Friedrich Merz, the likely next chancellor of Germany, announced on Friday that he had cut a deal with the Green Party to allow extensive new government spending for defense, infrastructure and projects related to climate change, appearing to seal the votes for a stunning turnabout in German fiscal policy before he even takes office.

The deal, which Mr. Merz announced after days of negotiations, paves the way for a vote early next week to pass measures that are billed as a response to President Trump’s moves to pull back American security guarantees for Europe.

The measures would breach Germany’s hallowed limits on government borrowing, as they apply to military spending, and create new funds of borrowed money to improve dilapidated infrastructure and address climate change.

Mr. Merz called the agreement “a good result acceptable to all parties involved.”