TOKYO — Japan will spend nearly $120 billion to stimulate its slowing economy and to help some of the areas worst affected by Typhoon Hagibis, Prime Minister Shinzo Abe announced on Thursday.

The new spending plan is aimed at addressing a slew of economic challenges facing Japan’s longtime leader, who has built his reputation on the country’s stronger growth after years of stagnation.

But the stimulus package, if passed, would continue Japan’s cycle of borrowing and spending to stoke growth and pay for the country’s expanding social welfare costs to support a rapidly aging population. The country already has the biggest debt load in the developed world relative to the size of its economy.

Mr. Abe’s administration has pledged to reverse the borrowing trend. Just two months ago the government raised the country’s consumption tax to help shore up the country’s finances, only to see retail sales slump.