The Biden administration announced on Tuesday that it was sending up to $300 million in weapons to Ukraine, the first new aid package for the country since funding ran out in late December.

The package, pulled together from money that Army accountants cobbled from savings from contracts that came in under bid, includes air defense interceptors, artillery rounds and armor systems, senior defense officials said. Two U.S. officials said the package also includes an older version of the Army’s longer-range missile systems known as ATACMS, which can travel 100 miles.

It is a stopgap measure at best, the officials said, but Ukraine is in dire need of air defense systems in particular, as Russia has continued its bombardment of towns particularly in the east.

The makeshift solution would keep advancing Russian troops at bay for only a few weeks, one official said.

Announcing the aid package at the White House, the national security adviser, Jake Sullivan, said that “Ukrainian troops have fought bravely, are fighting bravely throughout this war, but they are now forced to ration their ammunition under pressure on multiple fronts.”

He said the new package would “keep Ukraine’s guns firing for a period, but only a short period.” Mr. Sullivan called for Congress to pass a new Ukraine aid bill “as soon as possible.”