The Prince George's County Human Relations Commission last night rejected a motion to investigate allegations that county police operated a "death squad" in 1967.

After two hours of arguing and name-calling, the commissioners voted 6 to 4 against by Jeseph M. Parker to commence a "study-survey" of allegations by a former police officer and a former police informer -- reported in The Washington Post on Feb. 11 -- that county police arranged at least one armed robbery that resulted in the shooting death of a teen-ager.

After Parker's motion was defeated, the commission adopted a suggestion by Chairman F. John D'Eustachio Jr. that a committee be appointed to monitor any investigatin of the "death squad" that is conducted. County Executive Lawrence J. Hogan has asked the Justice Department to consider investigating the allegations and has said he would like a "disinterested third party" to conduct an investigation.

Parker had argued that the commission itself is "eminently qualified" to conduct an investigation, adding, "We are people who are not encumbered with prejudices that would [make us] unfit to give a report."

Each of the 11 commissioners in turn supported or attacked Parker's suggestion, and one, William Hudelson, said he would disassociate himself from the commission if it undertook such an investigation.