As mayor of the District of Columbia, Marion Barry has apparently developed a new branch of chemistry, which was the science he majored in at Le Moyne College. Call it political alchemy, the study of corrosive substances on government.

For example, under Barry's law, you can take a perfectly harmless substance like a minority set-aside contract, treat it with palm oil and, voila, a chemical change occurs that turns it into a kickback.

Or, take a visit to the home of a campaign worker. Add cognac and a federal wiretap and, whiff, it turns into a cocaine probe.

From his laboratory on the fifth floor of the District Building, the mayor continues to amaze his subjects with such concoctions. Just last Monday, he tried to cast a spell on the U.S. attorney's office, but that, too, blew up in his face.

Despite the mayor's failures, Barry is nobody's dummy. In fact, it was sheer wizardry that transformed this once-sleepy southern town into a veritable boomtown. Barry has always shown a knack for chemistry, especially equations that lead to explosions.

One day, you couldn't get a businessman to venture into downtown Washington to save his life. Then came an element known under Barry's law as the building block of all other substances: preferential treatment.

After experimenting for eight years with that special brew known as "home rule," Barry seemed to have found a way to make it work for residents. A structure was established whereas political power could translate into economic power for the people of this city.

But then the alchemy started going haywire. Scratch a minority set-aside businessman and it turned out to be a "rent-a-Negro," fronting for a white company that was still getting most of the money.

Shake the Department of Employment Services and you get one of the sharpest political minds in District government involved in a scheme to bilk taxpayers out of $190,000. Question a contractor and he will tell you how a handshake turned into a bribe.

Barry says be patient, that he is dealing with a complex and highly volatile formula that includes many unstable elements. Grace Shell, for example.

The mayor continues to maintain that his power is stronger than that of his adversaries, that as long as he can create a summer job for any youth that wants to work, as long as he can turn a drug-infested corner like 14th and U streets NW into a commercially viable block, he will reign supreme in the minds of voters.

Never mind that he has not learned how to make snow disappear, or Karen K. Johnson, for that matter.

Hours after filing a lawsuit to stop leaks about his relationship with Johnson, Barry ordered the withdrawal of a request for emergency court action in the suit. It seems that a key ingredient had been missing. Could it have been the truth?

Herbert O. Reid Sr., the mayor's legal magician, says, "If half of what I've heard is true, {any prosecutor} would go and get an indictment and put someone in jail."

But prosecutors practice patience, too, and have been known to take a decade before serving up their own concoctions. Anyway, the leaks continued. Johnson, according to sources, had told federal prosecutors that she received from $20,000 to $25,000 in cash in exchange for her refusal to testify before a federal grand jury investigating allegations of the drug use by the mayor.

But Johnson is a convicted cocaine dealer; the mayor has not been charged with anything nor convicted. Under Barry's law, the energy of a cocaine charge by a convict and the heat of a U.S. attorney's lightning bolt stir up the atmosphere to produce nothing more than gas.

And unless the mayor can come up with a rain dance or something to wash it away, voters may start casting a few spells of their own.