The package includes $7 million for international relief organizations providing humanitarian aid to civilians impacted by the fighting between Kiev and pro-Russian separatists. Another $46 million will go to assist Ukrainian military and border guards.
Those efforts are in addition to $291 million in direct assistance the U.S. has already provided to Ukraine, as well as a $1 billion loan guarantee offered to stabilize its economy.
But the new assistance does not include lethal aid, which leaders in Kiev have long called for in their fight against pro-Russian separatists.
Poroshenko renewed that call during a joint address to Congress earlier Thursday, telling lawmakers "one cannot win a war with blankets."
"The security assurances that were extended to Ukraine then have failed to work, proving that no agreements or treaties can secure world order," he said. "Therefore, I urge you not to let Ukraine stand alone in the face of this aggression."
The Obama administration has so far resisted that demand, saying it would do little to end the crisis.
"The issue here is not whether the Ukrainian army has some additional weaponry," Obama said in August. "At least up until this point, they’ve been fighting a group of separatists who have engaged in some terrible violence but who can’t match the Ukrainian army."
The president did say that determination could change "if you start seeing an invasion by Russia."
"We’re not there yet," Obama said.
"What we have been doing is providing a whole host of assistance packages to the Ukrainian government and to their military,” he continued, “and we will continue to work with them to evaluate on a day-by-day, week-by-week basis what exactly they need in order to be able to defend their country and to deal with the separatist elements that currently are being armed by Russia."
The military assistance announced Thursday includes body armor, helmets, vehicles, night and thermal vision devices, heavy engineering equipment, advanced radios, patrol boats, rations, tents, counter-mortar radars and uniforms.
Obama’s meeting with Poroshenko takes place less than a week after the administration announced sweeping new sanctions targeting Russia's defense, finance and energy industries, including penalties on the country’s largest bank and many state-owned oil companies.
White House aides say the meeting is intended to send a strong message to Russian President Vladimir Putin.
"I think in this case maybe the picture of President Poroshenko sitting in the Oval Office will be worth at least a thousand words, both in English and in Russian," press secretary Josh Earnest said Wednesday.