UPDATE 2-Biden's speech on Israel and Ukraine draws 20.3 million viewers -Nielsen

(Adds viewer numbers from previous Oval Office speech in paragraph 2, and audience numbers for the cable networks in paragraph 5,)

By Dawn Chmielewski and Danielle Broadway

Oct 20 (Reuters) - An estimated 20.3 million people watched U.S. President Joe Biden's Thursday night prime-time speech advocating wartime aid to support Israel and Ukraine, according to research firm Nielsen.

That is a bigger audience than Biden attracted in June, when he made a prime-time Oval Office speech to trumpet a bipartisan deal to end the debt limit crisis. That drew just 6.2 million viewers and was only picked up by two of the major U.S. broadcast networks, according to Nielsen.

Thursday's viewership numbers were tallied across 10 U.S. broadcast and cable networks, including ABC, CBS, CNN, Fox News and NBC.

Two-thirds of viewers watched Biden's 15-minute speech on broadcast networks, with 35% tuned in to a cable network. More than three-quarters of the TV audience was over the age of 55, according to Nielsen.

Fox News attracted the largest cable audience, with nearly 3.4 million viewers, surpassing rivals MSNBC, with an audience of 2.1 million viewers, and CNN with 1.4 million, according to Nielsen.

Biden sought to link Hamas militants in the Gaza Strip who attacked Israel to Russian President Vladimir Putin, whose forces invaded Ukraine in February 2022, and framed the conflicts as a threat to democracy.

"American leadership is what holds the world together. American alliances are what keep us, America, safe," said Biden.

Biden will ask Congress for $100 billion in new spending, including $60 billion for Ukraine and $14 billion for Israel, a source familiar with his plan told Reuters. (Reporting by Dawn Chmielewski, Danielle Broadway, Patricia Zengerle and Trevor Hunnicutt in Washington; Editing by Leslie Adler and Daniel Wallis)