Robert C. Randall, a studious, soft spoken 31-year-old ex-teacher with thick-lensed glasses, sits in his Capitol Hill apartment and lights up a marijuana cigarette, his sixth for the day.

He inhales briefly, then releases the smoke. There is no trace of emotion on his face.

The cigarette is a neatly rolled, fullsized, high potency, government-issued "joint." The marijuana inside is pea green in color and gives off an acrid odor.

Randall smokes marijuana -- 10 cigarettes a day, seven days a week -- in a unique U.S. government-sanctioned effort to help stem the spread of glaucoma, an acute eye disease that has damaged the optic nerves of both of Randall's eyes and left him partially blind. Without marijuana, his doctors say, he will probably go completely blind.

He is the nation's only legal smoker of marijuana as an antidote to glaucoma. Some cancer patients and research subjects are being given the active ingredients of marijuana on an experimental basis in pill form.

A former speech teacher at Prince George's Community College, Randall says he gets no "high" or other euphoric effect from the drug, despite or perhaps because of -- the enormous amount he smokes. "I've built up a complete tolerance to it," he says.

Since last May when he won an agreement in court from federal drug control authorities to use marijuana in conjunction with three other conventional drugs to combat the glaucoma, Randall has been receiving 70 high potency "joints" a week, prescribed by his private ophthalmologist and dispensed for free from a government pharmacy here in the city.

The present arrangement comes after a series of legal and bureaucratic battles waged by Randall and an array of lawyers, doctors and psychiatrists since 1975 to gain legal access to marijuana as medication.

He was enrolled in a research program in late 1976 but was dropped in January 1978 and went without legal access to marijuana until the government agreed to his present regimen last May after Randall filed a lawsuit claiming the government's refusal to give him marijuana denied his right to adequate health care.

"I can go to the neighborhood bar next door and buy any kind of cigarette for 65 cents and the surgeon general tells me on the pack it'll kill me," he said in a recent interview, "while it's taken three years of lawsuits and grinding tension to get permission to smoke marijuana to save my eyes."

Today, Randall says he devotes most of his time and energy to "stabilizing" his life and campaigning for expanded medical use of marijuana.

Behind him, he says, are the furtive days of growing marijuana plants on his back porch, getting arrested (and acquitted) and scouring the city for illicit supplies, ( $125 a week) to support "self-administration" of marijuana for his eyes.

Ex-teacher, ex-cab driver and sometime drama critic, the Florida-born Randall now lives in his comfortably crowded apartment on Capitol Hill with three cats, his books, his records, a shiny green cornhusk drosanthemum, wandering Jew and other hanging plants.

He supports himself with fees from periodic speaking appearances and is attempting to write a book on his experiences but says he is heavily in debt.

The marijuana he smokes is grown on a five-acre, federally controlled "pot farm" near Oxford, Miss., processed and rolled into cigarettes in North Carolina, shipped to Washington in brown-tinted plastic prescription bottles and dispensed to Randall by the National Institute on Drug Abuse.

Randall claims -- and many researchers attest -- that tetrahydrocannabinol, the major active ingredient of marijuana, helps relieve pressure on the eyeball caused by Glaucoma.

The pressure does not cause pain, Randall said, but creates "tricolored halos in my vision."

More important, he said, "the pressure is symptomatic of the disease, and if the pressure is allowed to remain high, there will be further erosion of vision."

A regular semiannual checkup by his opthalmologist last December showed "no progression" of the disease, Randall said. "That was a nice Christmas present," he said.

At the moment, he says, the central vision in his right eye is gone. "I can pick up color and shape only," he says. "It's like a bull's eye that somebody shot out."

His left eye still has some limited central vision, he said. "I can see.... It's like watching a 70 millimeter motion picture on a 9-inch Sony TV.... The detail is lost. There are 'gaps' or 'holes' in my vision."

In addition to marijuana. Randall takes three other more conventional pressure reducing drugs a long acting myotic called phospholine iodine, a "beta-blocking" substance called Timolol that also counteracts pupil contraction caused by the phospholine iodine and a pill form of diuretic to help draw off fluids from the eyeball area.

To obatin government consent to use marijuana, Randall's doctors had to certify that none of the conventional glaucoma drugs, alone or in combination, could relieve the pressure sufficiently to prevent blindness.

"I pay for the conventional medication," Randall said, "but the marijuana is free." (Medium grade marijuana is sold illegally on the streets of Washington for about $30 to $35 an ounce.)

Randall described the taste of his government-grown marijuana as "consistently bad... very metalic. It lacks the fine, almost perfumed taste of street marijuana."

The government-grown marijuana "is not made with much love or affection," he said. "People out at NIDA call it 'Bethesda gold.' It should be 'Bethesda green.'"

A former "light social user" of marijuana, Randall says he now gets no euphoric "high" from his medically prescribed drug. "It's a real kick in the butt," he said. "I view that as sad.... I found marijuana mellowing before."

When marijuana is taken as a medication, he said, "the whole recreational psyche is bled away... Also, I've built up a physiological tolerance because of the big dosages."

Randall smokes a total of 10 cigarettes a day, each containing a 2 percent level of tetrahydrocannabinol (TRC), about the twice the THC level found in ordinary street marijuana. He inhales lightly and does not hold the marijuana smoke in his lungs for extended periods, as social users often do.

Several researchers confirmed Randall's claim that he is no longer affected psychologically by the marijuana, especially in light of his heavy daily dosage -- 5 to 10 times that of the typical social user.

"I'm not surprised whatsoever that he's developed a tolerance to subjective effects at that level," said John Bachman, a psychologist at the Langley Porter Neuropsy chiatric Institute at the University of California in San Francisco where he has been conducting longterm research on marijuana tolerance with research colleague Reese Jones. "Our data confirms (Randall's) experience."

Randall says his daily regimen requires him to smoke marijuana in "clusters" -- two to three cigarettes in a row -- to ward off pressure peaks on his eyes that occur twice every 24 hours. He smokes the remainder of his 10 cigarettes per day at other intervals.

The dosage level of 10 two percent THC strength cigarettes per day was datermined by various doctors involved in Randall's case as the optimum amount needed to curb the spread of glaucoma in conjunction with Randall's conventional medication.

Several of Randall's doctors have also said surgery to stop the glaucoma is too risky and could lead to longterm adverse effects including total blindness.