SIMI VALLEY, California — Secretary Austin on Saturday denounced those who advocate “an American retreat from responsibility” and said sustained American leadership is needed to help keep the world as safe, free and prosperous as possible. He also urged Congress to end the partisan gridlock that has stalled the federal budget and war spending.

The United States must reject calls to turn away from global interests and become more isolationist, he told an audience of lawmakers, corporate and defense leaders and government officials attending a security conference. Those who “try to pull up the drawbridge,” he said, undermine the security that has led to decades of prosperity.

In his remarks at the Reagan National Defense Forum in California’s Simi Valley, Austin delivered a lengthy defense of American support to Israel in its war against Hamas and to Ukraine in its struggle to battle Russia’s invasion. He said “the world will only become more dangerous if tyrants and terrorists believe that they can get away with wholesale aggression and mass slaughter.”

Mr. Austin met privately with top lawmakers on the House and Senate Armed Services Committees. His message of rejecting isolationism appeared directed at conservative lawmakers who are increasingly opposed to spending on overseas wars and back President Trump’s “America First’” ideology.

“You’ll hear some people try to brand an American retreat from responsibility as bold new leadership,” Mr. Austin said. “Make no mistake: It is not bold. It is not new. And it is not leadership.”

Congress has failed to approve any new money for the wars in Ukraine and Israel and has managed to pass only a short-term budget bill, known as a continuing resolution, that runs out early next year. The Senate has been deadlocked for months over one lawmaker’s move to block hundreds of military nominations, including critical senior commanders for key regions around the world.

“Our competitors don’t have to operate under continuing resolutions. And doing so erodes both our security and our ability to compete,” Austin said. He opened his speech with a plea to the lawmakers in the crowd to pass both the budget and the supplemental funding for the wars.

Administration officials have warned that money for Ukraine is running out and may only last through the end of this year. The Pentagon has about $5 billion worth of equipment it can send from its own stockpiles and has been eating away at that almost weekly. Money to replace military weapons and equipment taken from Pentagon stocks to send to Ukraine is rapidly dwindling, and totals about $1 billion.

Mr. Austin, who was in Ukraine’s capital less than two weeks ago, has repeatedly pressed the importance of helping Ukraine battle Russia’s invasion, as part of a broader campaign to prevent Russian President Vladimir Putin from threatening other countries in Europe.

Mr. Austin also noted that as much as $50 billion of that supplemental budget request for the wars would go through American defense companies, helping to create or support tens of thousands of jobs in 30 states.

While he did not mention it in his address, Mr. Austin has often criticized Congress for its failure to confirm more than 400 military officers nominated for promotions or other jobs. Senator Tuberville has blocked the nominations and objected when other senators have tried to get some through. On just two occasions has the Senate managed to vote to confirm a total of six high ranking leaders.

Almost 400 military nominations are in limbo, and the number is growing. Frustrated Republicans have tried unsuccessfully for almost nine months to quietly persuade Tuberville to drop the holds, and negotiations are continuing. Senior military officials have warned repeatedly that the situation threatens readiness and national security.

In other comments, Mr. Austin underscored the administration’s repeated insistence that Israel do more to protect civilians as it restarts its air assault against Hamas after a seven-day cease-fire to secure the release of prisoners.

Israeli fighter jets began hitting targets in the Gaza Strip minutes after the weeklong truce expired on Friday, and Israel dropped leaflets over parts of southern Gaza urging people to leave their homes, signaling it was preparing to widen its offensive. About 100 hostages were freed as part of the truce, but about 140 remain held by Hamas and others in Gaza.

While any country has a duty to respond to an attack like the October 7 assault by Hamas on Israel, Mr. Austin said, the lesson is that “you can only win in urban warfare by protecting civilians.” Mr. Austin said that if civilians are driven into the arms of the enemy by violence, it becomes a strategic defeat.