Chinese leader Xi Jinping is planning to visit Saudi Arabia before the end of the year, according to people familiar with preparations for the trip, as Beijing and Riyadh seek to deepen ties and advance a vision of a multipolar world where the U.S. no longer dominates the global order.

Officials are completing the details for a summit between Mr. Xi and Saudi Crown Prince Mohammed bin Salman that would underline Beijing's growing influence in the Middle East, where the U.S. long reigned supreme, and growing links between the oil-rich Saudis and Washington's top global rivals.

In the works for months, the trip is tentatively scheduled for the second week of December, these people said.

China's Foreign Ministry, in a faxed response to a request for comment, said it had no information to share, but affirmed Beijing's willingness "to work with Saudi Arabia to continuously consolidate mutual trust and deepen cooperation, and to push the China-Saudi comprehensive strategic partnership for greater achievements."

Beijing "attaches great importance to the development of China-Saudi relations, and places Saudi Arabia as a priority in China's overall diplomatic policy," Chinese Foreign Minister Wang Yi said late last month. Chinese-Saudi relations have deepened in recent years in the economic realm, including a potential Chinese stake in state oil giant Saudi Aramco, and militarily through weapons sales.

The meeting comes at a time when large parts of the developing world have expressed reluctance to choose sides in the war between Russia and Ukraine, which has received Western backing, despite urging from Washington and European capitals.

Riyadh, in particular, has expressed a desire to put its own interests first on oil policy, in a way it says isn't intended to benefit Russia. Saudi Arabia pushed for a significant cut in output by the OPEC+ group of oil-producing nations in an effort to keep petroleum prices from falling.

Crown Prince Mohammed bin Salman is seeking to diversify Saudi Arabia's economy away from its dependence on oil.

Higher prices for oil—a major Russian export—help Moscow pay for its war effort. The production cut last month also raised crude prices at a moment of high inflation just before the U.S. midterm elections, straining the kingdom's relationship with Washington.

Saudi officials reject U.S. assertions that they are aligning with Moscow and say they don't want to be forced to take sides between world powers as they did during the Cold War, when Saudi Arabia stood squarely in the American camp.

"There is this sort of realignment happening: Where does your future lie?" said Helima Croft, managing director of global commodity strategy research at RBC Capital Markets. For the Saudis, she said, "It is pushing them more toward a multifaceted set of relationships. They see their future in the East."

With the world's second-largest economy and a shared interest in countering the West, China might be Moscow's most important partner as the Kremlin weathers Western economic sanctions and declining oil exports to Europe. Beijing hasn't condemned the invasion and has accused the U.S. of inflaming the crisis but said it isn't selling weapons to Russia.

Saudi Arabia has condemned the invasion and sent humanitarian aid to Ukraine but also sustained its oil alliance with Russia.

The strategic recalibration of Saudi foreign policy is bigger than the recent blowup with the Biden administration over oil production, said Ian Bremmer, president of the political-risk firm the Eurasia Group, as Riyadh looks for a counterweight to dependence on the U.S.

"This orientation of the Saudis and the Chinese towards each other is a long-term tipping point shift that is really going to matter economically, not just for this election cycle," said Mr. Bremmer.

What would be the impact of expanded geopolitical ties between China and Saudi Arabia? Join the conversation below.

The Saudis once sold the U.S. over 2 million barrels of oil a day, but that has fallen to less than 500,000, according to the U.S. Energy Information Administration. The U.S. grew to become the world's biggest oil producer, and China is now the biggest buyer of Saudi oil, followed by India.

The world's top oil importer and biggest oil exporter are likely to meet at an important moment for global energy markets that could determine the future of Russia's war effort.

Just before the Chinese leader lands in Saudi Arabia, the OPEC+ alliance led by Riyadh and Moscow will make a highly anticipated decision on crude production on Dec. 4, after cutting output by 2 million barrels last month. That will be followed by the planned implementation of a price cap on Russian oil by the Group of Seven leading nations and a European Union embargo on Russian crude.

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Officials in Riyadh, the Saudi capital, are recalibrating foreign policy in ways that undermine U.S. influence in the kingdom.

Mr. Xi, who last month cemented his role as China's leader for a third term, is expected to meet the leaders of other Persian Gulf and Arab countries in a visit that will likely feature pageantry and agreements demonstrating the countries' deepening partnership.

When President Biden visited Saudi Arabia in July, he met with Prince Mohammed and joined a summit of friendly Arab nations but faced intense scrutiny back home over Riyadh's human-rights records and came away with few concrete achievements.

The Chinese leader's welcome is more likely to resemble the 2017 visit by then-President Donald Trump, who was feted by Prince Mohammed on his first trip abroad and then largely backed the Saudis, according to people familiar with the preparations.

Formal relations between China and Saudi Arabia only began in 1990 and were restricted mainly to oil: Saudi Arabia is China's top supplier of crude and China is Saudi Arabia's biggest customer, buying one out of every four barrels of oil the kingdom sells.

More recently, their courtship has intensified with discussions on selling a stake in Saudi Aramco, including yuan-denominated futures contracts in Aramco's pricing model, and possibly pricing some Saudi oil sales to China in yuan.

Saudi Arabia is China's top supplier of crude, and China is Saudi Arabia's biggest customer.

Saudi Arabia, the custodian of Islam's holiest sites, has publicly defended China's policies in its western region of Xinjiang, giving cover to its crackdown on the Uyghur Muslim minority. At home, it is introducing Mandarin into the Saudi school curriculum.

China hasn't demonstrated interest or ability in supplanting the broad American role in the Middle East, analysts say, and the Saudis don't really want to replace the U.S. as their main security guarantor.

But Beijing has sold drones to Saudi Arabia, helped it manufacture ballistic missiles after the U.S. refused to do so over proliferation concerns, and helped construct a facility in the kingdom to fabricate uranium yellowcake, an early step along the path to a civil nuclear energy program or a nuclear-arms capability. The countries have also discussed building a naval base on the Red Sea, one of the world's most strategic waterways.

Beijing maintains warm relations with Saudi Arabia's rival Iran, which Riyadh could seek to leverage if Tehran agrees to a revived nuclear deal with the U.S. and other world powers.

President Biden and Saudi Crown Prince Mohammed bin Salman met in Saudi Arabia in July.

The sense of China's growing influence in the Middle East changes the calculus for Washington policy makers, who want to pivot to Asia but are loath to let Beijing establish a foothold in the strategic crossroads leading to Europe and Africa, said Jonathan Fulton, assistant professor of political science at Abu Dhabi-based Zayed University who studies China's relations with Gulf states.

"If the U.S. finds it harder to leave the Gulf, that would be in China's favor," he said. "China probably thinks that nursing those perceptions helps."

The China-Saudi relationship, while still largely transactional, has grown beyond just being a hedge for Riyadh to signal its displeasure with Washington, said Dr. Fulton.

The Saudis "aren't trying to play one off the other so much as really trying to deepen what they're getting out of both sides," he said. "The U.S. has this binary right now, where it's strategic competition: work with us or work with China. But most actors in the Gulf don't seem to see it that way."

Write to Stephen Kalin at stephen.kalin@wsj.com, Keith Zhai at keith.zhai@wsj.com and Summer Said at summer.said@wsj.com