An executive with a Falls Church-based managed-care company is District Mayor Anthony A. Williams's choice to take over the D.C. health department and try to reshape the city's troubled health care system, sources said yesterday.

Williams, in a news conference today, is to announce his selection of Ivan C.A. Walks, 42, to fill the health director's post, which has been vacant for 14 months as Williams (D) and his predecessor, Marion Barry, struggled to fill a position that is known within the nation's public health community for its instability.

The city has had five health directors since 1990, not counting interim leaders. For Williams, the lack of consistent leadership in the health department has forced the mayor to be the city's de facto health director. The empty post also has complicated Williams's efforts to improve an unbalanced health care system in which thousands of low-income residents lack access to basic care while hundreds of hospital beds remain unused.

D.C. health statistics, in many categories, rank the city well behind other major cities and the nation as a whole. They include life expectancy, infant mortality, maternal mortality, HIV and AIDS, teenage pregnancy, drug abuse and chronic diseases, and the number of residents with no health insurance.

Walks, a neuropsychiatrist with a background in health care administration, has been the vice president and associate national medical director for the past three years of ValueOptions Inc., sources said. While there, he has worked to design and implement a health care delivery system for the thousands of children in the District's foster care system.

The D.C. Council must vote on the mayor's choice. Sources say Walks will become acting head Sept. 13.