The US should send Ukraine all the weapons it asks for as Russia’s invasion reaches a pivotal moment that could change the outcome of the war, some policy analysts and lawmakers said Friday.

Ukrainians have mounted a fiercer resistance to Russian President Vladimir Putin’s invading forces than expected — and the West could sway the war decisively in Ukraine’s favor by supplying its fighters with heavy-duty weapons now, according to experts.

But to help Ukraine to prevail, the US must take the lead over its NATO allies, due to its global stature and massive military resources, said Dalibor Rohac, senior fellow at the American Enterprise Institute in Washington, DC.

“In the short term, if you want Ukrainians to win this war there is nobody like the United States that could make that happen,” Rohac told The Post.

“My main message is just do more,” Rohac said. “Send Ukrainians everything that they ask for, don’t be afraid of Putin, and he can actually lose this war.”

NATO pledged to send more weapons to aid in the conflict Thursday, amid growing reports of Russian brutality and atrocities against civilians in Ukraine.

US Secretary of State Antony Blinken said images and accounts of the tactics of the invading force has the Biden administration “looking across the board right now not only at what we provided, and what we continue to provide, but whether there are additional systems that could make a difference.”

There remains a reluctance by some NATO countries, however, to supply weapons that will be viewed as offensive as opposed to defensive. Other concerns have been raised about arming Ukrainians with modern high-tech weapons they haven’t been properly trained to use.

Retired Gen. Wesley Clark wrote in an op/ed published in The Post Friday that there is little time to waste to give Ukrainian forces hundreds of thousands of artillery rounds, tanks and MiGs and Sukhoi aircraft.

“Why? Because there is a window of opportunity now – for a week or two perhaps – in which Ukraine can counterattack in the north, south and east to expel Russian forces. This will require mobile armored forces and air power,” Clark wrote. “And if this window is lost, the future is darker and more uncertain.”

A Ukrainian victory could push Russia out of the country for good, putting Putin on his heels and forcing him to think twice about further conflicts in Georgia, Moldova and elsewhere, Clark said.

Russia’s failure in Ukraine would also give pause to China if it decides to launch new military conflicts over its borders, he wrote in the piece.

There is a crucial window in the next several weeks, military and policy experts said.

Russia is refocusing its attacks in the east of Ukraine, in the Donbas region, after having difficulties in some northern cities — and there are fears that the intensity of the coming offensive may turn the tide back in Moscow’s favor.

But even if the offensive sputters, Putin may agree to a ceasefire by mid-May, with a concession such as annexing a piece of the Donbas region that would allow him to call the operation a success, Rohac told The Post.

The Biden administration built its initial policies about supplying weapons under the assumption that Ukraine would be largely overcome, and the resistance would be mostly guerilla-style fighters in occupied land, he added. But the US needs to adapt now the overview of the war has changed.

“Ukrainians have a decent chance of actually chasing Russians out of Ukraine altogether and that, to us, would be would a priority to get that outcome.”

Senate Minority Leader Mitch McConnell (R-Ky.) said Biden “has been a little too cautious” about Ukraine.

“We need to give the Ukrainians everything they want,” he said in an interview on Fox News Friday. “They’ve demonstrated they have the will to fight, the ability to fight and our goal ought to be to win.”

McConnell said there was “no question” there were war crimes being committed by Putin’s forces — as he called for more than just talk from the US.

“Of course, Putin is not going to be deterred by being called a war criminal,” McConnell said. “He will be deterred on the battlefield … And so what we need to do is give (Ukrainians) every single useful weapon they ask for and need to beat the Russians.”

With Post wires