Ruth knows that smoking marijuana, once virtually ignored by the public and police, is now considered "a very deviant thing. It's very taboo."

The 40-something San Francisco professional is married, has children and a respectable job. She knows that even though California's marijuana law is still relatively lenient, a drug bust could threaten her livelihood.Yet she still smokes high-grade sinsemilla several times a week.

Why?

"It's a very nice high," she said. "Often in these drug stories, people forget to mention that part."

Ruth is far from alone. Marijuana is the most popular illegal drug today, the crack epidemic notwithstanding.

Perhaps as a result, 38 states arrest more people for marijuana than for cocaine and heroin combined, government statistics show. Last year, almost 400,000 people were busted on some kind of marijuana charge.

In Utah, 59 percent of drug arrests in 1988, the latest year for which FBI statistics are available, were for marijuana use, compared with 27 percent for cocaine and other opiates.

Marijuana's popularity stems in part from the fact that it is a known quantity - almost 66 million Americans have tried it at least once, many of them during its heyday in the 1960s and 1970s. The 1988 National Household Survey on Drug Abuse found that 6.6 million Americans used it once a week or more and 11.6 million had used it in the previous month.

It is considered relatively safe. Today's marijuana may be far stronger than its counterpart a decade ago, as the government says, but Harvard psychiatrist Lester Grinspoon notes there is "no reliable evidence of death caused by cannabis in a human being."

And it's relatively cheap. John, a scientist who uses sinsemilla several evenings a week, says one ounce lasts him six months. That ounce could cost as little as $100 and the same amount of lower-grade marijuana can run $40.

Other drugs - especially cocaine and heroin - are associated with high crime and violence, particularly in the most populous states. Police officers last year arrested 700,000 people for cocaine and heroin nationwide, more than any other illegal drug.

But in some states, nearly every drug arrest involves marijuana - 86 percent in Vermont, for example, 82 percent in North Dakota and 81 percent in Maine, according to FBI figures for 1988.

Eight of every 10 marijuana busts is for possession of the drug, the FBI says.

The reason so many people are arrested on marijuana charges seems obvious to one group - the National Organization for the Reform of Marijuana Laws, which has advocated marijuana legalization for two decades.

Marijuana users "are easier targets" than, say, cocaine traffickers, said NORML spokesman John Dunlap. "They're a much more passive lot. The government knows it's an easy public relations victory."

Dunlap also contends there are just more marijuana smokers out there - he estimates 30 million people use it once a week, far more than the government estimate of 6.6 million.

Many police departments that once paid little attention to marijuana users have changed as attitudes harden toward all illegal drugs. An example is Arizona's Maricopa County, which includes Phoenix.

"The cops basically sort of ignored it" a few years ago, said Bill FitzGerald, spokesman for County Attorney Richard Romley.

Today, the county boasts a "Do Drugs, Do Time" program targeting all drug users.

"Every arrested person will be booked into jail for at least a few hours," said Romley and County Sheriff Thomas Agnos in a paper describing the program. For a casual user, even a brief jail stint "drives home the gravity of the offense."

First-time offenders may enter a diversion program and, according to FitzGerald's figures, three-quarters of the people who did had been arrested on marijuana charges.

Across America, government agencies have staged widely publicized raids on outdoor marijuana fields, indoor growing labs and stores that sell equipment for such labs in an attempt to curtail domestic crops that provide an estimated 25 percent of the U.S. supply.

Perhaps another reflection of changing attitudes about drugs, laws themselves are becoming more stringent.

Of the 11 states that decriminalized marijuana possession for personal use during the 1970s, four have reversed course in recent years.

Alaska, which had actually legalized possession of up to four ounces at home or other private places, voted Nov. 6 to make possession of small amounts a crime again.

Maine, Ohio and Oregon had already tightened marijuana restrictions. But in seven other states - California, Colorado, Minnesota, Mississippi, North Carolina, Nebraska and New York - a marijuana arrest is more akin to a traffic ticket than a criminal charge.

William J. Bennett, who resigned after 20 months as national drug control policy director, championed the stricter attitude and campaigned for Alaska's marijuana measure.

Although Bennett told The Associated Press last December that he believed marijuana was no more harmful than alcohol, he rejected legalization: "The last thing I would want to do is recommend the wider use of a drug that makes young people stupid."

Despite the increased risks, many longtime marijuana smokers cannot imagine giving it up.

John, the scientist who asked that his real name not be used, said a single puff of sinsemilla "facilitates the imagination and has allowed occasional creative breakthroughs," some of which have led to "papers published in reputable journals."