KANSAS CITY, Mo. -- For centuries, people have smoked marijuana to get high and to get well. No doubt, pot dulls the senses. But scientific understanding of the weed's curative powers remains hazy.

Scientific studies produce hope and talk about pot's "potential'' but deliver little proof. A gush of anecdotal evidence is just that: stories that may, or may not, mean weed works wonders.

The foggy consensus about pot as prescription leaves doctors scratching their heads.

"Any doctor who deals with patients who are chronically ill and they tell you: `If I just smoke a joint, I can eat or feel better for a day,' it's hard to deny them that,'' said Kansas City physician Patrick Nemechek, who treats about 170 HIV-positive patients.

Meantime, the politics churn on.

Drug reformers talk about reefer as a miracle drug, a remedy of unrivaled versatility banned for its buzz. Anti-drug crusaders talk about a dangerous and worthless narcotic, its medicinal claims a cruel myth fashioned by legalization proponents.

Last week the president's drug czar warned California physicians that if they use a new state law to recommend marijuana, they could end up in jail. Two weeks ago, a prestigious medical journal editorialized on pot's behalf as a low-risk and promising drug.

Voters seem inclined to give doctors -- along with cancer patients, AIDS sufferers and glaucoma patients -- marijuana as an option. After all, who's going to deny a dying person a joint?

"For me,'' said a 34-year-old Kansas Citian with AIDS, "it means I can eat a meal and that my stomach isn't killing me. I don't see any harm in it.''

So far, 27 states lump marijuana with medically valuable drugs. The Missouri General Assembly passed a nonbinding resolution in 1994 asking Washington to make marijuana available for medical purposes. The Kansas Legislature hasn't tackled the debate. Lawmakers in six other states are considering the issue.

Federal law, however, makes those state designations mostly symbolic by outlawing possession, sale or use of the drug and by prohibiting doctors from prescribing marijuana. A handful of states -- most recently California and Arizona -- at least allow users to avoid criminal conviction if they can show they have a medical need.

The influential New England Journal of Medicine conceded only fuzzy evidence exists about the drug's therapeutic value while nonetheless endorsing its limited use.

"What really counts ... is whether a seriously ill patient feels relief,'' wrote physician Jerome Kassirer, "not whether a controlled trial `proves' its efficacy.''

But Columbia University psychiatrist Herbert Kleber, who is writing a response for a coming issue of the journal, counters that for nearly every medical application for smoking marijuana a more preferable and proven alternative is available.

"I would never say don't make it available as a medicine where we know it will really work,'' said Kleber, the medical director of the National Center on Addiction and Substance Abuse. "But we don't know where it works. Why put it out there if you're getting a significant risk and not a tremendous benefit?''

To be sure, the scientific assessment of pot's curative qualities is cloudy.

President Clinton's drug czar, Barry McCaffrey, in January ordered a $1 million review of "the state of knowledge of the health effects and potential medical use of smoked marijuana.'' It has been 15 years since the government last took a comprehensive look at the question.

"Cannabis and its derivatives,'' a blue ribbon panel concluded in 1982, "have shown promise in the treatment of ... glaucoma ... asthma (and in reducing) the nausea and vomiting of cancer chemotherapy. (But) marijuana has not been shown unequivocally superior to any existing therapy for any of these conditions.''

Research since shows some gains in squeezing compounds from the marijuana leaf to put its active ingredients into pill form. The drug Marinol, for instance, is popular for fighting off the nausea associated with the chemotherapy.

So the debate turns to whether smoking joints can do a body good:

In treating glaucoma -- considered one of the most promising applications of the drug -- the case remains unproven.

Glaucoma involves damage to the optic nerve, often from too much fluid pressure in the eye. It can blind people. Repeated studies demonstrate convincingly that marijuana protects vision by lowering that fluid pressure.

Yet the Glaucoma Research Foundation "does not advocate the use of marijuana (because) there are no conclusive studies to date that indicate marijuana (or its components) safely and effectively lowers intraocular pressure enough to prevent optic nerve damage.''

The group also calls marijuana a poor alternative because glaucoma is a chronic disease that requires ongoing, long-term treatment. Pot also may damage vision by decreasing blood circulation to the optic nerve.

Oddly enough, sucking marijuana smoke into the lungs provides short-term relief for asthma by opening bronchial tubes wider.

But long-term, chronic pot smoking does just the opposite, causing those bronchial tubes to constrict and aggravating asthma.

For AIDS sufferers, pot has a growing following for the way it stimulates appetite -- recreational users call it "the munchies'' and subsequently fights the condition's wasting syndrome.

The issue, however, is whether smoking reefer is better or worse for the appetite than swallowing Marinol pills. Smoking pot actually gives patients better control over their dosage. Yet even marijuana advocates concede there's not enough research to answer the question.

The nausea and vomiting that accompany chemotherapy -- a common, effective and miserable treatment for many cancers -- dissipates for some people who smoke marijuana.

Studies have shown that the body absorbs more of marijuana's key ingredient, tetrahydrocannabinol, from smoke than from pills. Yet the American Cancer Society sees it as a last resort. Other anti-nausea drugs "have been shown to be more useful.''

"It's not particularly effective across the board, but it may be effective for some people some times,'' said LaMar McGinnis, medical consultant to the American Cancer Society. "It should be available as a controlled substance.''

Still, the studies fall short of clear answers. One reason: It's tough to test pot.

With so many other drugs, researchers can develop placebos (often a sugar pill) to give to one group of subjects and the real thing to another. Neither group knows who got the real thing. That, in turn, guards such "double blind'' studies against any benefits that are only imagined.

Yet with marijuana there's nothing with the same taste, smell and buzz that comes from smoking a joint. So when chemotherapy patients say marijuana makes them feel less nauseated, it's difficult to conclude whether their stomachs are settled or whether being high clouds their physical symptoms.

What's more, pot's recreational reputation scares away grant money for studies. And private drug companies are reluctant to spend research dollars on a natural substance that will carry no patent royalties.

For all its prohibitions, marijuana remains popular. Physician David Butcher of the Kansas City Free Health Clinic said that about a quarter of his HIV-positive patients use marijuana, although only 5 percent to 10 percent use it for medicinal purposes.

"Some of these people don't need to be adding more foreign substances to their lungs,'' he said. "But they also tell me that it works for them. We need more studies on it.''

Users speak of it almost religiously, a salvation from dry heaves and disappearing pounds.

"If I don't have a joint first thing in the morning with my other medicines,'' said a 41-year-old Kansas Citian with AIDS, "I'm a mess.''

He and most of his friends smoked pot for fun before AIDS came along. And, he admits, sometimes the line separating his medicinal and recreational use of the drug is blurred.

"Sure, it's nice to just cool out with a joint and enjoy it,'' he said.

As for its legal standing, the drug remains plentiful and comparatively affordable. A month's supply of the drug Marinol can cost $500. Users say a quarter- to a half-ounce of pot will last a month and cost $50 to $100.

"I'd rather not worry about the cops and all,'' said one man, "but it's not like I can't get it.''

(The Kansas City Star web site is at http://www.kcstar.com )