Washington area police departments that expanded during the civil unrest of the 1970s are facing an early 1990s exodus of officers who are retiring after 20 years of service.

While the problem in suburban departments is moderate compared with that faced by the District -- where a wave of retirements over the next few years could impede law enforcement, sources say -- the rumblings about expected departures are being heard in Arlington, Prince George's and elsewhere.

"We have officers who are getting 20 years on and we hear undercurrent about their leaving," said Cpl. Wendy Maris, who recruits for the 250-officer police force in Alexandria. "Over the next three years there will be a turnover in personnel."

None of the departments has arrived at the specific number of officers it expects to lose when the 1970s recruits retire under policies that allow them to collect pensions after 20 years on the job. But both the carrot and the stick approaches are being used to deter retirements.

In Prince George's County, officers who stay beyond 20 years get a bonus of $1,000 for each additional year they work, up to five years.

Taking steps to make retirement less attractive, the Arlington County Board recently approved changes in health benefits for retiring county employees, linking coverage to length of service.

Under the new plan, effective next Jan. 1, full medical coverage will be available only to employees who have worked for the county for at least 25 years, rather than the current 20 years.

"It doesn't make sense, in an era when we're going to see fewer and fewer young people entering the work force, to maintain retirement packages that encourage people to retire early," said County Board Chairman Albert C. Eisenberg.

But area police departments, expecting significant numbers of 20-year veterans to retire nevertheless, plan to work harder to attract recruits and hold on to younger officers.

Almost all local departments say they have a problem with recruits who leave to work in state or federal law enforcement, where salaries are higher and the work is considered more glamorous.

"We all lose a lot of our officers to {the Bureau of} Alcohol, Tobacco and Firearms {and} DEA," said Maj. Edward Stevens of the Fairfax County police, referring to the federal Drug Enforcement Administration. "We're in close proximity to Washington, and no municipality can compete with the federal government."

Local police departments also face growing difficulty in attracting qualified recruits. For the first time in recent memory, for example, several slots allotted to Arlington County at the regional police academy went unfilled this spring.

A spokesman said five qualified applicants -- instead of the usual dozen -- were sent to the 10-week training session. Arlington could not fill the rest of its allocation, even though the department's starting salary of $30,000 per year is the highest of any local police force.

Other localities cite a declining interest in police work, low unemployment and a smaller pool of potential applicants as reasons they lack sufficient recruits. Increasing competition among departments is another reason.

"Everybody's looking for the same person: a good moral applicant with a solid work history, good edcuational background and no drug use," said Officer Sandy Exum, a recruiter for the Prince William Police Department.

As departments compete for recruits from the same shrinking pool, their tactics have become more aggressive.

"Every so often Fairfax conducts the recruiting equivalent of a fire sale," Eisenberg said. "They improve their benefits and get a lot of applicants going over there at one time, which makes things very competitive for Arlington."

Many jurisdictions have aggressive marketing campaigns stressing their strengths.

"We're trying to emphasize that we're the largest local law enforcement agency in the state," said Stevens of the Fairfax department, which has nearly 1,000 officers.

Exum said Prince William stresses that it is a newer police force in which an officer doesn't have to wait for someone to retire in order to be promoted.

Officials in Loudoun County say they have traveled to Pennsylvania and Delaware to find recruits at job fairs. Fairfax police say they have expanded their search to a 250-mile radius, taking in Long Island, Philadelphia and North Carolina.

Among the more aggressive is Prince George's County's recruiting program. The county, now with a police force of 1,200, hopes to expand to 1,400 by next July, said Col. Theodore Carr, chief of the department's bureau of administration.

"Every officer gets a cruiser for the job that he can take home and use 24 hours a day," Carr said. "We also pay a new recruit who stays with us for four years $1,000 for every year of college that he has, and we'll pay their moving expenses up to $750."