The largest single addition to the District's police department -- 324 men and 122 women -- yesterday officially joined a force dramatically altered by a year-long recruitment drive.

In many ways, yesterday's graduating class represents a success story for the department, which has trained more than 1,000 cadets since October 1989 in an antiquated academy so small it required double shifts.

Now, with rookies making up more than 20 percent of the 4,687-member force, police officials acknowledge that the very face of the department has changed. The emphasis, and the challenge for the future, is making sure that the new graduates receive proper on-the-job training, a critical component of an officer's education.

In the last year, that has not always been easy. The sheer number of new officers means that the mentor, in some instances, is not much older than the rookie, said Lt. Reginald Smith, a police spokesman.

As a result, there has been grumbling by some veterans who question the training and discipline of new officers. But Smith said this is no different from 20 years ago, when the department had a three-year expansion that raised the number of officers to an all-time high of 5,100.

"I'd like to think that we're becoming more bilingual, we have more college graduates," said Smith, who was part of the hiring boom in the late 1960s. "Some of us are too critical of these kids, but they're bright and they've made a serious commitment."

The payoff, said Smith, will be in two to three years, when the rookies complete their street training. By then, they will have walked beats, driven patrol cars, handled sufficient cases and learned the court system.

Yesterday's graduates, sworn in during a ceremony at the University of the District of Columbia, included 324 blacks, 110 whites, 2 Asians and 10 classified as "other." A number of rookies are Hispanic, but the department did not provide a precise breakdown.

Over the last 30 years, the city has emphasized the hiring of minorities, and the racial makeup of the department now reflects that of the District.

There are more than 900 women, over 20 percent of the force. As part of its effort to recruit qualified candidates, the department raised the age limit for new officers from 30 to 35. The average age of a police officer, as of May, was 37.

Two years ago, and in response to the growing drug-related violence, the D.C. Council authorized the hiring of 500 officers. Congress provided money for an additional 700. When the hiring is completed next year, the department will have 5,055 officers.

Since Oct. 1989, the department has added 1,067 officers. At the same time, 374 officers have retired, so the net gain is 693, slightly more than half the number for which funding has been received.

The outflow of officers will continue in the next two years, as those hired during the drive 20 years ago begin retiring. An incentive to keep officers an extra year, which gave them a 5 percent raise for the 21st year of service, expired with the contract in August.

Recruiters have promoted the department in states along the eastern seaboard, trying to attract applicants. The department developed two pools of prospective officers, one for candidates 21 and over and a second for high school students who join as civilian cadets.