“If Europe does not take care of its own security, nobody else will do it for us,” said Jean-Claude Juncker, the president of the European Commission, the executive arm of the European Union. “A strong, competitive and innovative defense industrial base is what will give us strategic autonomy.”

Total military spending by European Union governments was about €200 billion last year, but the union does not currently have a budget for military research or procurement. The plan foresees a pilot phase of €90 million, or $95 million, up to 2020 — and €500 million, or $528 million, a year after that — for research into technologies like drones and for cybersecurity tools.

A second plank of the plan foresees spending 10 times that amount to help governments develop and buy hardware. But rather than drawing on the shared European Union budget, member states would make individual contributions, and some of the money might come from project-related bonds.

Obama administration officials welcomed the increased spending. “It is no secret that we’ve been asking them to do this for years,” said one senior administration official, speaking on the condition of anonymity to discuss alliance relations. But the official also said it was imperative that Mr. Trump reassured allies that his administration’s commitment to collective defense of NATO allies would be solid.

During his presidential campaign, Mr. Trump questioned whether the United States would automatically defend NATO allies if they were attacked, and said American support would depend on the willingness of those countries to pay their fair share for military protection. But since then, a number of Republican lawmakers and foreign policy experts — including those in close contact with Mr. Trump since he won the election — have insisted that the American commitment to NATO will remain strong.