MOST RESIDENTS of the District are seriously concerned about violent crime and want courts to impose stiffer sentences on convicted felons. This is a natural reaction to a deplorable fact of urban life. It is easy to see why a recent poll taken by the Associated Press and WRC-TV indicated that 71 percent of the registered voters contacted favor Initiative 9, a proposal on the Sept. 14 primary ballot that would mandate minimum sentences for certain crimes. Its terms are summarized in an article by a supporter of the initiative on the opposite page today. It looks like a quick and easy way to tell the courts to get tough.

But it is not so simple. Without even making a judgment on whether such a law would deter criminals, as John Ray, a leading proponent, believes, it does not seem to be a feasible approach to crime in this jurisdiction.

There's an immediate practical consideration: Superior Court now has a backlog of 6,200 criminal cases, 2,200 of them felonies. To deal with these cases expeditiously and get the most dangerous felons off the streets, prosecutors plea bargain -- i.e., accept guilty pleas to some charges in order to avoid lengthy and costly trials. Eighty-five percent of all criminal cases are disposed of by accepting guilty pleas. But as former U.S. attorney Charles Ruff pointed out on these pages recently, very few accused will plead guilty if there is no room for compromise on the sentencing side. The result of requiring mandatory minimum terms, wrote Mr. Ruff, would be "chaos."

Then there is the question of first offenders sentenced to prison. Judges in this city already send more people to prison, in relation to population, than any judges in the country. Existing facilities are strained. According to Alvin Bronstein of the ACLU Foundation and Superior Court Judge Tim Murphy, adding 1,000 offenders to the prison system would cost $50 million for construction and $15 million a year to maintain the prisoners.

Finally, there are technical problems concerning the way in which the initiative is drafted. Already in the District a law requires mandatory mimimum sentences for first-degree murder and for second offenses with a firearm. The initiative would amend this law in a way that prosecutors fear would jeopardize the effectiveness of the existing law as it is applied to youthful offenders. Careful redrafting, in consultation with prosecutors, and public hearings are necessary before such a far-reaching change is adopted.

Opposition to this initiative does not indicate that the voter is soft on crime, only that he is hard- headed about the very practical problems it presents for the criminal justice system. For these reasons alone, the proposal should be rejected. Incidentally, the initiative is on a separate ballot from the primary candidates; you needn't be registered as a Democrat or Republican to vote on it.