The head of the Los Angeles County Museum of Art is resigning from her post, a move that comes on the heels of the museum’s announcement that it was moving forward with a big expansion after obtaining the needed funding.

In a decision announced Monday, Andrea L. Rich said she no longer had the energy to lead the museum after 10 years at the institution, but believed the museum was in far better shape now than when she was first appointed.

“LACMA has evolved with distinction during this last decade. Its future is bright,” said Rich, who will leave in November. “For a variety of reasons, I find myself no longer able to provide the energetic leadership LACMA requires to build upon the solid foundation that has been set in place during the past decade.”

Rich’s departure was unexpected, but it follows by less than a month an announcement by the museum that it had secured more than $150 million in donations and $150 million in bond financing for a major expansion and renovation project that is being designed by noted Italian architect Renzo Piano.

The museum is planning on building a new contemporary art center that is being financed with a $60 million donation by billionaire Eli Broad, along with a new Wilshire Avenue fa & #231;ade, entrance plaza and walkways in the first phase of the expansion project.

The project represented a major accomplishment for Rich, who saw another, more controversial renovation project that would have rebuilt nearly the entire complex fall flat in the face of donor indifference several years ago.

“The plans and funding are in place for the first phase of our expansion and upgrade, so the board and I agree that this is the opportune moment to set in motion the transition to new leadership,” Rich said.

Rich was praised by museum executives and board members.

“Andrea is a woman of extraordinary vision, intellect and capacity,” said LACMA board chairman Wally Weisman. “There is no other leader in the 40-year history of the museum that has left such a significant and indelible mark.”

Rich also was credited with expanding the museum’s already encyclopedic collections and improving its shaky bottom line by fattening up its endowment, which rose to $105 million in 2004 from $49 million in 1995.

Prior to her position at the museum, Rich was executive vice chancellor at UCLA. She was hired in June 1995 with executive responsibility for operations, including supervision of the director, who set the museum’s artistic direction. She was appointed director in 1999 when then-director Graham Beal resigned.

The museum has formed a search committee to find a replacement for Rich, who will continue to consult for LACMA after retiring.