The number of drug addicts and drug abusers in Maryland increased by nearly 40 percent in the last five years, despite stepped-up enforcement of drug laws, state health officials said yesterday.

Citing a recently completed study, health officials estimated that 101,000 Marylanders, or about 2.4 percent of the population, have serious drug habits involving heroin, methadone, cocaine, marijuana, PCP and tranquilizers. A similar study published in 1978 reported about 73,000 persons abusing such drugs.

Richard Hamilton, director of the state Drug Abuse Administration, said yesterday that the figures for Maryland are similar to those in other northeastern states, but above the national average of 1.5 percent to 1.7 percent.

According to officials at the National Institute on Drug Abuse, addiction and abuse of drugs had been on a slow rise between 1979 and 1982, when it began to level off. Last year, the federal government estimated that about 19 percent of Americans used illicit drugs in the previous year.

The Maryland study found that the heaviest areas of drug abuse were Baltimore City and Prince George's County. The study did not count actual drug abusers but projected their total numbers based on the use of Maryland's 65 drug treatment centers.

Montgomery County had the fifth highest incidence of drug abuse, following Baltimore and Charles counties. Officials said the high ranking for rural Charles County was surprising and was probably caused in some part by the expansion of the Washington suburbs into that area.

Western Maryland and the Eastern Shore had the fewest drug addicts, according to the study. Howard and Anne Arundel counties were near the middle of the list.

In total, Maryland was estimated to have 39,777 heroin, morphine and methadone addicts, up about 21 percent from five years ago. Marijuana, PCP, LSD and other non-opiate users jumped by 50 percent in five years, from 40,624 to 61,698.

The study found that two-thirds of the male heroin users were black. Men outnumbered women among heroin users 3 to 1.

Hamilton said it was difficult to explain the statewide increase in drug abuse but suggested that high unemployment could partially be blamed.

"As people become unemployed they become frustrated and turn to alcohol and drugs," he said. "It becomes a vicious circle: because of the drugs he can't maintain a job. On top of that we have an increased availability of all kinds of drugs."

Hamilton said stepped up law enforcement pushed many addicts into treatment programs at a time of federal cutbacks in funding for those programs. But he said most of the lost federal funds were offset by increased state money.