The district attorney yesterday threatened to take legal action against three Downtown McDonald's restaurants after police arrested an employee of the Smithfield Street store on charges of selling drugs to an informant in the rest room.

District Attorney Stephen A. Zappala Jr. said his office warned McDonald's headquarters in Illinois to stop drug activity around all three stores or face "nuisance proceedings."

The arrest and the warning are part of an effort by his office, the mayor's office, Pittsburgh police and the Port Authority to drive out nuisance crimes from the Downtown business district.

"The continuing cooperative effort that has been under way to keep Downtown a destination for families depends in large part on there being confidence in public safety," Mr. Zappala said in a statement. "I and other officials will not tolerate any type of criminal behavior that erodes that confidence and interferes with the positive developments taking place Downtown on a daily basis."

That announcement followed the arrest of John J. Eckard, 48, an employee of the McDonald's in the 500 block of Smithfield, after two controlled buys in February arranged by the DANET drug task force.

According to affidavits, Mr. Eckard sold Clonazepam, a muscle relaxant, and the anti-anxiety drug Xanax to an informant who told police that he had bought prescription narcotics from Mr. Eckard in the past and that Mr. Eckard sold drugs "openly" at the restaurant.

On the morning of Feb. 24, the informant wore a wire and bought 11 Clonazepam tablets from Mr. Eckard for $20 inside the rest room, according to the affidavit.

Three days later, police said, the same informant bought five Xanax tablets for $20 from a man identified as "Tommy," whom Mr. Eckard had pointed out as a seller. That deal also happened in the rest room, police said.

Police charged Mr. Eckard early yesterday with conspiracy, possession, possession with intent to deliver and delivery.

Mr. Eckard was identified in a criminal complaint as a manager of the McDonald's, but employees there said he was a maintenance worker and crew trainer who had worked there for more than five years.

Employee Lisa Monrowe, 20, of the North Side, said the Smithfield Street store is often populated by drug addicts, and police are a frequent presence. But she said she had never heard anything about employees peddling narcotics and was surprised at the allegations against Mr. Eckard.

Mr. Zappala said his office has warned McDonald's corporate headquarters to take "immediate and permanent measures" to stop drug dealing or face legal consequences.

Under Pennsylvania law, a business can be shut down if prosecutors can show that it qualifies as a nuisance.

McDonald's, which also operates on Wood and Stanwix streets, issued a statement yesterday.

"We take these allegations seriously. Operating safe restaurants will always be a priority for McDonald's. ... McDonald's and our franchisees are fully cooperating with the district attorney's office and police department on this matter."

Mike Manko, spokesman for Mr. Zappala, did not return a message late yesterday.