Helene M. Cassell, a 12-year veteran of the Fairfax County police force, was promoted to captain yesterday, becoming the first woman to achieve that rank in her department and one of the highest ranking female law enforcement officers in the Washington area. Cassell, 38, will command the Fair Oaks substation in the Chantilly area of the county, which has a complement of 67 officers and 12 civilians.

Fairfax County Police Chief Carroll Buracker said Cassell "was selected based on her knowledge, skills and ability. Her sex had nothing to do with it." He said her promotion through the ranks "clearly shows this department's openness to minorities and women."

Described by colleagues as friendly, outspoken, intelligent and easy to work for, Cassell has a master's degree in business management in a department that does not require its officers even to have a bachelor's degree.

She has become something of an example for other women rising in the department, and it is not a role she minds. "I think I will be a role model for other women . . . . It probably will not be very long at all before women are progressing through the ranks."

Like most of those who achieve upper command ranks in the 800-officer department, Cassell has served at each of the ranks below captain. She was also the department's first female corporal, sergeant and lieutenant.

Cassell has only two female peers in area police departments.

Arlington has a female lieutenant who is in an equivalent command position, in charge of that jurisdiction's midnight shift of 45 officers.

And the District has a female inspector, who is currently serving as the department's equal employment opportunity officer, but had previously been the ranking officer on the midnight shift in the city.

Although there are no figures showing the prevalence of women in command ranks of police forces nationwide, promotion of women to those ranks "remains very slow", according to Peggy Triplett, a program analyst for the D.C. police department who did a study of women and minorities in police departments. She said it is still "very rare" for women to hold command positions in major departments.

Cassell, known by her colleagues as a forthright and respected supervisor, said she doesn't "feel like a crusader or a pioneer" and that after spending her years as a lieutenant in an administrative job at headquarters, it "feels great" to be headed back to hands-on police work. She assumes command on Saturday, and will be in charge of all management functions at the substation, from budget to directing criminal investigations.

Although Cassell's promotion makes her one of the top 27 people in the department, Fairfax County lags behind other area jurisdictions in overall hiring of women.

Just over 6 percent of the officers in Fairfax County are women.

In contrast, women make up 13 percent of the Arlington police force, 10 percent of the Montgomery County force and 9 percent of the Alexandria force. Of suburban jurisdictions, only Prince George's County has proportionately fewer women -- 5.8 percent of its force. District of Columbia police could not provide figures on how many female officers they have.

Cassell's husband Rick Cassell is a Secret Service agent assigned to Vice President Bush, and the couple last year adopted an orphaned Salvadoran boy who is now 6.

Also promoted were John E. Granfield, 40, to lieutenant colonel in the new position of deputy chief for operations; Michael Young and John Rob from the rank of captain to major, and Luther Nossett Jr. from first lieutenant to captain.