The D.C. Police Department is investigating allegations that a police commander underreported crime in his Far Northeast district by downgrading serious offenses to lesser violations and improperly transferred a detective who complained about the practice.

Deputy Chief Isaac Fulwood, commander of the largely residential 6th Police District east of the Anacostia River and north of Pennsylvania Avenue, declined to comment yesterday on the probe, but said he expects to be cleared of any wrongdoing.

The investigation stems from a letter that the Fraternal Order of Police, a rank-and-file officers' organization, wrote to Chief Maurice T. Turner in which the FOP outlined six cases of reclassifications of serious crimes to minor offenses.

The letter charged that the six cases, which included changing attempted burglaries to the lesser category of vandalism or destruction of property reports, were only examples of a wider effort by Fulwood and top officials in the 6th District command to downgrade crime figures.

The FOP letter alleges that under Fulwood's policies -- spelled out to officers at roll-call meetings -- "street officers now know that it is not desirable for them to report offenses" that will be included in major crime statistics. The letter said that the policy has "distorted the analysis of criminal activity by . . . detectives" who are not getting an accurate picture of crime in the area.

Turner said yesterday a preliminary departmental report on the allegations was completed last week, but he has sent it back to Asst. Chief Marty Tapscott for more details and written statements. "There were a lot of questions unanswered," Turner said. He said he expected the probe to be concluded by early next week.

The FOP letter followed continuing complaints from officers after the abrupt transfer in late September of Det. Raymond Dyer, a 12-year veteran of the force. He said he was reassigned from detective work to scooter patrol "as shock treatment" for other disgruntled officers, who had objected to the reclassifications.

Dyer appealed his transfer to the International Brotherhood of Police Officers, which has filed a formal grievance in his case.

Dyer's case, which normally would have been reviewed within two weeks under the department's labor contract, has been held up until the broader investigation of the crime statistics is completed, officials said.

Crime in the District, a politically sensitive issue as the city heads into next year's mayoral and City Council elections, has fluctuated in recent months, with citywide increases of 5 percent in July over June, 4 percent in August over July and a decrease of 4 percent in September from August.

By comparison, reported crime in the 6th District wentup 25 percent in July, the first full month Fulwood was in charge, compared with June, and up again 5 percent in August. But in September, reported crime fell sharply, dropping 11 percent below the August figures, according to police department statistics.