D.C. Mayor Marion Barry decided last week that police should proceed with Saturday's mass crackdown on drug trafficking, even though law enforcement officials knew it could worsen overcrowding at the D.C. Jail, city officials said.

More than 400 persons were arrested in the citywide sweep.

After Barry had decided the mass arrests should go forward, Superior Court Chief Judge H. Carl Moultrie I told police officials on Friday that the crackdown could add to the jail overcrowding, but Police Chief Maurice Turner again approved the plan, Turner said yesterday.

The behind-the-scenes controversy continued on Sunday, sources said, when top officials of the U.S. Attorney's office decided not to prosecute a large percentage of those arrested for drug offenses Saturday, but reversed themselves after D.C. police officials threatened to hold a press conference criticizing the prosecutors for not pressing the cases.

These disclosures came yesterday as arraignments proceeded in a special courtroom in Superior Court for 80 persons arrested in the sweep and jailed over the weekend.

The police operation, called "C-Note Sevenfold," lasted for seven hours on Saturday and involved two separate phases in each of the city's seven police districts.

In all but one district, officers set up roadblocks and checked drivers' licenses and registration, in what officials called a diversionary tactic. Other officers in each district were covertly observing areas where illegal drugs were being sold, and arresting buyers after they left the area.

The sweep represented a shift in D.C. police procedure because officers were pursuing drug buyers as well as sellers. For the past several years, D.C. police have not concentrated on arresting buyers, and prosecutors frequently have declined to pursue cases such as marijuana possession because doing so might stretch law enforcement resources too thin.

There had been months of planning for the sweep, after police Deputy Chief James Kelly, of the 7th District, convinced his superiors that experiments with the procedure in his district suggested it could be used city-wide.

But the prospect of having up to 500 new inmates into the D.C. Jail was not an inviting one to some officials.

The jail in Southeast Washington, designed for 1,355 prisoners, houses more than 2,400. U.S. District Court Senior Judge William B. Bryant has said that he may hold Barry and other city officials in contempt of court for not moving to alleviate the overcrowding. Bryant ruled that city officials are in violation of strict conditions he set last year in a decision allowing two inmates per cell.

Despite his personal stake, Barry told Turner to proceed with the operation, officials said.

"The mayor said to go ahead," said his spokeswoman, Annette Samuels. "The mayor's position was, 'We do have a problem in the facility. But we also have a problem on the street. We have to address both problems.' "

On Friday, Moultrie called Assistant Chief Marty M. Tapscott, head of field operations, who was acting as chief of the police force because Turner was away from work, officials said. Moultrie expressed concern that the operation might add to overcrowding at the jail and give the signal that the city takes Bryant's concerns about overcrowding lightly.

Tapscott called Turner Friday to tell him of Moultrie's concerns, and Turner gave the project another green light.

Moultrie could not be reached for comment yesterday.

Some 448 people were arrested between 2:30 p.m. and 9:30 p.m. Saturday, the vast majority of them in the drug sweep. Police said 290 of the arrests were for drug-related offenses, mostly misdemeanors involving possession of marijuana and PCP.

Some other arrests were for license violations and such offenses as driving while intoxicated and disorderly conduct.

"The idea was to disrupt the flow of drugs, give a person a reason not to come back to buy drugs," said Capt. Bruce McDonald, who ran the operation for the Third District. "The idea is to get the word out."

The local U.S. Attorney's office usually decides to "no-paper"--or not process--such misdemeanor charges as marijuana possession. One exception, traditionally, is when the D.C. police undertake a major crackdown such as Saturday's.

But on Sunday, officials in the U.S. Attorney's office told police officials that they would drop charges of marijuana possession, law enforcement sources said.

D.C. police officials, including Kelly, threatened to call a press conference to criticize that decision, and prosecutors agreed to press the cases, sources said.

Commenting last night, however, principal assistant U.S. Attorney Joseph E. diGenova said: "The ultimate decision whether to proceed on any or all of these cases remains, as always, in the hands of the prosecutor. When these cases are all reviewed, that decision will be based on all the facts, on standard prosecution guidelines and on the effect of these cases on an overloaded criminal justice system."