"If there is no U.S. support, it means that we have no air defence, no Patriot missiles, no jammers for electronic warfare, no 155-milimetre artillery rounds," Zelenskiy told the Washington Post.
"It means we will go back, retreat, step by step, in small steps," he said. "We are trying to find some way not to retreat."
Shortages of munitions, he said, meant "you have to do with less. How? Of course, to go back. Make the front line shorter. If it breaks, the Russians could go to the big cities."
Democratic President Joe Biden has urged the Republican-controlled U.S. House of Representatives to endorse the military and financial aid package, but House Speaker Mike Johnson has held up the matter for months, citing domestic priorities.
Zelenskiy told Johnson in a telephone conversation on Thursday that approval of the package was vital.
Russian forces captured the eastern town of Avdiivka last month and have made small gains since, but the front lines have changed little in months.
In his interview, the Ukrainian president said Ukraine was making up for shortages of missiles with home-produced weaponry and air defence systems, "but it is not enough".
More than two years into the war, Russia has intensified attacks on energy and other infrastructure in recent weeks. Ukrainian troops have been unable to advance, and Zelenskiy said Kyiv intended to pursue attacks on targets in Russia, including oil refineries.
He said Washington's reaction to the wave of Ukrainian attacks was "not positive", but Kyiv was using its own drones.
"We used our drones. Nobody can say to us you can't," he told the newspaper. If there is no air defence to protect our energy system and Russians attack it, my question is: Why can't we answer them?" he said.
"Their society has to learn to live without petrol, without diesel, without electricity. When Russia will stop these steps, we will stop."
(Reporting by Ron Popeski; Editing by Bill Berkrot and David Gregorio)
