President Biden will deliver a prime-time speech on Thursday about the war in Ukraine and the terror attacks in Israel as his administration prepares to call on Congress to approve tens of billions of dollars in military aid for the two embattled nations.

The address will mark the second time Mr. Biden has delivered formal remarks from the Oval Office since becoming president. In June, he spoke from behind the Resolute Desk about a bipartisan agreement to avoid defaulting on the nation’s debt, an agreement that Republicans in the House later abandoned.

In Thursday’s speech, Mr. Biden will address the American response to the two grave struggles that he has said threaten democratic stability across the globe: the war that followed Russia’s invasion of Ukraine last year and the one that started this month after the brutal assault by Hamas on Israel on Oct. 7.

A senior White House official said Mr. Biden will seek to present the American people a broadly framed explanation for why two wars half a world away are critical to the national security of the United States.

The official, who asked not to be identified in order to discuss planning for the president’s speech, said the purpose of the address is for the president to reflect on the events of recent weeks in Israel and the 600 days that Ukraine has been fighting since Russia’s invasion.

In a whirlwind visit to Israel on Tuesday, Mr. Biden said he would soon “ask the United States Congress for an unprecedented support package for Israel’s defense.” He said the request would help supply Israel’s Iron Dome air defense system with the ammunition it needs to protect Israelis from missiles.

The White House official said Mr. Biden was not expected to reveal specific details about the congressional funding request. The administration will provide more details on Friday, the official said.

Jake Sullivan, the president’s national security adviser, said this week that the request for aid to Israel would be made alongside another request for more military equipment for Ukraine, which has been struggling to take back territory that Russia seized in the 20 months since the war began.

“The president has made clear that he is going to go to Congress with a package of funding for Ukraine as well as continued support for Israel,” Mr. Sullivan said Sunday on CBS’s “Face the Nation” program.

The White House has provided few details about the scope of the aid that it will request for Israel and Ukraine. But multiple people familiar with the plan say Mr. Biden is expected to ask Congress in the coming days to approve about $100 billion in emergency funds to arm Israel, Ukraine and Taiwan and fortify the U.S.-Mexico border.

Thursday’s address could be a chance to draw Republicans and Democrats together behind support for both Israel and Ukraine, something that has traditionally had bipartisan support. Mr. Biden’s initial speech condemning Hamas following its attacks on Oct. 7 drew widespread praise from members of both parties in the United States.

But that bipartisanship may be tested when the president formally asks Congress for money to help finance the fighting. Some Republicans had already begun to question the need for ongoing American aid to Ukraine. And a small but vocal group of Democratic lawmakers fiercely oppose more aid to Israel.

The president will have to navigate a series of ideological differences if he seeks all of the aid in a single congressional vote. And as of Wednesday evening, House Republicans had still not chosen a speaker, leaving that chamber, and the entire Congress, in legislative limbo and without the power to act on any request that Mr. Biden makes.