ESTELLE Richman, the state's secretary of public welfare, is leaving that job on Thursday to become the chief operating officer of the U.S. Department of Housing and Urban Development.

She will be missed. To put it mildly.

Richman first came to Philadelphia 20 years ago to oversee the closing of the state mental hospital at Byberry. In city positions as varied as health commissioner, director of social services and managing director, Richman's innovations and high standards won her a well-deserved national reputation.

While her accomplishments are too numerous to list, one that stands out for us is the creation in 1997 of the city's nonprofit-managed mental-health-care company - Community Behavioral Health Inc. - which transformed the delivery of mental-health services, and saved big bucks, too.

Richman is a one-woman testimonial to the power of government to make a positive difference in the lives of ordinary people.