The Smithsonian Institution's governing board on Monday said high-ranking executives at the museum complex will be barred from serving on corporate boards.

The board's decision followed Smithsonian Secretary Lawrence M. Small's resignation in March amid criticism about his spending. The board was acting on recommendations from a nearly three-month review by the Smithsonian Board of Regents' governance committee, which found that the board needed to increase transparency, among other things.

The committee took note that Marriott International Inc. had paid Small $208,000 in direct pay, stock and other compensation in 2006 for serving on its board. Small also served on the board of one of the Smithsonian's insurers, the Chubb Group, receiving $169,675 last year in cash and stock.

Deputy Secretary Sheila Burke has also sat on two corporate boards, including Chubb, which paid her nearly $194,676 last year in cash and stock. Burke resigned Monday, saying she believed the Smithsonian needed new leadership.

"To avoid even the appearance of conflict of interest ... Smithsonian senior executives shall not be permitted to serve on the board of a for-profit company," the committee wrote.

The committee also determined that the board should increase the number of business meetings each year from three to four and make its agenda and discussions more transparent.

The board pledged to meet regularly with the Smithsonian's top lawyer and chief financial officer, as well as its inspector general.

Many board members did not know critical details of Small's employment contract, and were unaware of tension between the Smithsonian museums and its central administration over the past seven years, the committee found.

"The Regents did not routinely receive, nor did they demand, the information necessary to support vigorous deliberation and well-reasoned decision-making," the committee wrote.

The report called for the creation of a Smithsonian Code of Ethics, a review of compensation systems for its federal and private trust fund employees and a public forum each year to emphasize the board's openness and "culture of accountability."

In addition, the board agreed to create a new position, chairman of the board, which will be separate from chancellor, a position typically held by the chief justice of the U.S. Supreme Court. The chancellor will continue to oversee meetings, but much of the oversight of the museum complex will be the chairman's responsibility.

The Smithsonian's 18 museums include the National Air and Space Museum, the National Museum of American History and the National Museum of Natural History. The National Zoo is also part of the Smithsonian, and a 19th museum devoted to black history is under development.

An internal audit in January found that Small had made $90,000 in unauthorized expenses since 2000, including private jet travel and expensive gifts. The audit also found that Small charged the Smithsonian more than $1.1 million for agreeing to use his mansion in Washington's affluent Woodley Park neighborhood for official functions.