The Department of Labor, acting on a complaint of widespread employe drug use in its restrooms and corridors, has called in the D.C. police force to help curb trading in marijuana and cocaine.

After a rare, 21/2-month investigation by an undercover policewoman posing as a typist in Labor's black lung division, five employes have been arrested and charged with selling marijuana to their fellow workers.

Two others, one a typist at Labor and one presently unemployed, were arrested after the undercover officer bought some cocaine from them during a lunch-hour excursion to an apartment a few blocks away in Northeast Washington.

One police characterized the use of marijuana at Labor as "blatant." Other drug enforcement officials said the casual use of drugs on the job probably is not more widespread at Labor than at other federal agencies and reflects their increasing acceptance and general popularity.

Francis Kiley of the Labor Department inspector general's office confirmed that the agency requested the investigation after an employe complaint and said he "helped coordinate" the arrests. He declined further comment.

The undercover policewoman - who no longer is typing and filing at Labor - said she easily infiltrated the ranks of those getting stoned during the lunch hour.

"Basically, all you have to do is wear sunglasses and be able to talk their language," she said in an interview. Drug use is "a social thing, like a coffee break, only you smoke a joint instead."

The smokers, mostly young and single, often gathered around a noon-hour pipe of marijuana on the Labor Department roof or in a park across the street, according to the undercover officer referred to in police reports as "#244."

Then, for the rest of the day, the drug would make the workers "slow and drowsy" at their typing and filing, she said.

The sellers, not large scale operators, dealth mostly in amounts worth $10 to $30. A $10 bag will make about 10 cigarettes, police said.

Protected by civil service rules and an active union, the arrested workers have been allowed to stay at their jobs, pending trial, although two reportedly left for other reasons.

"They'll probably just get their hands slapped," said a supervisor in the black lung division, who asked not to be named. "I told them it won't affect my feelings toward them, as long as they do their jobs."

Other employes in the offices where #244 worked, posing as a typist, and where the attests were made, on the first, seconf and fifth floors, said they were "not surprised" by the arrests. Several indicated they were much more shocked by the fact that an undercover officer was planted among them. Some just giggled.

In keeping with police department policy, the undercover officer said she avoided using any drugs herself, coming up with various excuses when invited to "get high" or "get down."

The purchases were made in restrooms or in hallways, she said, and the marijuana was usually contained in a manila envelope about the size of an open book of matches, easily concealable in the palm of a hand.

Among those lower-echelon employees, whose pay is in the $8,000 to $10,000 a year range, there was little demand for the much more costly cocaine, which sells for about $100 a gram, according to #244.

"If you wanted a large amount, you had to place your order a day in advance."

The maximum penalty the sellers could be assessed is a year in jail and a $1,000 fine, police said.

The profits from the Labor Department trade probably amounted to a few hundred dollars a month in most cases, and a few hundred a week for one seller, according to a source on the narcotics squad. Of those arrested, only one employe had a prior record. She was believed to be a sometime heroin user selling marijuana to support her occasional craving for heroin, he said.

The investigation grew out of a complaint by a disgruntled woman employe who received an "unsatisfactory" job performance rating from her supervisor , police said. She retalitated by turning in a 14-page statement naming drug sellers around the office and complaining that many of her co-workers were stoned, yet they received "satisfactory" ratings.

The narcotics squad usually resists spending its time and money on such an investigation unless a large operation or hard drugs are involved, police sources said, but was persuaded to do so this time by an influential former District police officer now working at the Labor Department.

While a small number of high-ranking Labor Department officials, including Secretary Ray Marshall, reportedly knew of the presence of the undercover officer, her immediate supervisor, Jim Robinson of the black lung division, did not.

The officer took the civil service exam, made a score of 98, and entered as a GS3 through regular channels, she said.

"When I first started, it was a problem because my supervisor wouldn't give me any freedom. He complained constantly that I was out in the hall socializing instead of typing and filing . . . I had to go over his head to get him off my back, so I could do my real job."

How did she like government work? "Terrible," she said. "I was glad to get back on the street."