WASHINGTON — The US is expected to announce Thursday it will send Ukraine a second Patriot missile system, giving the country a vital air defense boost that its president, Volodymyr Zelensky, has said could drastically reduce the number of successful Russian strikes.

Two US officials confirmed to The Post that President Biden had approved the move, which will see the Pentagon donate a Patriot system that has been protecting NATO territory and US troops in Poland throughout Russia’s 28-month-old war on Ukraine.

The New York Times first reported on the expected transfer.

The powerful Patriot systems have been influential in keeping Ukraine in the fight by providing robust defense against incoming threats from the air, including missiles and aircraft. They have been particularly key in fending off attacks on Kyiv, helping Ukraine’s capital to remain standing amid the Russian onslaught.

The systems come on wheels, so Ukraine has been moving them throughout the country as needed to both protect key target areas and prevent Russian forces from locating and taking out the batteries.

In March, Ukrainian soldiers on the ground told The Post that their scarce supply means they must make difficult choices between protecting civilians in major cities or troops on the battlefield.

“With these additional air defenses, Ukraine would be better equipped to defend its cities and critical infrastructure and would gain greater flexibility to push Patriot batteries closer to the front lines to ambush Russian aircraft,” Foundation for Defense of Democracies’ Russia program deputy director John Hardie told The Post on Wednesday.

The Pentagon does not make public how many Patriots the US has in its arsenal due to their critical nature. However, one senior military official told the Times that the Army has deployed just 14 across the country and around the world.

Biden and Zelensky are scheduled to meet Thursday on the sidelines of the G7 summit in Italy, while Defense Secretary Lloyd Austin will host the monthly meeting of the Ukraine Defense Contact Group in Brussels ahead of a NATO defense ministerial meeting Friday.

The US move comes after other NATO partners, including Germany and the Netherlands, have announced shipments of the systems to Ukraine.

While the new shipment is encouraging for Ukraine, its forces will still not have enough to fully fend off Russia’s continued air and missile strikes, Hardie told The Post.

“The Patriot is Ukraine’s most capable surface-to-air missile system and is one of its only systems that can reliably intercept ballistic missiles,” he said. “It’s good to see the United States, along with Germany and the Netherlands, pledging more Patriots for Kyiv. But Ukraine will still need more.”

Zelensky has been pleading for more of the systems — which Washington also uses to protect the White House — since the war’s early months. The US sent its first Patriot to Ukraine in December 2022.

During a summit held to mark the war’s second anniversary in February, Zelensky said his country needed seven more Patriots to effectively protect Ukraine’s airspace and keep his people safe from Moscow’s frequent strikes on civilian targets such as apartment buildings, hospitals and schools.

While more Patriots are needed, they would not necessarily need to come from the Pentagon’s limited stockpile, as several other nations — including Spain, Greece, Poland, Sweden, Japan and South Korea — also have the systems.

“One potential source is Israel, which is mothballing its eight Patriot batteries,” Hardie said. “Washington should try to convince the Israelis to transfer their Patriots to the United States, which should then donate them to Ukraine.”

Austin has also encouraged other partner nations to donate Patriots at previous UDCG meetings. The group, which Austin launched two years ago, is made up of roughly 50 nations that meet monthly to coordinate military assistance to Kyiv.

“There are countries that have Patriots, and so what we’re doing is continuing to engage those countries,” he told the House Armed Services Committee in April. “I have talked to the leaders of several countries … myself here in the last two weeks, encouraging them to give up more capability or provide more capability.”