LONDON — China’s performance at the recent G-20 summit meeting once again showed its skill at running diplomatic rings around Europe. Its audacious eve-of-summit call for a new global reserve currency to replace the dollar, the plaudits it won for a modest contribution to the International Monetary Fund, and President Hu Jintao’s occupancy of the center-stage in the leaders’ photo-call — added up to a great public relations triumph.

But while China edges toward the top-table, Europe’s leaders remain disunited and unsure of how to deal with the rising giant.

As European capitals prepare for the E.U.-China summit next month — rescheduled from last autumn after China canceled the meeting in retaliation for President Nicolas Sarkozy’s visit with the...