Fairfax County supervisors interviewed four internal candidates for chief of police yesterday, then postponed the process for three weeks to interview two candidates from outside the department who had not been finalists.

On July 12, the board plans to interview Donald A. Flynn, an assistant director of the U.S. Secret Service, and Alfred J. Broadbent, an assistant chief of the D.C. police, Fairfax sources said. The selection of a new chief may occur that day, sources familiar with the selection process said.

"The process is open," Board Chairman Gerald E. Connolly (D) said, emerging from three hours of interviews behind closed doors. No favorite has emerged for the job, now held by the acting chief, Lt. Col. Suzanne G. Devlin.

"We're impressed with the caliber of all the candidates we've interviewed so far," Connolly said.

Devlin, Lt. Col. Charles K. Peters, Lt. Col. David M. Rohrer and Maj. Tyrone R. Morrow met separately with the board for 40-minute interviews, where they were asked their ideas on traffic, police management issues and stopping gang violence, county board sources said.

Those four candidates were winnowed from nine applicants interviewed by a 17-member panel led by County Executive Anthony H. Griffin. The new chief will succeed J. Thomas Manger, who retired in January to take the top job in Montgomery County.

Griffin reduced a field of about 50 applicants, and last month his top nine candidates were interviewed by a screening panel of law enforcement officials, private citizens and county staff members. Only two of the nine candidates were from outside the Fairfax department, and one of them was Broadbent. Flynn was excluded because he did not meet the criterion of having served as a major or higher in a large police department. Flynn was an officer and detective in Fairfax for eight years before moving to the Secret Service.

Griffin initially submitted the four internal candidates to the board, without Broadbent or Flynn. But members of the county's police union lobbied county supervisors on Flynn's behalf, and those supervisors spoke to Griffin. So Griffin reconvened the panel last week to interview Flynn. The panel did not vote to support Flynn, but the board decided yesterday to interview Flynn and Broadbent anyway.

Flynn heads the Secret Service's Office of Inspection. He previously has overseen White House security and the presidential protective division. He left the Fairfax police in 1981 to join the service.

Broadbent, a 25-year veteran of the District police, leads the department's support services command, which has about 1,000 employees. Broadbent said yesterday that he had interviewed for the job but was recently told he was not a finalist.

Among the internal candidates, Devlin, Peters and Rohrer are the deputy chiefs who oversee the department's three main branches: Devlin handles administration, in addition to being acting chief; Peters directs patrol; and Rohrer commands investigations and operations. Morrow oversees three patrol stations within the patrol branch.

Staff writer Del Quentin Wilber contributed to this report.