A federal jury considering drug distribution charges against a McKinley High School student arrested by a member of the D.C. police department's undercover "school squad" was dismissed yesterday after it was unable to reach a verdict.

U.S. District Judge Louis F. Oberdorfer declared a mistrial in the case of Major H. Unger, 19, of 111 Franklin St. NE.

He set a new trial date for Sept. 11.

During the three-day trial, defense attorney Thomas Lumbard showed that the undercover police officer who had identified Unger as the person who sold him PCP-laced marijuana on Oct. 25 filed official reports showing that he attended all classes at the school on Nov. 29, Dec. 23 and 24, and Jan 27, days that no classes were held.

D.C. Officer James Simpson, a rookie who was enrolled as a student at McKinley, also reported that he saw Unger at school on days when official attendance records showed neither was there. Simpson was responsible for the arrest of seven students, including two juveniles, on drug distribution charges that carry sentences of up to 30 years because the sales were made on school grounds.

Charges against one of the students were dismissed earlier this month because of discrepancies in Simpson's identification of the youth.

A McKinley teacher also was prepared to testify that the youth was taking a test at the time of the alleged drug sale.

Two other students have pleaded guilty to lesser charges, and one was convicted after a trial. Because of the problems found with four of the officer's reports, Oberdorfer ordered prosecutors to release to Lumbard all paper work generated by Simpson during his investigation.