WASHINGTON — President Vladimir V. Putin warned President Biden on Thursday that any economic sanctions imposed on Russia if it were to take new military action against Ukraine would result in a “complete rupture” of relations between the two nuclear superpowers, a Russian official told reporters on Thursday evening.

A 50-minute phone call that Mr. Putin requested, and which both sides described as businesslike, ended without clarity about Mr. Putin’s intentions. He has massed 100,000 or so troops on the border with Ukraine, and issued demands for the North Atlantic Treaty Organization and the United States to pull back their forces in the region, but apparently has not decided whether to order an invasion.

Mr. Biden, for his part, “made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine,” according to a terse White House account of the call.

American officials declined to discuss any of the substance of the discussion, insisting that, unlike the Russians, they would not negotiate in public. But both sides appeared to be trying to shape the diplomatic landscape for talks that will begin in Geneva on Jan. 10, and then move to Brussels and Vienna later in the week in sessions that will include NATO allies and then Ukraine itself.

In Moscow, Yuri V. Ushakov, Mr. Putin’s foreign policy adviser, said the Russian president had conveyed Moscow’s expectation that the upcoming talks would lead to “legally formulated guarantees of security” for Russia. He added that the conversation had created a “positive background” for negotiations in January, but that no compromises had been reached.

The conversation on Thursday appeared to be part of the maneuvering for advantage as the first talks approach. Mr. Ushakov said Mr. Putin warned that harsh sanctions would be a mistake, and that, as Mr. Ushakov put it, “in this situation, it’s better not to make such mistakes.” But he also said that Mr. Biden had observed more than once during the call that “it’s impossible to win” a nuclear war — something Mr. Biden has often said in public.

While the tone of the call was constructive, according to the Kremlin aide, Mr. Putin repeated his claims that Russia felt threatened by an encroaching NATO. He said that Russia would “conduct itself as the United States would behave if offensive weapons were near the United States.”

The Biden administration, like the Trump administration before it, has provided hundreds of millions of dollars in aid to the Ukrainian military to fund what it characterizes as purely defensive arms, including anti-tank missiles to repel a threatened Russian invasion. Russia has called those offensive weapons that threaten its own forces.

An American official, briefing reporters on the condition of anonymity, said the call “set the sort of tone and tenor for the diplomatic engagements” to come in January. But he declined to “get into the territory of starting to negotiate in public,” saying that “whatever the Russian side has decided is its best tactic and strategy in terms of its public pronouncements, we really believed, based on past precedents, that it is most constructive to have these conversations privately.”

Mr. Biden and Mr. Putin had radically different objectives going into the call. By massing troops on the border and then publishing two draft treaties that had echoes of Cold War-era demands, Mr. Putin created an international crisis and made plain his desire to wind back the clock 30 years, to just before the collapse of the Soviet Union. He demanded that Ukraine halt its embrace of the West, that the United States and its allies halt all military activity in Eastern Europe and Central Asia and that NATO freeze its expansion to the east and roll back military deployments near Russia’s borders.

In Washington and European capitals, most of the proposed treaty language was immediately rejected as an effort to redraw the post-Cold War boundaries of Europe, and, with the threat of invasion, force Ukraine back into Moscow’s orbit.

Yet despite Russia’s damaged economy and diminished capabilities, Mr. Putin is dealing from a strong hand: He demonstrated in 2014, with the annexation of Crimea, his willingness to pick off Russian-speaking territory. And he is confident that the United States and its NATO allies will not commit forces to the task of pushing back.

But all that was true when the two leaders last spoke on Dec. 3. So they entered the second conversation on Thursday amid speculation that the Russian leader was feeling out Mr. Biden’s red lines ahead of the formal round of talks next month.

A senior administration official told reporters on Wednesday that the United States assessment was that Mr. Putin had not decided whether to invade Ukraine. But the Biden administration expected that Russia would have to make that decision in the next month, in the brief window ahead of the spring thaw in March or April that would make it difficult to roll heavy equipment into Ukraine.

Russia’s foreign minister, Sergey V. Lavrov, had aired concerns ahead of Thursday’s call that the United States might choose a tactic of dragging out the talks for as long as possible, tying up diplomats in endless meetings even as it expressed willingness to engage. The U.S. has suggested a return to a lengthy diplomatic process.

But Mr. Lavrov said on Monday that Russia should not be left in a situation where “our proposals are tied up in endless discussions, which the West is famous for and which it knows how to do.” It is important, he said, that, “there is a result of all these diplomatic efforts.”

He said the Russian government remained skeptical that the United States and NATO would truly engage on Mr. Putin’s demands. “We have serious doubts that the key thing in the proposals — the unconditional demand for a halt to NATO’s eastward expansion — won’t fall by the wayside,” he said in the comments, carried by the Tass news agency.

Russia’s demands are so sweeping that many political analysts view them as untenable, signifying either a bargaining chip for Russia or a justification for war when its demands are inevitably rejected. NATO immediately dismissed the central stipulation to guarantee a halt to admitting new members.

While the demands are addressed to the United States and NATO, Russia’s military threat is aimed at Ukraine. The United States has said Russia has amassed tens of thousands of troops near Ukraine’s borders, and that despite calls for “de-escalation,” the Russians have shown no signs of leaving and have instead inflamed the situation.

Still, American officials believe that Mr. Putin has not yet decided to order the invasion — and may still be convinced to back off. So they have made public their plans for extreme economic sanctions if an invasion starts, while signaling they are open to diplomacy.

“A broader challenge of the crisis is Russia pointing a gun at Ukraine’s head while asking the West to make concessions,” said Samuel Charap, a Russian security analyst at the RAND Corporation. “And that has been the dynamic here.”

Ukrainian officials have been quietly searching for diplomatic openings of their own. The government in Kyiv has been exploring whether negotiations for cease-fires and related security matters in the long-simmering conflict with Russian-backed separatists in eastern Ukraine can dial down the wider tensions, according to a senior U.S. official who briefed journalists in Washington before the presidential phone call.

“We have had very good discussions with the Ukrainian side in terms of short-term confidence-building measures they have put on the table with the Russian side,” the official said, speaking without attribution under terms set by the Biden White House. “For there to be real progress in these talks for us to get to a place where we have security and stability in Europe, a context of de-escalation rather than escalation will be required.”

In an early sign of success of the Ukrainian initiative, the Organization for Security and Cooperation in Europe brokered a holiday cease-fire along the front that held for several days, though skirmishing along the eastern Ukrainian trench line resumed recently. Discussions are underway for other such gestures, including an exchange of prisoners between Ukraine and Russian-backed separatists.

At the same time, Jake Sullivan, Mr. Biden’s national security adviser, said in a talk at the Council on Foreign Relations that the flow of arms to Ukraine would continue, raising the potential cost of an invasion and occupation. In conversations with his Russian counterpart, Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, has made clear that while Russia might succeed in taking over parts of Ukraine, it would pay a huge human cost in trying to occupy it.

Mr. Putin, for his part, has made it known that he sees providing arms to Ukraine as a threat to Russia and that it must stop.

“The administration’s in a tight spot,” Mr. Charap said. “The Ukrainians are clearly making a lot of requests, and they have a lot of sympathetic ears on the Hill and more broadly in Washington. And there’s the question, if this is imminent, and there’s anything you can do to help, now is the time. On the other hand, we are asking Russia to de-escalate, and they would see this as escalatory.”