Sen. Hillary Rodham Clinton is weighing in on who she thinks should be the next police chief of Fairfax County, throwing her support to a Secret Service executive who helped protect her and the former president.

The Democratic senator from New York has sent a letter on behalf of Donald A. Flynn to the chairman of the Fairfax Board of Supervisors, which could make a decision by Monday.

Flynn, 52, is a former Fairfax police officer who joined the Secret Service in 1981 and is now an assistant director in charge of the Office of Inspection. He is competing against four Fairfax commanders for the chief's job, and is scheduled to be interviewed by the board Monday.

Clinton wrote that Flynn was assigned to her Secret Service detail in July 1992, during her husband's first presidential campaign. He later served as director of the first lady's security detail and then as head of the president's detail. Flynn also coordinated protection for Clinton when she entered the Senate in 2001 and accompanied her last year on trips to Afghanistan and Iraq.

"Should you select Don for this important assignment," Clinton wrote, "I believe that Fairfax County will be as well served as my family and I were during our time at the White House. I recommend him highly."

The letter was faxed Wednesday to board Chairman Gerald E. Connolly (D). Clinton told Connolly he could share the letter with other members of the 10-person board, and Connolly said yesterday that he will do that.

"We always welcome firsthand references from any first family," Connolly said. "We're honored to receive it and certainly will take it into consideration in our deliberations."

The senator's office declined to comment yesterday on the letter. Calls placed to the Secret Service last night to reach Flynn were not returned.

Lt. Col. Suzanne G. Devlin, 50, who also is seeking the job, has been acting chief since the retirement of J. Thomas Manger in January. She would be the department's first female chief.

No outside candidate has been selected to head the Fairfax police department in its 64-year history, though Flynn's supporters point out that he spent eight years as a well-regarded officer and detective in Fairfax at the beginning of his career. A retired deputy chief, Michael W. Young, was selected for the job in 1992 and served for three years.

Flynn also has the backing of the 600-member Fairfax police union. In a letter to its members posted on its Web site, the executive board of the Fairfax Coalition of Police Local 5000 said Flynn "is not an 'outsider' as he has been labeled. He started his career here and wants to return with a passion to bring all that he has learned over the years." The union noted that Flynn worked as "a high level administrator for an agency five times the size of the Fairfax County police."

Flynn faces competition from police commanders who are more familiar to the board.

Devlin has been on the force for 28 years. Lt. Col. David M. Rohrer, 47, head of investigations and operations, is a 23-year veteran. Lt. Col. Charles K. Peters, 44, head of patrol, is a 22-year veteran. Maj. Tyrone R. Morrow, 40, a patrol commander, is a 20-year veteran. All four have experience meeting with supervisors as either station commanders or department executives.

A sixth candidate, Assistant Chief Alfred J. Broadbent of the D.C. police, withdrew as a finalist this week after accepting a job as head of security for Amtrak.

Initially, only the four in-house candidates were named finalists by County Executive Anthony H. Griffin. But after the police union protested that Flynn had not been granted an interview with a selection panel created by Griffin -- because Flynn had never been a major in a large police department -- the panel was reconvened and Flynn was interviewed.

A majority of the panel still did not favor Flynn, but the Board of Supervisors decided before Broadbent dropped out that it would interview him and Flynn on Monday.

Clinton's letter said Flynn's "diplomatic and people skills ensured the cooperation of law enforcement and security forces throughout this country, and in foreign visits from Beijing to Senegal, and many places in between."

"Certainly Senator Clinton thinks very highly of Mr. Flynn, and that's to his credit," Connolly said. "I think the board's going to look at the merits of all the candidates. We've been impressed with the other candidates."