The NBA and AEG will announce today plans to design and operate at least a dozen arenas in China, extending the league’s presence in its largest foreign market. The arenas could form the infrastructure of an NBA-branded league in China.

Under their plan, the league and AEG will make modest cash investments in the arenas, but their expertise will give them substantial ownership stakes in the buildings.

The arenas are to be financed largely by local and provincial governments.

“We won’t do this without an economic return over time for AEG and the NBA,” said Timothy J. Leiweke, the president and chief executive of AEG.

He and David Stern, the NBA commissioner, will announce the joint venture before the Nets-Heat exhibition game at the O2 arena in London.

Stern said the league was looking to capitalize on a growing urban Chinese middle class with increasing disposal income.

“China is an enormous market with enormous potential, not only for basketball but for entertainment venues,” he said in an interview.

The league and AEG are partners in the Beijing arena where basketball was played at the Summer Olympics in August. They are looking at building arenas in major cities like Shanghai, Guangzhou and Shenzhen. The arenas will be designed to accommodate a broad range of uses beyond basketball.

“We see these venues as homes for basketball teams, hopefully, in a league that is a partnership between the NBA and the China Basketball Association,” Stern said.

The arenas are envisioned as 19,000-seat facilities, some extravagant and some modest, that would be part of entertainment districts in some of the largest Chinese cities.

“Our issue is which 12 do we choose?” Leiweke said in an interview last week from Dubai. “I think we’ll have 30 or 40 of these opportunities, and 15 will make sense. Within a week, you’ll hear of some of the markets we’ll jump into.”