Mayor Marion Barry, declaring he wants to send a message to criminals, yesterday announced a crackdown on crime in Washington that would put 242 more police officers on the streets by May and increase deployment of more than six dozen squads armed with shotguns to stake out frequently robbed businesses.

Barry also said the police department would establish an expanded 88-member squad to concentrate on apprehension of repeat offenders who police believe are involved in a disproportionate share of high profile crimes in the city.

The 242 additional street officers--an 8 percent increase that will raise to 3,273 the number of police on street patrol--will come from 168 new officers due to finish training in early May, 58 administrative officers to be reassigned from desk jobs and from 16 now-vacant administrative posts to be filled by officers who will work on the street, Barry said.

The announcement came just three days before Barry is scheduled to officially launch his campaign for reelection--a campaign in which the city's rising crime rate could be a major issue, according to preliminary polls and the campaign statements of several of Barry's announced opponents.

"We are not going to be locked in our homes. We are not going to be locked in fear," Barry said to the cheers and applause of many police officials surrounding him at a press conference in police headquarters. "Our residents are going to see more police on the streets."

Police Chief Maurice T. Turner added, "I want each and every one of the thieves, when they look at the TV news tonight to understand. I want it known. . . . We are putting officers in the back of businesses with bulletproof vests, and we're arming them with shotguns, and we're going to stop the holdups that are occurring in this city."

Yesterday's announcement capped a gradual departure on Barry's part from his past opposition to increasing the police presence in the city. Last year, for instance, he agreed to hire additional officers only at the insistence of Congress.

The Barry plan unveiled yesterday included:

Placing the reassigned and new officers on regular street duty and in undercover and narcotics assignments.

Creating by April 18 the 88-member career criminal squad that will "identify, arrest and incarcerate" repeat offenders. Turner said the police department has a commitment from U.S. Attorney Stanley S. Harris to give the program high priority for prosecutions. The city already has a 12-person unit, which largely does administrative work, according to a police spokesman.

Revoking more quickly the paroles of persons who are arrested for committing other crimes.

Asking the City Council to approve legislation that would permit off-duty police officers to take private jobs in the city while wearing their uniforms. Barry said the officers would be "deterrents to crime" where they worked and would be available to go on duty anytime a crime occurred.

Hiring up to 200 additional officers to bring the force up to its authorized strength of 3,880 uniformed officers. Barry said the city will use a new police entrance exam that he said would eliminate racial or cultural bias.

He said applicants would be ranked and hired according to test scores. Last year, Barry created a controversy when he attempted to hire new officers by lottery in what he said was an effort to offset the results of a biased police exam.

The test will be given April 10 at Ballou High School in Southeast Washington.

Turner said the department's highly publicized "War on Drugs," begun last year, would continue. That program has sent large groups of uniformed police officers on periodic sweeps through neighborhoods where drug dealers openly congregate.

"Narcotics and heroin traffic is still continuing," Turner said. "We're going to continue to arrest those individuals."

Police officials said that some stakeout squads have been used before in fast-food chains, small groceries and banks around the city that have been repeated targets of armed robberies.

Usually, the squads are made up of at least two officers. One of the two usually hides in the back of a store while the other either works undercover as a clerk or waits nearby on the street, according to police officials.

Officials said the squads would now be used in more situations and that the 88-member career criminal squad would also use stakeout techniques.

Last month, Turner credited the growing use of such squads for helping to hold down reported crime in the city for the month of Janaury. A police spokesman said that the increased number of officers on the street would allow expanded use of the stakeout teams.

Barry also announced yesterday that he will not appoint a permanent fire chief or director of corrections until after the Sept. 14 primary elections. Both posts became vacant recently with the resignation of Fire Chief Norman Richardson and the death of Corrections Director Delbert Jackson.