NATO leaders, who are gathering at a summit meeting on Monday, have usually gone out of their way to adjust to the strategic priorities of the group’s most powerful member, the United States. But the issue of China is more problematic because NATO is a regional military alliance of Europe and North America. Its main concern remains a newly aggressive Russia — not distant China. China is expanding military exercises with Russia, sending its ships into the Mediterranean. It also has a base in Africa. So it has gotten NATO’s attention. But NATO member states from Central and Eastern Europe, as well as Germany, are concerned that a new concentration on China will divert alliance attention and resources from the problem closer to home.