Joseph D. Vasco Jr., second highest ranking official of the Prince George's County police department, denied in federal court today that he helped stage a series of robberies in 1967 in which two suspects were shot and killed and others arrested by waiting police.

Asked repeatedly by attorney Barnet D. Skolnik, representing plaintiffs in a $9 million civil rights lawsuit against police, if it was considered proper in 1967 for police to instruct informers to recruit participants for crimes, Assistant Chief Vasco answered, "That would not be proper."

Families of the two slain men, plus two other men arrested in the so-called "death squad" incidents, sued Vasco and two other police officials after published reports of the allegations in The Washington Post in 1979.

Plaintiffs accused Vasco, Capt. James Fitzpatrick and retired major Blair Lee Montgomery of rigging a series of five robberies and burglaries of convenience stores in 1967 by directing informers to recruit acquaintances for the crimes in exchange for help in getting pending charges against the informers dropped.

Police have denied the accusations, saying the informers came to them with tips about planned robberies and burglaries. Detectives then routinely staked out the targeted stores, police said.

Vasco acknowledged that in some cases, detectives suggested specific times and locations for robberies that informers told them were being planned. He said police suggested late-night hours or geographically remote sites to minimize harm to innocent passersby who might get caught in a cross fire between staked-out police and criminal suspects.