The Philadelphia District Attorney's Office is scheduled to withdraw scores of cases Monday as prosecutors continue scrambling to drop arrests carried out by officers in a controversial narcotics unit, according to criminal justice sources.

One source in the court system, who asked to remain anonymous because he lacked approval to discuss the dismissals, said more than 100 prosecutions would be withdrawn.

If that happens, the number of recent cases dismissed would reach at least 270, surpassing the roughly 250 that were dropped in the late 1990s during the epic scandal involving the 39th Police District.

The current wave of dismissals started when District Attorney Seth Williams notified police Dec. 3 that his office would not prosecute drug arrests made by six members of the Narcotics Field Unit South.

The department immediately transferred the six. They are Officers Michael E. Spicer, Thomas Liciardello, Brian P. Reynolds, Perry Betts, and Brian Speiser, and Lt. Robert Otto.

Williams has not explained why he stopped prosecuting the officers' cases. The six have not been accused of any crimes and are in good standing with the department. They have not responded to requests for comment.

Almost all of the cases that have been dropped involved felony drug arrests. The defendants ranged from first-time offenders to people with long prison records. The withdrawals to date do not include cases in which there have been convictions. The six officers have been involved in about 2,000 arrests over the last decade, according to court records analyzed by The Inquirer.

John McNesby, president of the Fraternal Order of Police Lodge 5, has repeatedly criticized Williams and the transfers. But Common Pleas Court President Judge Pamela Pryor Dembe said in an interview last month Williams' action was "the right thing to do."

Most of the cases on the docket Monday are scheduled for hearing before Common Pleas Court Supervising Judge Sheila Woods-Skipper. As of last week, about 170 cases had been dropped, including 28 on Thursday.

Some defense lawyers said prosecutors had notified them of the planned dismissals. Others learned by word of mouth.

Attorney Mary Therese Maran said she surmised that two of her clients would have charges dropped when she saw their names on Woods-Skipper's court docket.

Other judges are also scheduled to handle dismissals, lawyers said.

Stanley M. Shingles, a Conshohocken lawyer, said his client Joseph D. Schweibinz, 57, had been scheduled for trial Aug. 5. But Shingles said he contacted prosecutors about the officers' involvement in his client's arrest and they agreed to withdraw charges.

Spicer is listed as the officer who arrested Schweibinz, who was accused in May 2011 of selling marijuana and who has a long history of drug arrests, according to court records.

As a spin-off to the dismissals, some lawyers are recruiting clients from among those who have had their cases dropped in preparation for lawsuits. Such civil litigation typically follows mass dismissals, with taxpayers footing the bill.

Just last week, Camden and the city's insurer agreed to pay $3.5 million to 88 people arrested by five narcotics officers, four of whom were found guilty of federal corruption charges. The fifth officer was acquitted. Philadelphia paid more than $4 million to settle suits from the 39th District cases.

In a letter sent recently to "prospective clients," attorney Gerald J. Williams said he was writing after obtaining "court records available to us."

"Charges against you were recently withdrawn or dismissed because of the involvement of certain officers with the Philadelphia Narcotics Unit, who may have falsified affidavits of probable cause or engaged in other illegal or unconstitutional activities," the letter said.

Gerald Williams, who did not respond to a request for comment, said in the letter his firm would be "happy to arrange" a consultation.