Not long ago in Washington, buying hard drugs was largely an across-the-board proposition--go to a dealer, hand over the money, get the drugs and move on.

In the last three years, however, police surveillance has increased, and sophisticated, major drug dealers, seeking to shield themselves from arrest, have developed an elaborate system of runners, jugglers, holders, stash men and money men--an army of drug peddlers in which many of the newest foot soldiers are children and teen-agers.

Items from D.C. police records:

* Nov. 12, 1981: A man approached a 15-year-old Northwest Washington youth in the 1300 block of Wallach Place NW and handed him cash. The 15-year-old, a runner, directed the man to his 14-year-old sister standing a few feet away. The girl, a holder, handed the customer a pink diet pill used as a heroin booster and sold illegally for $20 each. All three people were arrested.

* March 26, 1982: Police received a tip that an 11-year-old boy at a 24-hour variety store in Northwest Washington was holding drugs for a dealer. In his jeans' pocket, they found two wax packets of heroin, which sell for $40 each on the streets. The boy told law enforcement officials an adult gave the drugs to him.

* April 17, 1982: Two men met outside an apartment building in the 1400 block of W Street NW; one handed the other a sum of money and was directed to a 15-year-old girl a few feet away. The girl pulled a packet of heroin from her pocket and handed it to the customer. The girl was arrested later with 14 wax packets of heroin worth $560 in her possession.

She was charged with possession of heroin and sent to Cedar Knoll, one of the city's juvenile detention facilities in Laurel. Her mother said she had been told that her daughter was addicted and selling drugs to support her habit. The girl escaped from Cedar Knoll last week, the mother said.

The role of children and teen-agers as intermediaries in Washington's drug trade came to light again last week when a 12-year-old girl was arrested in Anacostia with 15 packets of heroin in her backpack.

More juveniles were arrested for selling drugs last year than ever before. In 1981, 58 were arrested for distribution, compared to 18 in 1980. They ranged in age from 13 to 17.

"They come in here like Jimmy Cagney," said Lt. Ronald Harvey, head of the drug unit in the Third District, which is the largest center of drug trafficking in the city.

"Everybody in the unit feels especially angry when it's a small kid," said officer Phil Burton, who has worked in the unit for the past year. "What we see happening more and more are kids being used as holders."

"We are used to dealing with 30- and 40-year-olds, not little kids," Burton said. "As a general rule, policemen hate it when kids are abused and victimized. Most of the people that work this unit have younger brothers and sisters."

Most of those arrested are first offenders and end up being released or placed on probation when they go to court, officials said. Adults would receive stiffer terms, law enforcement officials say, and the lighter penalties are one of the advantages of youths being involved in the drug trade.

Some young offenders have been sent to the children's center, but officials say few seem bothered by such punishment. "So, you go to Cedar Knoll for six months," said Sgt. Larry Ware, a drug investigator at the Third District, describing the attitude of some children. "So what?"

The new system of drug sales breaks up the process. Runners and jugglers collect money from customers and direct them to holders or stash-men. In some instances, when runners get a certain amount of cash, they turn it over to a money man nearby.

Meanwhile, the dealer may or may not be on the scene. If he is, he does not touch the money or the drugs. All of his activity takes places somewhere else--away from police surveillance.

Court records show that the number of juveniles arrested for involvement with hard drugs is rising, while the number arrested for marijuana is declining.

In March, for example, there were eight arrests for possession of marijuana and 26 arrests for hard drugs, such as heroin. In comparison, in March 1981, police arrested 26 juveniles for possession of marijuana and 11 for hard drugs.

According to D.C. police, 343 juveniles were arrested for the sale and possession of drugs in 1981 compared to 315 in 1980.

Law enforcement officials said that in the majority of cases involving heroin, the youngsters charged with selling the drugs are not drug users.

Officials said many of these children see holding or selling drugs as an opportunity to make quick money in times of rising unemployment.

"The economy is getting tighter and tighter," said Ware. "Mama doesn't have the money to get this or that for her son or daughter. The dealer says, 'Sell this for me and I'll give you $100 or $200.' "

In the Third District, 50 juveniles were arrested in the past 16 months for the sale and possession of drugs. Twenty were arrested for heroin; 11 for Preludin, the pink diet pill called "Bam" on the street and used as a heroin booster; 18 for marijuana, and one for PCP. So far this year, 13 juveniles have been arrested; 2 of them for selling heroin and 7 for holding heroin.

The Third District drug unit arrested one 14-year-old girl twice within a two week period for possession of heroin. Most of the juveniles refused to tell police for whom they worked.

Police said many of these youngsters are not aware of the consequences of their actions. "It's a little fun thing for them to do and pick up a little money," said Lt. Harvey.

Ron Clarke of RAP Inc., a drug rehabilitation center, said the small number of youths who get involved in drug sales are just reacting to their environment.

"You have a different breed of kids," Clarke said. "They see things on television. That's what they want. We are talking about a system that encourages young people to move toward a collection of things . . .They don't see what they are doing as immoral. They are surviving."