At the heart of much American law enforcement and criminal justice is the word that few are willing to utter out loud: discretion.

Justice is blind and the law is the law, but in the courts and on the streets, the thing we call justice reeks of discretion, depends for its functioning on decision making by cops and judges and prosecutors, operating in a world quite removed from the “letter of the law.”

Barely was the ink dry on the Massachusetts law and subsequent ballot question decriminalizing small amounts of marijuana when many police departments mumbled that they weren’t inclined to enforce the thing, which empowered them to issue $100 citations for possession. Are the cops free-thinking libertarians? No, the problem is, the law reeks of discretion, which means the first time the cops cite too many minorities, or not enough minorities, or some wealthy valedictorian from a snobby suburb, for holding a little weed, it will be the cops who are indicted by the law of public opinion. It’s all about discretion.

South Carolina is mulling the appeal of a gambling conviction by five cheerful poker players who, legal issues aside, want the state to grow up. State law in South Carolina says any game of chance, with cards or dice, is illegal, even if you’re playing in your living room with your buddies. The real issue here? Discretion. A prosecutor this month in Idaho suggested that the legislature loosen up the goofy state laws against gambling, because no one seemed inclined to enforce a ban on home poker games. What was he really saying to state government? Exercise some discretion, because the cops already do.

Early this month in Connecticut, the cops conducted one of those giant, invading-Iraq kind of gambling raids on a cock fight in Waterbury, where about 50 roosters and 24 humans were taken into custody. Although every state has finally (and in some cases, grudgingly) made cockfighting illegal, the Northeast tends to be more inclined to unleash the armies of truth and justice against the cranky roosters than are, say, New Mexico or Louisiana. It’s all about discretion.

Who’s Who

When tired urban downtowns pretty up the landscape a bit by going after the creepy fellows hanging around Main Street, the legal system has a discretionary nervous breakdown, as cops and courts pretend there is some precision to the definitions of “trespassing” and “loitering” and “panhandling” and “aggressive begging” and, of course, every cop’s discretionary fallback, “disorderly conduct.”

The American Civil Liberties Union and the city of Portland, Ore. have been wrestling in court over a list of chronic offenders who seem to be targeted by local cops when they stray downtown, lowering real estate values and annoying the tourists. Perhaps, the cops are not exercising sufficient discretion. Or, perhaps, too much discretion.

Nowhere is discretion wielded with more enthusiasm than in the nation’s juvenile courts, where the young criminals, their parents, and often the “victims” as well, are such basket-case creatures that the prosecutors, defense attorneys and judges do a little social-worker dance that has little to do with the ‘law” — and much to do with sorting out the various pathologies.

Much of the murkiness associated with law enforcement is understandable; legislation, regulation and ordinance are often designed to be more symbolic than real. In the case of the Massachusetts’ marijuana decriminalization, the law is intended to signal cops to lay off the low-level drug busts, rather than to actually lay out a precise standard for what constitutes a crime and what constitutes a mere irritation.

How will the local cops know that the ounce of marijuana is, in fact, marijuana? Is it worth a lab test and subsequent report to justify a $100 fine? Will these hardened criminals actually pay the fine? If not, will local cops go after them with a vengeance, because the law is the law?

No, much like the speed limits on the Mass. Pike, the idea is to lay out some vague guidelines that suggest you can cheat a little bit, but you can’t drive 90 mph; and you can smoke a joint, but you can’t bring garbage bags full of marijuana to a Pats game. Discretion runs both ways.