HARRISBURG, PA. -- A hard-charging federal prosecutor targets personal drug use among top government officials. Defense lawyers cry foul, contending the U.S. attorney's office is conducting a political "witch hunt."

That may sound reminiscent of the debate over D.C. Mayor Marion Barry's trial on drug and perjury charges. It is happening instead here, as a federal grand jury steps up its probe into cocaine use among a network of white-collar professionals that allegedly reached high into Pennsylvania and federal law enforcement and included a longtime aide to Attorney General Dick Thornburgh, a former governor of Pennsylvania.

A series of court hearings and motions in recent weeks has stunned residents of this state capital, revealing allegations of repeated cocaine use at parties, golf outings, restaurants and local nightclubs by prominent lawyers, businessmen, stockbrokers, and present and former public officials. Among the key targets of the probe, court records here show, are Richard L. Guida, the former director of criminal investigations in the Pennsylvania attorney general's office, and Henry G. Barr, who between September 1988 and May 1989 held one of the most sensitive jobs in federal law enforcement as Thornburgh's special assistant charged with overseeing and helping to coordinate criminal investigations across the country, including drug cases.

But while Barr's alleged involvement has given the case prominence, and prompted Thornburgh to recuse himself, the investigation also has stirred debate over what some say may be its larger policy implications. Rarely, if ever, has the Justice Department mounted such an exhaustive inquiry into what are essentially charges of drug use that do not also involve dealing or trafficking, according to some defense lawyers who have argued their clients were the victim of "selective prosecution."

Under the direction of Assistant U.S. Attorney Gordon Zubrod, as many as 50 witnesses have testified before the grand jury and in many cases were pressured -- under the threat of perjury charges -- to identify longtime associates, friends and others with whom they used cocaine, no matter how long ago or how small the use.

Failure to prosecute officials for drug use "breeds the conclusion . . . that there are two sets of rules; one if you are a private citizen, if you are black or Hispanic," but another for law enforcement officials under which "you can do the same thing and get away with it," Zubrod said during a recent hearing on a plea agreement in the case.

Informed at one point that he had flunked a FBI polygraph test about his cocaine partners, Guida then supplied the names of two former girlfriends. In another instance, FBI agents reportedly grilled a witness about the use of cocaine during a Trivial Pursuit game five years ago.

"This is overkill . . . it's a witch hunt," charged William C. Costopoulis, a well-known local defense lawyer. "We're not talking about killers or rapists here. We're not even talking about drug dealers. We're looking at people who got high and now we're going to burn them. I don't see anybody coming out of this looking good, including the government."

But Zubrod, an ex-Marine who has gained a statewide reputation for aggressive prosecution of drug-trafficking cases, has nonetheless presented the investigation in court as a "case of national significance" -- a test of the government's willingness to prosecute drug use among white middle-class professionals, including public officials, at a time when the brunt of federal law enforcement has fallen on blacks and other minorities.

The investigation began nearly two years ago as a routine drug case when agents raided the home of a suspected local cocaine dealer and found an ounce of cocaine, an unregistered Uzi and a small phone book filled with the names of local businessmen, with a series of bookkeeping entries written next to them.

Through interviews with the businessmen, the agents eventually compiled testimony against Guida, a flamboyant local defense lawyer who resigned from the Pennsylvania attorney general's office in September 1986 amid allegations by a radio reporter that he was a "cocaine addict." Guida had flatly denied charges of drug use in the past. But this time, presented with the new evidence against him, he agreed to plead guilty to one count of cocaine possession and identify others with whom he used cocaine -- including Barr.

The scope of the testimony first emerged earlier this month when Guida's lawyer, former federal prosecutor Paul Killion, filed a motion indicating that at least five witnesses -- including Guida, one of Guida's law partners and a local investment banker -- have told the grand jury they used cocaine with Barr, delivered cocaine to him or saw him use it on repeated occasions starting at a New Year's Eve party in 1984 and continuing until sometime in either late 1987 or early 1988.

When they first heard the allegations about Barr, "all of our reactions were the same -- amazed, stunned, shocked," said Murray G. Dickman, Thornburgh's top assistant for personnel matters who worked with Barr in Harrisburg and shared a house with him and two other Thornburgh aides in Alexandria. "I would describe Henry as a straight-arrow person. . . . He was more of a law enforcement person than anybody else down here."

Law enforcement sources said federal investigators have recently received additional allegations that Barr continued to use cocaine after September 1988, the date when he began work in a fifth-floor Justice Department office just down the hall from Thornburgh. That prompted FBI agents to recently interview five of Thornburgh's top aides -- all of whom said they had no knowledge of Barr's alleged drug activities.

Barr, who quit the Justice Department May 12 of last year, citing personal reasons, did not respond to numerous messages on his answering machine. "I have no comment about anything," said Charles Scarlata, Barr's lawyer, when contacted on Friday.

Meanwhile, Zubrod continues his pursuit and two weeks ago persuaded a federal district judge to vacate Guida's plea agreement after charging that the lawyer had flunked an FBI polygraph by denying his use of cocaine with another "high-ranking" state or local official who was not identified.