* Big San Francisco bank serving Chinese community closed

* UCB, bought by East West, is 120th U.S. failure this year

* Beijing says China operations of closed bank are sound (Adds Chinese regulator, Minsheng background in paras 8-12)

WASHINGTON, Nov 6 (Reuters) - United Commercial Bank, a big San Francisco bank with branches in China, was closed by state regulators on Friday and its banking operations were acquired by East West Bancorp Inc, also active in both nations.

East West (EWBC.O: Quote, Profile, Research) said the transaction made it the second-largest independent bank in California. Based in Pasadena, East West has 137 U.S. branches, including offices in New York, Atlanta, Boston and Seattle, and four in China.

United Commercial Bank, with assets of $11.2 billion, was the 120th U.S. bank to fail this year. Regulators closed four other banks on Friday, in Georgia, Michigan, Missouri and Minnesota. Failures already were the highest since 1992.

Banks are struggling to clean up their balance sheets as loans made during the credit boom continue to deteriorate. The FDIC has said the pace of failures will remain elevated through next year.

Last year 25 institutions were closed by regulators, compared to three in all of 2007.

Dominic Ng, chief executive of East West Bank, said the transaction was "a transformational event" that strengthened his bank's position. East West's assets increased to $19 billion, from $12.5 billion.