All of them were recent victims: A group of friends gathered in an Adams Morgan apartment, clerks at a Northeast seafood restaurant and a Southeast fast-food restaurant,a middle-aged woman walking to her parked car in upper Northwest Washington.

In every case, strangers approached, pointed guns and demanded money during a seasonal crime wave that hit Washington harder than in previous years. D.C. police said more robberies and muggings were committed last month than in any single month during the past decade.

The number of reported robberies in December was up 22 percent from November, and police say that January's statistics are likely to be high as well. In the first four days of 1982, there were 68 robberies, thefts and muggings.

"I hate to equate it with the need for additional money to pay the Christmas bills," said D.C. Robbery Squad Captain Thomas Novak, "but I know they're not doing it to pay their income taxes."

Although December's robbery statistics were the highest in a decade, the number of robberies during 1981 also increased dramatically. Police estimated there were 10,423 robberies last year, a 17 percent increase over 1980 and a 51 percent increase over 1979. The reasons for the overall increase include inflation, unemployment and the city's heavy drug traffic.

Figures provided by police include robberies committed by threat and force as well as armed robberies committed with weapons ranging from handguns and knives to screwdrivers and baseball bats. The number of armed robberies last year increased more rapidly overall to 6,210, a 31 percent rise over 1980 and up 94 percent over 1979.

"There's a trend toward more violence in the commission of these cases. There are definitely more guns," Novak said.

Police Chief Maurice T. Turner said recently that his department has watched with frustration the soaring number of armed robberies and thefts, and that the department has stepped up its efforts to control both crimes.

Street thefts and muggings are most frequent in crime-heavy areas such as the drug- and prostitution-riddled 14th Street corridor. But police say that robberies and muggings are prevalent throughout the city and that once-cozy residential neighborhoods such as those along upper Connecticut Avenue and in Adams Morgan are increasingly vulnerable as well.

Two weeks ago, a 28 year-old artist was robbed in an Adams Morgan apartment. She was one of 19 robbery victims in the city that day.

"I ran to jump out of the window," the artist said nervously several days later. When two men barged into her sublet apartment, she had tried to escape. "The man was in a military stance with a gun pointed at me," she said. "He said 'Stop or I'll kill you.' "

For the next two hours the woman and three guests were forced at gunpoint to lie face down while the men took turns loading her typewriter, clothing, color television, fur coat, tape recorder and other belongings into a car. They also took a portfolio with two posters and 11 just-completed original drawings, the sum total of her year's work as an artist.

"Everything else I could replace," she said. "They've ruined a year of my work.

"My friends and I have been absolutely terrified after this. I was sedated for three days, petrified," said the woman who, a week after the incident, still feared for her safety and asked not to be identified. "They could want to come back to get rid of their victims," she said.

Police say they are trying to curb robberies and drug dealing by more arrests, foot patrols and special projects. They also plan to place policemen armed with shotguns in some retail stores and other businesses plagued by crime.

A joint pilot project by the D.C. Police Department and the federal Bureau of Alcohol, Tobacco and Firearms to find where all the guns are coming from was ended shortly after the Reagan administration announced that the bureau would be disbanded.

"Quite frankly, we're at our wit's end," said Novak, noting that his 28-member investigative unit is swamped with robbery cases.

Novak said citizens can do a lot to protect themselves from muggings and street holdups, however, just by being aware of their surroundings. Most of the time-tested advice about not going out alone and avoiding strangers and shortcuts is the best advice, Novak said.

"It's the same thing as defensive driving," he said. "You don't drive without looking down the road."