Aside from possibly disqualifying a person from a seat on the Supreme Court, occasional use of marijuana is unlikely to cause lasting health problems.

But a growing body of research data is yielding a scientific consensus that prolonged regular use of this drug entails significant risks such as short-term memory loss, lung damage and possible psychic dependency.

"The data is chipping away at the image that this is a harmless high," said Dr. Robert L. DuPont, a psychiatrist and former director of the National Institute on Drug Abuse whose own views about the drug have toughened in the past decade.

"A lot of people who said terrible things about pot and were called anti-intellectual know-nothings two decades ago are turning out to be right," said DuPont, who heads the Center for Behavioral Medicine in Rockville.

Scientists generally agree that 1970s-vintage "reefer madness" scare stories about the dangers of marijuana were just that -- scare tactics based on little hard data.

Scientific research on marijuana use has boomed since 1964, when the drug's active ingredient, delta-9-tetrahydrocannabinol or THC, was identified and then chemically isolated.

As with any drug, the effects vary with the dose, the frequency and duration of use, and whether it is used in combination with other drugs such as alcohol. Experts agree that occasional use does little or no lasting harm to health.

Yet sometimes former users can experience unexpected political effects from smoking marijuana. Just ask Douglas Ginsburg, who last week was forced to withdraw his name from consideration as President Reagan's choice to fill the current vacancy on the Supreme Court -- after a furor erupted because of the disclosure that he had occasionally smoked the illegal drug in the 1960s and 1970s.

And intoxication itself -- the "high" marijuana brings -- can be hazardous by impairing judgment and coordination for up to 24 hours.

"The major danger of marijuana is to get stoned and then go out and drive," said David P. Friedman, deputy director of preclinical research at NIDA. "Unfortunately, you don't realize how impaired you are."

Marijuana use has stabilized and declined slightly since the late 1970s. The most recent national survey by NIDA in 1985 found that nearly 62 million Americans 12 and older -- about one in three -- have tried marijuana at least once. Among college students, the rate of marijuana use declined from 51 percent in 1980 to 42 percent in 1985, NIDA reported.

At the same time, the health consequences may be greater today than in the 1970s, because the potency of the drug is greater, said Dr. Victor H. Cohn, professor of pharmacology at George Washington University Medical Center and former scientific adviser for drug abuse policy under President Carter. In 1970, a typical marijuana joint or cigarette contained about 1 percent THC. Today, the THC content can reach 5 or even 10 percent.

Pot users also tend to be starting younger these days, and experts worry that the drug's effect may be greater during the developmental stage of growth and sexual maturation.

"Kids are far more vulnerable than adults," Cohn said.

The difficulty in estimating long-term health effects of marijuana is compounded by problems in measuring dosages. Unlike cans of beer, for example, joints vary widely in potency. What's more, there is a long latency period for some possible effects such as cancer of the lung or psychiatric disorders, and marijuana has come into widespread use in the United States only in the past two decades.

"There are 16 million guinea pigs out there," said Cohn, referring to one estimate of the number of regular pot users in the United States.

Advocates of legalization of marijuana have long argued that marijuana is no worse than alcohol or tobacco, but health experts say that reasoning misses the point.

"If that's the standard," said psychiatrist DuPont, "an awful lot of things would get in under that blanket. {Alcohol and tobacco} are two principal preventable causes of death in the world."

"People say it's not as dangerous as alcohol," said Dr. William T. Beaver, professor of pharmacology and anesthesiology at Georgetown University Medical Center. "That may be true, but alcohol is a very dangerous drug."

Still researchers now know that marijuana affects a variety of human organs and bodily systems, including: The brain. Marijuana impairs motor coordination and short-term memory, slows learning and can distort sensory perception. Longer-term effects on brain function are controversial and still under study. The lungs. Heavy smoking of marijuana, which burns at a higher temperature than tobacco does, irritates the large airways of the lungs and can cause bronchitis. Marijuana smoke also contains a higher content of tars than tobacco smoke does, though smokers usually use far less pot than tobacco. Nevertheless, pot smoking is a strongly suspected cause of lung cancer, though definitive evidence is lacking and the effect of marijuana alone is difficult to single out in people who smoke both tobacco and pot. The cardiovascular system. Marijuana makes the heart work harder, usually by increasing the heart rate and sometimes by increasing blood pressure. This poses a temporary risk to people with hypertension and heart disease, though the effect on healthy people remains unknown. Reproduction. In animals, THC has been shown to lower the concentration of pituitary hormones that control reproductive function. It slightly lowers sperm production in men and interferes with ovulation in women, though the effects on fertility are unclear. THC crosses the placenta and in large doses can cause birth defects in laboratory animals, but its ability to cause birth defects in humans remains unknown.

Researchers at Wake Forest University School of Medicine in Winston-Salem, N.C., reported last year that THC causes effects on the brain that are similar to those caused by normal aging. Rats given high doses of THC for up to eight months showed reduced numbers of neurons, or brain cells, and exhibited changes in glial cells that are normally seen after brain damage. The significance of these findings for humans remains unclear. Similar studies in monkeys are under way at the National Center for Toxicological Research in Pine Bluffs, Ark.

Scientists also are studying the possible effect of marijuana on immune response to see if it could increase susceptibility to viruses from the common cold to AIDS, but results so far are incomplete.

Another controversial issue is whether marijuana is addictive.

"Clinically, there can be no doubt that some people who use this drug get into very serious trouble," said Georgetown's Beaver. "Most don't, but some do. They escalate {the} dose and become psychically dependent on it."

A recent study at the Medical College of Virginia demonstrated withdrawal symptoms -- evidence of physical dependence -- in monkeys who were given a low but continuous dose of intravenous THC for 10 days or more and then taken off the dose. Within a day after the dose was stopped, the monkeys, who had been trained to press a lever to get a reward of banana-flavored monkey pellets, seemed less interested in performing the task.

"They look fine and they eat, but they're not responding," Harris said. "We're calling it behavioral dependence."

Some health officials are also concerned that marijuana use may lead to trying "harder" drugs.

Richard Clayton, a sociologist at the University of Kentucky, has been studying the correlation between marijuana use and other drugs for more than a decade. At first he was skeptical of the correlation, but detailed analyses of national data have changed his mind. Though marijuana use does not necessarily cause use of other drugs, Clayton believes, it can be an entree into the drug world.Among people who have never used marijuana, Clayton found, fewer than 1 percent used cocaine. Among those who had used pot at least 1,000 times, 73 percent also used cocaine. More than 90 percent of the people who use both drugs used marijuana first.

Clayton and his colleagues looked at 32 possible common factors that could have explained both the tendency toward marijuana and cocaine use -- and ruled each one out statistically.

"We were shocked," Clayton said. "We sat and looked at those data 37 ways from Sunday because they went against the commonly accepted notion." But he is now convinced that for some users, marijuana is the gateway into the illegal drug market that can lead to other drugs.

"Most people who use marijuana do not use cocaine," he said. "But the more you use marijuana, the greater the risk that you will use cocaine or heroin. The key is that it puts you in touch with the illicit market."