Biden administration is embodied in the president’s plans to visit Saudi Arabia, despite his earlier denunciations of its murderous actions and potential war crimes. Mr. Biden’s effort, which is already being criticized by leading Democrats, is partly aimed at getting Saudi Arabia and the United Arab Emirates to help on the margins with Ukraine. One goal is to have those nations coordinate a substantial increase in oil production to help bring down global prices while the United States, Europe and others boycott Russian oil.

U.S. officials have been disappointed by the proclaimed neutrality of the two Gulf Arab nations, which buy American weapons and lobby Washington for policies against Iran, their main rival.

Israel, which also buys American weapons and is the United States’ closest ally in the Middle East, has expressed solidarity with Ukraine. At the same time, however, it has resisted supporting some sanctions and direct criticism of Russia.

Until Mr. Biden offered to meet with him in Los Angeles, Mr. Bolsonaro had signaled he would not go to the summit of most of the hemisphere’s heads of state. It took a direct appeal by former Senator Christopher J. Dodd of Connecticut, a special adviser to the summit, to convince Brazil to attend.

Valentina Sader, a Brazil expert at the Atlantic Council, said the Biden administration was expected to continue talking to Mr. Bolsonaro about Brazil’s ties with Russia and China.

But, she said, it was unlikely that Mr. Bolsonaro would edge away from Mr. Putin. “Brazil is taking its own interests into account,” Ms. Sader said.

American officials have come to the same conclusion about China, which is Russia’s most powerful strategic partner. They say China has clearly chosen to stand with Russia — as evidenced by the constant reiteration by Chinese officials of Mr. Putin’s criticisms of the United States and NATO and their spreading of disinformation and conspiracy theories that undermine the United States and Ukraine.

On Feb. 4, three weeks before Russia began its full-scale invasion, Mr. Putin and President Xi Jinping of China met in Beijing while the two governments declared a “no limits” partnership.

In late May, China and Russia held their first joint military exercise since the war in Ukraine began — flying strategic bombers over the seas of northeast Asia while Mr. Biden was visiting Japan.

But China has also held back from giving economic or military aid to Russia, despite requests from Moscow, U.S. officials say. Mr. Biden warned Mr. Xi in a video call in March that there would be “consequences” if China gave material aid to Russia, and Chinese officials and business executives fear that their companies could be hit with sanctions if the firms give Russia substantial support.

“Secondary sanctions do bite, and China doesn’t want this to affect their companies,” said Alexander Gabuev, a senior fellow at the Carnegie Endowment for International Peace who was recently based in Moscow. “Many Russian sources tell me they talk to the Chinese and are not hearing anything back.”

Michael Crowley contributed reporting.