Leaving combat operations in Afghanistan behind, NATO is shifting its focus to Europe in 2015 and the creation of its new ultra-rapid-reaction force, designed as a deterrent to Russia.

The priority for the 28-member alliance will be to get the new agile expeditionary force into operation, but also settling the question of who will pay for it, analysts say.

The multinational force, often called the "spearhead," was ordered into existence by President Obama and other NATO leaders in September so it could be deployed to reinforce alliance members feeling threatened by the actions or ambitions of Vladimir Putin's Russia.

NATO Secretary-General Jens Stoltenberg has called the new force and other components of the reboot of alliance capabilities "the biggest reinforcement of our collective defense since the end of the Cold War."

Stoltenberg, now in his third month as the alliance's top-ranking civilian official, said it is his "top priority to implement this plan in full and on time."

With NATO officially out of combat operations in Afghanistan as of Jan. 1, the alliance's agenda is expected to be dominated by the new strategic realities in Europe conjured up by Moscow's annexation of Crimea and alleged proxy war in eastern Ukraine, and what the West should do in response.

"NATO's biggest challenge in 2015 will be focusing on and advancing its core mission — ensuring the security of the alliance's members and promoting stability in Europe," said Michael Brown, dean of the Elliot School of International Affairs at George Washington University.

"This will be a challenge because the alliance's leaders have taken collective defense for granted for many years, because Russia has developed an array of unconventional tactics that will require new and unconventional responses, and because NATO will continue to be involved in training activities in Afghanistan," Brown said.

In reaction to Moscow's actions, Obama and the other NATO leaders approved a Readiness Action Plan to upgrade alliance capabilities, and 2015 "will be about making it more concrete and visible for Russia," said Marcin Terlikowski, head of the European Security and Defense Economics project at the Polish Institute of International Affairs in Warsaw.

"The main task will be to decide what this force will be, where it will be based, and how it will be commanded," Terlikowski said. "It's also about money."

It is unclear who will pay for the force, said Bruno Lete, senior program officer for foreign and security policy at the German Marshall Fund, a Brussels-based think tank.

Many are hoping the Americans will foot much of the bill, while others are looking to Germany, NATO's wealthiest and most populous member in Europe, Lete said.

It is vital for NATO cohesiveness that as many members as possible contribute to payments, he said, or "the plan will lose its legitimacy."

In 2015, decisions are also expected that would continue the rotation of U.S. and other allies' air, land and naval forces to maintain a non-stop heightened profile in the NATO member countries closest to Russia. On New Year's Day, NATO officials said, the Italian Air Force, flying four Eurofighter jets, took over from the Portuguese in executing one of those operations, the Baltic Air Policing mission in the skies over Estonia, Latvia and Lithuania.

In the coming year, the go-ahead should also be given by NATO governments to stockpile fuel, ammunition and other supplies and equipment in the frontline countries for use by the rapid reaction force if needed, Terlikowski and other analysts said.

To signal its resolve to come to defend its members in Eastern and Central Europe, NATO conducted more than 200 military exercises in 2014, and the member countries are expected to decide to maintain that pace.

"Russia has to see that NATO is resolved to defend its values," Terlikowski said. "And the core value of NATO is solidarity: attack one member, and the whole alliance, including the U.S., will respond."

Some parameters of what's been officially named the Very High Readiness Joint Task Force are already known. Stoltenberg has said the prototype to be formed in 2015 will have a ground component of several thousand troops largely contributed by Germany, Norway and the Netherlands.

Poland, NATO's most important member in the former Soviet bloc, expects to host some of the new force's command and control elements, including at the existing Multinational Corps Northeast headquarters in the western city of Szczecin.

For Stoltenberg, trying to coax alliance members in 2015 into spending more on defense in general will predictably be another core task. In September, the national leaders committed to spending 2 percent of gross domestic product on defense, but gave themselves 10 years to meet the target. For decades, Washington has complained that too many Europeans are not shouldering their fair share of the burden for trans-Atlantic security.