The drive to decriminalize possession of small quantities of marijuana encountered its first "casualty" this year on the floor of the Michigan House of Representatives.

A female legislator became enraged by the statements of Ann Arbor's State Rep. Perry Bullard, who his made marijuana decriminalization a personal crusade, Calling Bullard a "pot smoker," she picked up an ashtray and gave her colleague a whack on the head.

Bullard wasn't seriously injured. Nor has political retribution been visited on legislator who've decided it makes no sense to burden offenders - mostly young people - with the stigma of prison sentences and criminal records for possessing small amounts of grass.

"No legislator in the state of Oregon has been defeated because of his vote for decriminalization. Not one, "Oregon State Sen. Ed Bagley told a National Conference of State Legislators panel in Detroit last month.

Nine states have eased up dramatically on their marijuana laws, generally making it a simple civil infraction if a person is caught with an ounce or less of the drug. Oregon was the first state to act, in 1973, Alaska, California, Maine, Colorado, Minnesota and just this year, Mississippi, New York and North Carolina have followed.

As a result, fully a third of the American people can now smoke the onetime symbol of decadence, evil and '60s radicalism without fear of anything more serious than a $100 fine, given out like a traffic citation.

The decrimination effort received a major boost recently when President Carter, making good on a campaign promise, asked Congress to reduce the federal penalty for possession of an ounce of marijuana from a $5,000 fine, a year in jail, or both, to a civil fine - probably $100. The President's stand should help persuade a still-reluctant Congress to change the federal law, says Keith Stroup, founder of the National Organization for the Reform of Marijuana Laws (NORML).

Even more important, Stroup says, the presidential stamp of approval should help persuade legislators to change state laws under which as astounding 416,000 marijuana arrests were made in 1975 - 93 per cent for possessing a small amount.

"People know that Jimmy Carter is not a social liberal," Stroup notes. "He's a compassionate man who has three sons who admit they have been marijuana users in the past - one of whom received a less-than-honorable discharge from the Navy as a result. His kids are not criminals, they're decent people. The fact that Jimmy Carter has come to grips with this on a personal basis makes it far easier for a lot of people to come to grips with it as well."

By 53 to 41 per cent, Americans favor removing criminal penalities for possessing small amounts of marijuana, the Gallup Poll says. What's causing the more lenient public attitude? There seem to be three major reasons:

Widely reported evidence that experimental or intermittent use of marijuana does not cause physical or psychological harm of dependency. Even with decriminalization, usage doesn't rise appreciably - only 3 per cent, Oregon and California studies indicate. No brain damage from marijuana use has been documented, unlike the well proven brain damage of alcohol.

A growing feeling that stiff laws alone will never stamp out marijuana use. "If we were to round up every kid in Sunflower County who smoked marijuana, we wouldn't have enough left to hold Sunday school," C.O. Sessums Jr., president of the Mississippi legislature. And the drug, notes Dr. Peter Bourne, Carter's assistant for health matters, can be cultivated in every state.

Increasing belief that jail and a permanent criminal record are more harmful to the marijuana user than the drug. There are stories of person rapes and even suicide among jailed marijuana users. "Our prisons are overcrowded, and yet were sending kids to jail for minor pot offenses. It just didn't make sense," says State Rep. Alan Adams, chief sponsor of North Carolina's decriminalization statute.

Decriminating marijuana, advocates say, frees up criminal justice money and staff to deal with more serious drug problems and serious crimes. California localities saved an estimated $25 million in court costs in six months following decriminalization - and also earned $800,000 in fines.

Drug control, Bourne says, should concentrate on life-endangering drugs. "People die from heroin, barbiturates, a minimal amount from cocaine, quite a bit from other hypnotic drugs and not at all from marijuana," he notes.

But he opposes full legalization of marijuana: "If you legalize it, it will be pushed, commercialized, condoned and people will encourage its use, which we don't want to do." It's undersirable, Bourne says, to have young people intoxicated with the drug for a significant percentage of the time, and there's an apparently of the time, and there's an apparently high correlation between marijuana and auto accidents.

Up to now, opposition to decriminalization has been strong in many states. Maryland, Missouri, Maine, New Jersey, New Hampshire and New Mexico all have turned down milder penalties since the decriminalization drive began. The issue's still pending this year in Michican and Wisconsin.

"We're not going to go out and lobby the states for decriminalization," Bourne told me. But the President's position, he hopes, will "set a tone with some kind of impact on leadership in state legislatures around the country."