Three of the nine homicides in the District this past weekend were related and may have been committed by the same persons, who are being sought by investigators, Police Chief Isaac Fulwood Jr. said yesterday.

At a news conference about the weekend's carnage, Fulwood announced that starting Sunday, a citywide squad of 100 officers will go into action, targeting high-crime areas, known criminals and caches of arms to try to prevent crime before it occurs.

"They have a 90-day mandate to bring this under control," Fulwood said of the rash of homicides. Afterward, police officials will decide whether to change the tactics of the unit, called the "rapid deployment force."

The killings also prompted a pointed exchange yesterday between the major-party candidates for District mayor. Democratic candidate Sharon Pratt Dixon said the homicides stemmed in part from the "cumulative effect of years of failed leadership" when her opponent, Republican Maurice T. Turner Jr., was police chief.

Turner, who retired in July 1989 after eight years as chief, said it was "not logical" to link the killings to him. He questioned her knowledge of police work and of the streets. "I don't think Sharon Pratt Dixon is familiar with a lot of neighborhoods in far Southeast," Turner said.

Of the nine homicides that occurred between Friday evening and Sunday evening, seven were related to drugs, police said. There have been 372 homicides this year, compared with 352 at this time last year.

In the first of the two related homicide cases mentioned by Fulwood, two victims were found early Saturday morning in a vehicle on the unit block of Longfellow Street NW, police said. The victims were handcuffed behind their backs, their mouths were covered with duct tape and they were shot in the head.

In the related case, a man was found later Saturday a half-mile away, in the 6000 block of Sligo Mill Road NE, shot in the head. His hands were taped behind his back, and his mouth was taped shut. Both cases appeared to be drug-related, and detectives hope to make an arrest within one or two days, Fulwood said.

"There is something about people's value systems, when you can walk up, put duct tape over a man's mouth, blow his brains out all over the sidewalk and then go home," Fulwood said. "Something is wrong with that."

The killings generated a day's worth of dueling statements from the two mayoral candidates, and a joint appearance on WUSA-TV (Channel 9) devoted partly to the crime issue.

Dixon accused Turner of offering lame excuses by blaming some of the city's crime problem on his inability to persuade his former boss, Mayor Marion Barry, to hire more officers. Turner has said that he made his decision to retire in part because his repeated requests to hire more officers were ignored.

"If you feel that strongly about it, and if you feel it was in the best interest of the quality of life of the people of {the} District of Columbia, you should have stepped up to the bat," Dixon said. "And if indeed the mayor didn't respond, you could have quit a long time ago. That's what leadership is about."

After the television appearance, Turner suggested to a forum of senior citizens at the Edgewood Terrace public housing complex in Northeast that Dixon is afraid of being in some city neighborhoods. "I see her walking around . . . with a bodyguard," Turner said.

Turner has tried to portray himself as more in tune with the typical District resident than Dixon. Turner said that if Dixon, a former executive with Potomac Electric Power Co., was afraid and wanted to visit communities with him, "I'll walk with her and protect her."

Dixon reacted strongly to Turner's questions about her willingness to travel to all parts of the city. She said she had been "walking there a long time, I can tell you." Staff writer Rene Sanchez contributed to this report.