A recently formed 85-member D.C. police task force whose assignment is to clear the streets of "career criminals" has arrested 24 persons during its first week of operation, including several people caught in the act of committing crimes, Police Chief Maurice T. Turner said yesterday.

However, most of the 24 were released on bail after their arrests, a fact which Turner said later yesterday that he was not aware of when he announced the arrests. Turner initially had said at a news conference that all but one of the 24 remained in jail, a statement that he later acknowledged was based on erroneous information given to him.

Turner mentioned the arrests during a monthly news conference yesterday at which he also announced a 4 percent increase in crime during March over figures for March 1981. The chief also displayed a 16-page "Metropolitan Police Department Improvement Plan," which Turner described as a mostly philosophical document outlining the department's "values and beliefs." He said the document would be the centerpiece for future efforts to improve police operations.

In kicking off the new "repeat offender project" last month, Turner and Mayor Marion Barry had stressed that undercover police would trail known criminals, catch them in the act of committing crimes and seek to have them jailed until trials.

Turner and Barry had said police would seek to have some chronic offenders jailed under "preventive detention" procedures. In such cases, criminal suspects can be held in custody pending trial if prosecutors can persuade a judge that the release of a suspect would pose a danger to the community, or that the suspect probably would not appear for trial.

Police Capt. Edward Spurlock, who leads the new squad, said that five persons -- including three juveniles -- were observed committing crimes, while 19 others were arrested on outstanding felony warrants.

Spurlock said none of the cases in the first week met criteria for preventive detention. He said that the persons arrested had an average of five or more prior felony arrests.

In reporting the March crime statistics, Turner said crimes against persons declined 9 percent compared to March 1981 figures -- a decrease that was more than offset by an in crease in crimes against property. Auto thefts and larcenies, for example, were up 19 and 14 percent, respectively.

For the first quarter of 1982, reported crime increased by 2 percent, with larcenies from autos, auto theft and rape each increasing by more than 10 percent. But Turner said that he was encouraged by a 7 percent decline in robberies.