More than two-thirds of those charged with drug dealing in the District hold legitimate jobs, according to a new report that characterizes the street drug business as a "lucrative underground form of moonlighting."

That finding, which counters a long-held assumption that street dealers do not hold jobs in the regular economy, was one of several characteristics to emerge from a report released yesterday by the Rand Corp., which studied street drug dealing in the District in the late 1980s.

The study found that typical dealers earned about $800 a month, or $7 an hour, at a legitimate job at which they worked close to full time. Those who sold drugs daily earned $24,000 a year tax-free, working on the streets about four hours a day, at a rate of about $30 an hour.

The study found that the numbers "are vastly less than the figures the popular press frequently reports. Nor are they the earnings from which Mercedes are purchased. On the other hand, they represent an income level far beyond the attainment of this same population in legitimate employment."

The study focused primarily on young black males, which it said represented the vast majority of District residents charged with drug selling from 1985 to 1987. It found that the number of black men between 18 and 20 who were charged with drug selling in the District between 1985 and 1987 was equal to one-sixth of all the black males in that age category in the District at that time. The study projected that if that trend continues, nearly one-third of that age group could be expected to be arrested for selling drugs by the time they reach 29, the report said.

The study relied on three principal sources: records from the D.C. Pretrial Services Agency on people charged with crimes in D.C. Superior Court from 1985 to 1987; interviews with 186 D.C. residents on probation who reported earning income from drug selling in the six months before entering probation; and a 1988 Urban Institute survey of 387 ninth- and 10th-graders in the city's poorest neighborhoods.

The report, sponsored by the Greater Washington Research Center and the Rockefeller Foundation, examined only street dealing. It also does not reflect what generally are considered recent encouraging signs of a possible leveling or reduction in illegal drug activity in the District -- from a decrease in the number of drug-related killings to a steady drop in the number of people testing positive for drug use who are arrested in the District.

For example, although the total number of homicides in the District is up, the number of drug-related homicides dropped from a high of 60.5 percent of all killings in the District in 1988 to an estimated 44 percent for 1990, said Inspector David Bostrom, director of the D.C. police department's planning and research division.

The report's authors and sponsors also were careful to stress that the findings did not reflect a complete picture of the city's drug sellers, but only its most accessible.

"Those who sell drugs in private settings, such as college dormitories, are subject to little risk of police apprehension," the report said. "The complete population of District resident drug sellers may have substantial numbers of sociodemographic groups other than young black males."

Those assurances did little to quell the reaction among some black leaders and educators who characterized the study as another in a long series of recent reports depicting the black community in bleak terms.

"It's painting the young black with a single brush by only focusing attention on the pathology of the urban black male," said Robert L. Woodson Sr., president of the National Center for Neighborhood Enterprise, a nonprofit organization. "I believe you learn nothing about studying failure except how to create it . . . . If you want to learn how to play the piano, would you go to five people who failed to learn to play?"

Karen Hastie Williams, co-chairwoman of the Rockfeller Foundation for the Committee on Strategies to Reduce Chronic Poverty, disputed the criticism yesterday and pointed out that the study reported that more than 40 percent of those arrested in the District on drug possession charges live outside the city and of those, 30 percent were white.

"This is not just a black issue," Williams said. "This is a metropolitan-wide problem."

In what its authors described as its most distressing finding, the study found that trying to steer young men away from the drug trade by offering alternative employment may be far more difficult than expected.

"Even creation of considerably higher-paying legitimate jobs probably wouldn't get us very far," said Peter Reuter, who wrote the report along with Robert MacCoun and Patrick Murphy. "Dealers would still have smaller total incomes than they can earn now by supplementing their regular wages with drug selling."

Among the findings of the report:

More than 24,000 District residents sold drugs on the streets in 1987, with slightly less than half being regular dealers. The total net earnings from street drug markets in 1988 were estimated to be $350 million, compared with $1.2 billion in legal income reported in 1988 by black males aged 18 to 40 years old.

The typical drug dealer reported spending more money on clothes than on housing or food. According to the report, a quarter of the drug dealears said they spent no money on housing while more than 80 percent said they made monthly purchases of clothing. The majority interviewed said they typically spent in a month: $250 on housing, $150 on food, $275 on clothing, $100 on transportation and $201 on other expenses. More than half said they typically spent $585 a month to support someone outside their household.

Only 11 percent of 387 ninth- and 10th-grade boys interviewed in the city's poorest neighborhoods reported using illegal drugs in the previous year, but one out of six said they had sold drugs. Seventy percent of the youths who sold drugs reported using drugs, and more than 70 percent of the adult drug dealers said they had used a drug other than marijuana in the previous six months.

Street drug dealers who sold drugs more than one day a week faced more than a 1 in 5 chance of been imprisoned for every year they sold drugs, a more than 1 in 14 chance of being seriously injured and a more than 1 in 70 chance of being killed, a fatality rate that the study said was 100 times greater than that of the general work force.

Although the study concluded that the options "for reducing the extent of street drug selling are limited," its authors did make several recommendations. They included increasing the criminal sanctions for drug users, educating youths about the high risks involved in drug dealing and improving employment opportunities for youths who are not yet involved in the drug dealing.