In a move aimed at further diversifying its business, City National Bank announced last week that it would expand its wealth management operations with another acquisition.

City National Corp., the bank’s L.A.-based parent company, said it would acquire a majority interest in Lee Munder Capital Group by mid-July. The firm, based in Boston, manages assets for corporations, pensions, endowments and affluent households.

“Wealth management provides fee income, and most of the bank’s revenues today are generated by loans and interest spreads,” said Richard Gershen, City National’s vice president of wealth management. “Having a business that collects fees as opposed to earning money on interest-rate spreads is a diversifier giving us a source of revenue which, historically, has been more stable. Generally this has been a strategic priority for some time.”

The bank made a major expansion of its wealth management business in 2003 with the acquisition of Convergent Capital Management LLC, an asset management holding company based in Chicago. Last week’s announcement marks the latest in a series of smaller expansions since then.

Munder will be merged with Independence Investments, another City National-owned institutional asset management firm based in Boston that was acquired three years ago. The combined companies, with $4 billion under management, will operate under the name of Lee Munder Capital Group as an affiliate of Convergent LLC and will be the bank’s primary institutional asset management firm.

Ken Swan, Lee Munder’s president, said City National was a perfect fit for Munder, which was seeking to beef up its size.

“We were looking to have a strategic as well as financial partner,” said Swan, who will become the combined company’s chief executive in July. “This will provide us with some additional capital to take advantage of some of the opportunities in the market place of today.”

With the new acquisition, company officials said, about 20 percent of the City National’s gross revenues will come from asset management.

Analyst Christopher Nolan with Maxum Group called the acquisition a smart move, noting it would lessen the bank’s dependence on income based on short-term interest rates.

“It builds on their strength,” said Nolan.