Three of the 178 D.C. police recruits hired in December under congressional pressure to bolster the city's police force are being fired for falsifying their job applications to conceal arrest records.

The three recruits, who were among one of the largest groups of new appointees to enter training for the police department in the last decade, have all been served 30-day notices of their impending dismissals and placed on administrative leave.

Police Chief Maurice T. Turner said yesterday the three recruits should not have been hired and blamed the error on one of several investigators charged with conducting background checks on applicants during a massive screening last fall.

The investigator, who had been attached to the recruiting office to assist in efforts to augment the police force, has since been reassigned, Turner said. He declined to name the officer.

There were conflicting explanations among police officials on how the cadets came to be hired. Some suggested that a deadline created by Turner for hiring the additional officers had made a mistake inevitable. Turner said the fault was "human error, not a system error."

"One of the investigators was derelict in his duty," Turner said. "It had nothing to do with time."

Records revealed that all three recruits had been arrested within the past three years for minor crimes, ranging from petty larceny to possession of marijuana to shoplifting, authorities said. Police officials declined to name the recruits, and said that none had been convicted of the crimes for which they had been arrested, but all had failed to disclose the arrests in their applications.

All three have appealed their dismissal to Assistant Chief Theodore R. Carr, head of police administration.

The current class of recruits was formed amid a swirl of public controversy. Since December 1980, Mayor Marion Barry had been under a congressional directive to hire at least 200 new officers to combat crime in the city. Until last July, when House members held up financial transfers among city agencies over the matter, Barry had not used $6 million that Congress had allocated for increased street patrols.

In August Barry, judging the police entrance examination to be discriminatory against blacks, proposed to select new recruits by lottery. The House voted down that proposal in September. Barry promised to hire the new officers by February and Turner set a Dec. 14 deadline for appointing new applicants. Most of the current class of recruits, including the three facing dismissal, were hired on that date.

Reports of the three cadets' impending dismissals have circulated for weeks in the police department. Two weeks ago top officials involved in hiring and training new recruits denied that any cadets were about to be removed, but Tuesday Assistant Chief Carr acknowledged the dismissals.

Carr said normal procedures for background checks of new appointees had been abbreviated in order to accelerate the hiring process. Falsified statements on the job applications were discovered when personnel investigators received FBI reports of the recruits' arrest records, about two weeks after they had been hired. Normally, recruits are not hired until the FBI reports have been received.

Officials familiar with police hiring said the FBI checks had been forgone in the past, but could recall no recent instances when such a change in procedure had resulted in a recruit being fired.

In the late 1960s and early 1970s, president Richard M. Nixon ordered the D.C. police force strengthened to an unprecedented level of 5,100 officers. Following the massive hirings of that era, officials said, dozens of new officers were found to have arrest records and were dismissed.

D.C. police officials pride themselves on what they say is one of the toughest screening processes in the country. After passing written and physical examinations, applicants must complete a personal history form nearly 30 pages long. Many are immediately disqualified. Those remaining must survive the results of additional inquiries sent to city, county and state law enforcement agencies around the country and, eventually, the FBI.

Police Capt. Donald H. Christian, head of personnel, said he was unable to explain how the FBI discovered arrest records where his investigators had found none. The record requests from both agencies, he said, were sent to the same D.C. police records office.

He said he has reviewed the files of the rest of the recruits and found no problems there.

He would not, he said, hire future applicants without the FBI reports.