A Prince George's County police official testified today that a key witness against Assistant Police Chief Joseph D. Vasco Jr. in a $9 million civil rights lawsuit here was motivated by a "vindictive attitude" and had pledged revenge against Vasco for allegedly ruining his career.

Lt. Robert A. Miller told a federal jury that retired police officer John R. Cicala told him in 1977, using obscene language, that he planned to take revenge on Vasco, who he said had ruined both his police career and his retirement benefits.

Miller's testimony follows similar testimony last week by another county officer, Sgt. John M. Calhoon, who said he overheard Cicala tell a group of acquaintances at a party that he would "get back" at Vasco.

Cicala, who retired in 1977, is the only police witness to testify so far against Vasco and two other officers accused of staging a series of so-called "death squad" robberies in 1967 in which waiting police shot and killed two suspects and wounded another. Several other suspects were arrested.

Cicala said the incidents were planned from "A to Z" by Vasco and others, who he said instructed police informants to recruit unwitting participants to hold up a series of convenience stores that police then staked out. The two other police defendants in the lawsuit are Capt. James Fitzpatrick and retired major Blair Lee Montgomery.

The three have denied the allegations, saying the informants came to them with tips about planned robberies and that police then staked out the targeted stores in the proper manner.

When Cicala testified in December in the trial, he acknowledged under cross-examination that he was bitter that the county refused to grant him a work-related medical disability retirement pension at 70 percent of his base pay. Instead, he got a 50 percent pension, according to testimony today.

Cicala also testified he was fired, but later reinstated, for refusing to pose as a clerk in one of the convenience store stakeouts in 1967. He said at the time that he feared for his life but also felt the stakeouts were "legally and morally wrong." Several police witnesses have testified that he told them only that he was afraid and made no mention of the legality or morality of the stakeouts.

Both Miller today and Calhoon last week said Cicala indicated deep bitterness about his career--in 17 years he never got above the rank of officer first class--and blamed his lack of advancement on Vasco, who had risen swiftly through the ranks to become number two man on the county police force and presumably could influence Cicala's status.

In other testimony today, retired police major Joseph R. Hill, who had been commander of the detective bureau in which Vasco, Fitzpatrick and Montgomery worked in 1967, praised the three as "capable, efficient . . . and professional." Hill said he was unaware in 1967 of any allegation that the three men instructed informants to recruit participants for crimes.

Families of the two men killed in the stakeouts and two other men arrested in the incidents contend in their $9 million lawsuit that the police actions violated their civil rights and deprived them of due process of law.