But Mr. Biden also made clear that while he was seeking to force the Saudis to face up to the huge human toll of their intervention in Yemen, he was not leaving them alone to deal with a hostile Iran. He said he would continue sales of defensive weapons to Saudi Arabia that were designed to protect against missiles, drones and cyberattacks from Tehran.

“We’re going to continue to support and help Saudi Arabia defend its sovereignty and its territorial integrity and its people,” the president said. He said nothing about the possibilities of imposing sanctions on the crown prince for his involvement in the Khashoggi killing, though Mr. Biden’s director of national intelligence, Avril D. Haines, has said she plans to declassify intelligence about the killing.

In another reversal of Trump-era policy, Mr. Biden also announced he was “stopping any planned troop withdrawals from Germany,” halting Mr. Trump’s order to redeploy 12,000 troops stationed in Germany.

National security experts from both parties had called that order shortsighted, saying it was rooted in Mr. Trump’s dislike of Chancellor Angela Merkel and his determination to force NATO nations to pay more for their own defenses, no matter what the strategic costs to the United States.

But strategically, it is Mr. Biden’s warning to Moscow that may, over the long run, say more about the redirection of American foreign policy than the decision to limit Saudi Arabia’s ability to prosecute a regional war. He is the first president since the fall of the Soviet Union who has decided against trying a “reset” with Russia, instead announcing what amounts to a new strategy of deterrence, if not containment.

Mr. Biden hardened his vow to respond to Russian efforts to disrupt American democracy and to the SolarWinds hacking, a vast intrusion into American government and private networks whose dimensions are still a mystery. He said that in a call with Mr. Putin last week, he told the Russian leader “in a manner very different from my predecessor, that the days of the United States rolling over in the face of Russia’s aggressive actions — interfering with our elections, cyberattacks, poisoning its citizens — are over.”

Mr. Biden called on Moscow to release the imprisoned dissident Aleksei A. Navalny, adding, “We will not hesitate to raise the cost on Russia.” But he did not specify how he would accomplish that, and his options may be limited. While the president hinted at a response “in kind” to the cyberattack, that could set off a round of escalation that has many American officials concerned.