Law enforcement authorities here are instituting a major get-tough policy that will prohibit drug offenders in the District of Columbia from pleading guilty to lesser charges if they do not agree to cooperate with police or become informants.

One of the main purposes of the new approach is to put more pressure on drug users and lower-level peddlers to provide information that could lead to stronger cases against persons up the ladder in the drug hierarchy, law enforcement officials said.

The new plan was begun by U.S. Attorney Charles F. C. Ruff after an internal study of his office's drug prosecution policies showed that nearly 60 percent of the persons indicted on fellony drug charges here last year were allowed to plead guilty to less serious, misdemeanor charges.

Federal sources said most of those plea arrangements were almost automatic, with prosecutors offering the lesser pleas merely to clear cases off court dockets.. Seldom were any defendants in those more routine cases asked to cooperate with police.

Ruff, concerned about the apparently routine and one-sided lowering of charges by prosecutors in drug cases, has assigned seven highly experienced trial assistants to develop and monitor the new project.

Last year, felony indictments were filed in the D.C. Superior Court system against 246 drug defendants.

These were the cases viewed as the most serious, and they did not include the hundreds of marijuana arrests made by police each year.

However, 149 of those defendants ultimately were allowed to plead guilty to lesser charges involving the same drug cases. According to incomplete sentencing statistics, only one-third or less of those who pleaded guilty received any jail sentences.

The focus of the new drug project will be an attempt to force suspects arrested with even small amounts of heroin and other hard narcotics to inform authorities about their suppliers, according to prosecutors setting up the special narcotics unit, which will review daily every drug arrest.

Only if a suspect cooperates with police will he or she be allowed to enter into plea negotiations, prosecutors said.

In the past, the major concerted effort against drug offenders here focused on prolonged investigations of narcotics conspiracies and international drug trafficking organizations. The more routine arrests by police officers tended to "fall between the cracks," according to criminal justice system observers.

Prosecutors assigned to the D.C. Superior Court system have routinely paid little attention to drug cases, according to internal studies by the U.S. Attorney's office.

Those prosecutors also handle murder, rape and robbery cases and, in that context, "prosecutors may not put the same significance on a narcotics case," said Assistant U.S. Attorney E. Lawrence Barcella Jr., who will head the new unit.

"We're going to be working much harder to develop narcotics intelligence by exerting appropriate leverage on individual defendants," Barcella added.

Ruff's top aide, principal assistant U.S. Attorney Robert W. Ogren, aknowledged that the abrupt shift in plea bargaining policy will place a heavy burden on addicts and others who have been treated more leniently in the past.

But, he added, the prosecutors have decided that "the only way to go after the big offenders is to treat the smaller offenders harshly."

Prosecutions of drug offenders in Washington are complicated by overlapping, confusing and sometimes contradictory criminal statutes that can be applied in drug cases.

Various attempts to streamline the city's narcotics laws have failed, usually because politicians have tried to tack controversial marijuana decriminalization amendments to the measures.

The new narcotics unit's top priorities are heroin and certain pills used by addicts to boost the "high" caused by heroin, and will not change the law enforcement community's relatively lenient treatment of marijuana users here.

One of the thrusts of the new unit will be to apply the available statutes differently in order to shift many cases involving small quantities of drugs out of federal court. There, judges privately complain about the insignificance of such minor charges and seldom impose jail terms. In D.C. Superior Court, the judges see a wider array of drug charges and are more likely to impose sentences.

The primary function of the new unit, which will include at least two full-time investigators from the D.C. police department and the U.S. Drug Enforcement Administration, will be to consolidate the narcotics function of the U.S. Attorney's office, Barcella said.

In the past, a narcotics charge brought into the criminal justice system here could be handled by any one of six different divisions of the U.S. Attorney's office, Barcella noted. Now all of them will be directly handled by the new unit or at least reviewed by the new unit the same day they are filed.

By bringing more cases in the Superior Court system rather than in federal court prosecutors also will be more likely to keep drug offenders in jail immediately after their arrests.

"There is more flexibility in bail laws in Superior Court," Barcella said. For example, under federal bail statutes it is extremely difficult for prosecutors to argue successfully that someone should be held in jail for more than a few hours after an arrest.

In Superior Court, however, prosecutors may ask routinely that persons who are on probation or parole be held for five days without bond, or may invoke the preventive detention statute -- something that has never been done in a drug case. Neither option, which could pressure defendants into talking, is available in federal court.

Although the new unit is being set up to deal with narcotics cases, it also will handle non-narcotics cases involving persons believed to be major drug traffickers here, Barcella added.

The new unit is patterned after another special unit set up in the U.S. Attorney's office here four years ago to deal with repeat offenders charged with violent crimes. That unit has a conviction rate of more than 90 percent, an unusually high percentage in criminal cases.

"We want to make the price for trafficking in drugs more than most people want to pay," said assistant U.S. Attorney William O'Malley, also assigned to the unit.